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2020.07.01 04:27

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Coronavirus Pandemic

By JoAnne Castagna, Ed.D.

The Novel Coronavirus (COVID-19) surprised us all, especially our nation’s hospital system which was not prepared for a pandemic. Hospitals throughout the United States, especially in New York State, are overwhelmed with patients with Coronavirus symptoms and can’t provide them beds.

“We’re inundated” said Tara Clampett, Intensive Care Unit, Registered Nurse with Long Island Community Hospital. “A majority of them are going into respiratory distress and are being intubated. Even if they get stable, many aren’t stable enough to leave.”

She says that with many Coronavirus patients coming to the hospital, this leaves less space for patients with other health conditions, so less attention will be given to their health issues.

The hospital did all it could do to create more patient space, but it is not enough.

To relieve the burden of New York State hospitals, the U.S. Army Corps of Engineers, New York District, is collaborating with other agencies to convert existing buildings into alternate care facilities to provide hospitals extra space to care for Coronavirus and non- Coronavirus patients.

“What the Army Corps is doing is making me hopeful. We are overwhelmed and we can use all the help we can get,” said Clampett.

The U.S. Army Corps of Engineers is performing this work as part of a national Federal Emergency Management Agency (FEMA) mission. The Army Corps is working in collaboration with FEMA, Department of Defense, and other federal, state and local partners.

In New York State, this work is considered especially critical. The state, primarily New York City, is considered the epicenter in the Nation. There are more virus cases and deaths in the state than anywhere else in the Nation.  At the time of this article’s publishing there were 222,284 cases and 14,636 deaths.

To accommodate all of these cases, it is estimated that the state may need more than 100,000 hospital beds for Coronavirus patients, compared to the state’s current capacity of 53,000 beds.

To help New York State hospitals deal with this, Army Corps’ New York District volunteers are working 24 hours a day, seven days a week.  They are locating existing buildings that can be converted into these alternate care facilities and then they are designing and constructing them.

Four key locations have been identified and they include the Jacob K. Javits Convention Center in New York City, Westchester County Center in White Plains, New York, Stony Brook University in Stony Brook, New York and the State University of New York in Old Westbury, New York.

Jacob K. Javits Convention Center, New York City

The first alternate care facility to be constructed – and completed in one week – was the Jacob K. Javits Convention Center, located in midtown New York City. The center is a well-known location for expos and business events.

The center’s great size of 1,800,000-square-feet, seemed like a good location for an alternate care facility.

The Army Corps converted the center’s multiple floors of space into an alternate care facility, providing beds for more than 2,500 Coronavirus and non-Coronavirus patients.

The facility was designed and constructed to resemble a hospital setting. There are rows of individual patient care units or rooms that include beds, privacy curtains, medical supplies and equipment. In addition, there is overhead lighting, restrooms, showers, nursing stations, food service and an computer station, powered by multiple generators.

While touring the center, Chief of Engineers Lt. Gen. Todd T. Semonite said that in order to quickly and efficiently get these centers up and running for a peak in Coronavirus cases, a “super simple solution” had to be applied.

He said the Javits Center’s design will serve as the model for other care facilities being constructed throughout the nation.

Charles Paray, Lead Architect, New York District, U.S. Army Corps of Engineers said, “I volunteered to work on Jacob Javits and the other alternate care locations because I thought I could help make a difference.”

Westchester County Convention Center, White Plains, New York

The center is known for its large gatherings for basketball tournaments and live shows.

The Army Corps is converting 60,0000 square-feet of the center into an alternate care facility, providing 110 beds for Coronavirus patients.

Fifty-four of these beds will be located inside the center and fifty-six will be located in a temporary tent structure located in the center’s parking lot across from the center.

Both areas will be designed and constructed to resemble a hospital setting. There will be rows of individual patient care units or rooms that will include beds, privacy walls, medical supplies and equipment, and the rooms will be equipped to provide oxygen/medical gas for patients.

In addition, there will be overhead lighting, restrooms, showers, nursing stations, food service, and an computer station, powered by multiple generators.

The facility will also be equipped with an isolation exhaust fan with HEPA filtration located outside of the facility, so that contaminated exhaust air within the facility is discharged to outside the facility.

“I’m working on the Westchester Center because I want to help to provide additional hospital space for nurses and doctors to take care of our neighbors who have been diagnosed with the Coronavirus,” said Patrick Nejand, Quality Assurance Representative, New York District, U.S. Army Corps of Engineers.

Stony Brook University, Stony Brook, New York

The Army Corps is converting 255,676-square-feet of the university’s campus to provide care for 1,028 non-Coronavirus patients and low acuity Coronavirus patients.

They are building five climate-controlled tents on an open field on the campus grounds.

Inside these tents it will resemble a hospital setting. There will be rows of individual patient care units or rooms that will include beds, privacy walls, medical supplies and equipment.

In addition, there will be overhead lighting, restrooms, showers, nursing stations, food service, and an computer station, powered by multiple generators.

“New York is the epicenter of the COVID-19 Pandemic in the nation and that is why we worked diligently and swiftly to complete four alternate care facilities in New York,” said Col. Thomas Asbery, Commander, New York District.

“I am honored and humbled to lead this team of experts and professionals who have set the standard for the emergency response to this public health crisis. What we did in New York is historic and unprecedented and will be carried out many times over Nationwide. Nonetheless, we still have much more work to do as we support FEMA, New York State and our local partners and stakeholders across New York. The U.S. Army Corps of Engineers will continue to work tirelessly at all levels in helping the American people recover from the effects of the COVID-19 Pandemic.”

Anthony Ciorra, Mission Manager, New York District, U.S. Army Corps of Engineers, who is working on the Stony Brook Alternate Care Center said, “My brother contracted the Coronavirus in March and become very sick. He developed pneumonia and was admitted to a hospital for 10 days.”

He said, “This is an unprecedented time in all our lives and I wanted do my small part in making a difference in a monumental effort to fight this virus.”

State University of New York at Old Westbury, New York

At the university, the Army Corps will provide beds for 1,024 Coronavirus and non-Coronavirus patients.

They are building four climate-controlled tents in a large expanse of athletic fields and another unit in a gymnasium.

Inside these tents it will resemble a hospital setting. There will be rows of individual patient care units or rooms that will include beds, privacy walls, medical supplies, and equipment.

In addition, there will be overhead lighting, restrooms, showers, nursing stations, food service, an computer station, powered by multiple generators, and overhead cameras to enable medical staff to monitor patients.

“William Maher, Mission Manager, New York District, U.S. Army Corps of Engineers, who is working on the State University of New York at Old Westbury Alternate Care Center said, “We’re meeting the challenge of building a high-quality patient care facility in a very short period of time.”

Army Corps personnel are used to volunteering for national missions. Nejand volunteered for recovery operations for Hurricane Sandy and 9-11.  He said, “During missions, I’m always impressed with the Army Corps ability to quickly mobilize personnel with local knowledge with technical experts nationwide to provide comprehensive response with methods to maintain accountability of all costs and scheduled completions.”

These volunteers give more than just their time for these missions. “A lot of people are putting not only their lives, but the lives of their love ones at risk to get this mission executed,” said Paray.

Presently, some of these alternate care facilities are completed and are assisting hospitals throughout New York State, lessoning some of the burden on their medical staff.

Not only are hospitals grateful for the Army Corp’s work, so are the Coronavirus patients.

Kevin McGann, who was hospitalized with Coronavirus symptoms said, “Based on all of the numbers coming out of New York State’s Governor Cuomo’s daily briefings, I support the Army Corps mission 100-percent.”

The 49-year-old New York City resident added, “Use tents, convert dormitories and hotels, and do whatever needs to be done to prepare for the possible onslaught of patients. Worst case is we look back and realize we didn’t need all of them, but better to have them than have to decide who lives and who dies.”


Dr. JoAnne Castagna is a Public Affairs Specialist and Writer for the U.S. Army Corps of Engineers, New York District.  She can be reached at Joanne.castagna@usace.army.mil.

The post U.S. Army Corps of Engineers comes to the aid of hospitals appeared first on Civil + Structural Engineer magazine.


Three Lessons from a Virginia Town’s Decade of Success

By Deborah K. Flippo and Shawn Utt

The promise of brownfields redevelopment is that once-blighted property seen as a liability can be reimagined and repurposed into a community asset that spurs additional investment and serves as a transformational catalyst. For the many communities around the country that still grapple with how to address brownfields and potentially contaminated sites, this vision can seem more like a dream than anything else. Although navigating the road to success can be complex and challenging, the experiences of certain communities stand as a testament to the true potential that brownfields redevelopment can bring.

Nestled in the rolling hills and mountains of Southwest Virginia, the Town of Pulaski has become a surprising and seminal example of brownfields redevelopment. Surprising because a town in the heart of Appalachia has defied the odds and seminal because Pulaski’s example has inspired other communities to structure similar brownfields redevelopment strategies.

Before. Photo: Draper Aden Associates

Since the town’s brownfields program was launched in 2009, Pulaski has seen over $10,000,000 of economic development capital investments by several private companies, tourism developments, and community improvements. These private investments were spurred by the town’s brownfields program and have helped transform Pulaski from a heavy manufacturing and industrial based economy to a vibrant commercial and service economy.

In over a decade, Pulaski’s team of citizens, leaders, local officials, and consultants have learned a number of important lessons. Three key factors to the success of a brownfields redevelopment program include planning, community buy-in, and ongoing program administration.

Significant and Strategic Planning

Planning is a crucial step for any community that wants to launch a brownfields redevelopment program and secure financial support from the Environmental Protection Agency (EPA) in the form of grants. Early planning is critical and should begin by identifying potential sites that could qualify as brownfields. The number of sites in a community is a factor as is the potential to redevelop those sites.

Applying for EPA Brownfields Grants is a time intensive process and increasingly competitive, but worth the effort. These three-year grants were the foundation upon which Pulaski’s program was built. Towns and cities should partner with an established and experienced consultant to help them evaluate brownfields sites and complete the grant application process.

A final planning component is to create partnerships of support in the community. These partnerships can be among community members, business leaders, and others. This broad-based support is a factor in EPA grant evaluation and is necessary to make brownfields redevelopment a reality on the ground.

It’s important to note, though, that coalitions also can be built across jurisdictional boundaries. Multiple municipalities can consider a broader partnership to help secure EPA grant funding. A great example is the regional partnership formed by the City of Williamsburg, James City County, York County, and the Greater Williamsburg Partnership in Southeastern Virginia. This coalition secured a $600,000 Community-Wide Brownfields Coalition Assessment Grant from the EPA in 2019.

EPA grants often get a lot of attention, but don’t discount available funds from state entities. Pulaski has benefited significantly from state-level support in Virginia, for example. The Virginia Brownfields Assistance Fund, funded by the Virginia General Assembly and administered jointly by the Department of Environmental Quality and the Virginia Economic Development Partnership, awards grants that can be used for brownfields planning and remediation. This support can be crucial for brownfields redevelopment.

Community Support

As highlighted in the planning section, community support is fundamental to the success of a brownfields program. In Pulaski, the town’s Economic Development Board — composed of leaders from throughout the community, and representing businesses, community organizations, local government, and health care – evolved from a community oversight group to an energized brownfields redevelopment steering committee. Their efforts and enthusiasm sparked the beginning of Pulaski’s renaissance.

Collaborating with community leaders and economic development officials to support brownfields redevelopment will be helpful in the EPA grant process and will remain vital throughout the program as sites are identified and redevelopment is encouraged.

That ongoing support can make larger brownfields redevelopment more attainable as well. In Pulaski, the most alluring brownfields project was also the largest to date: the Jackson Park Inn and Conference Center. A former three-story building constructed in the early 1920s that lies adjacent to Town Hall and across the street from Jackson Park, the building had various owners and sat vacant for years. The site was identified during a brownfields assessment and targeted for redevelopment. The result is a $5,000,000 investment by a local developer that transformed the building into a boutique hotel and conference center that also includes a bar and restaurant with outdoor seating on Peak Creek.

Program Administration

Once a community has committed to a brownfields redevelopment program and funding has been secured, the next phase begins. Ongoing program administration is an absolute requirement from the EPA. This administration will ensure that sites are properly identified and help incentivize brownfields redevelopment.

Identifying the right team members, internally and externally, can make all the difference in proper program administration.

How you leverage initial grant money will play a major factor in any potential future rewards. Those communities that can show progress and success are well positioned for additional three-year grants. Pulaski’s ongoing revitalization is credited in large part to the continued success in securing brownfields grants. The town has now secured four awards for the highly competitive federal brownfields funding, which along with state brownfields assistance funds, totals over $1,500,000. These funds have facilitated Phase I and Phase II environmental site assessments as well as remediation and redevelopment planning for about 25 sites to date. These results aren’t possible without proper program administration.

The story of Pulaski is one of hope, revitalization, and a promising future. The town’s robust brownfields redevelopment program has been a catalyst to transform this community. Projects have included major investments, an international business locating its U.S. operations in the town, and a renovated minor league baseball stadium helping enliven downtown. Pulaski also has seen projects specifically focused on its citizens. For example, a brownfields site located adjacent to Peak Creek received state Planning and Remediation Grants to facilitate assessments, conceptual planning, demolition, and soils remediation. The current plan is to redevelop the site as a public recreation complex with a skate park and basketball facility connected to downtown via a promenade.

Brownfields redevelopment can bring an enhanced economy and quality to life to communities that once thought they were mired in blighted, unproductive and potentially contaminated brownfield sites. The future can be bright, and lessons from Pulaski’s brownfields redevelopment success provide a roadmap to making that future a reality.


Deborah Flippo is Economic Development Program Manager with Draper Aden Associates, a Mid-Atlantic engineering, environmental services, and surveying firm. Based in the firm’s Blacksburg, VA office, she leads efforts on economic development, including brownfields redevelopment. She has worked with regional organizations, cities and towns in Virginia and North Carolina on brownfields redevelopment grants and programs. Deborah can be contacted at dflippo@daa.com.                                                                                      

Shawn Utt has served as Pulaski’s Town Manager for the past seven years and served as the County’s Director of Economic Development for seven years prior. He is keenly aware of the power of “cleaning the slate” using the Brownfields Grant program funding which has helped to keep the Town of Pulaski’s rejuvenation moving forward. Shawn can be contacted at sutt@pulaskitown.org. 

The post Transforming Communities Through Brownfields Redevelopment appeared first on Civil + Structural Engineer magazine.


By Brian M. Fraley

Nothing good can come of a severe thunderstorm unless you happen to be on the receiving end of an emergency contract to clean up the aftermath. Cushnie Construction Company, Inc. encountered this situation on the island of Kauai in Hawaii starting on March 16, 2020.

“We had a hell of a flood on the island with 20 inches of rain,” says the company’s Vice President Ralph Cushnie, noting that he believes this storm was a record breaker.“ A bunch of debris came down the river and we basically had a log jam of debris at the Wailua Bridge.”

Cushnie, founded 12 years ago, is a family-owned Women’s Business Enterprise run by Ralph’s wife Laura. The sitework contractor works strictly on the island of Kauai, serving private and public sector clients including local, state, and federal government.

Clearing the Log Jam at a Compromised Bridge

The main problem was heavy erosion damage to the concrete reinforced wall near the north abutment of the bridge, and scouring that was causing instability around several piers, according to Hawaii Department of Transportation (HDOT). Cushnie was already clearing nearby flood-damaged areas, and owns a unique clamshell attachment so HDOT decided to award the contractor the emergency contract.

The first challenge was a 120-foot uprooted tree that was swept downstream and came to rest against the side of the bridge. Cushnie’s crews worked around the clock for a week to get it removed.

More debris soon followed, but fortunately the raging river never rose high enough for the debris to breach or pass over the bridge. “Another big rain like this could have knocked that whole bridge over,” Cushnie says.

Clearing debris from the bridge was job one. Overhead wires prevented the use of a long-reach excavator. Cushnie set up two excavators on the one-lane bridge deck. The machine with the clamshell scooped out the debris and piled it on the deck where a five-man crew downsized it to manageable sections with power tools. Another nearby excavator with a grapple loaded the material into waiting trucks.

The next step was to get the debris to the processing sites. Desirable laydown areas were at a premium because of the flood so Cushnie dumped half in a stadium parking lot, and the remainder at two other locations. The problem that remained was how to process the material efficiently.

Searching for the Right Attachment

“We had started grinding the logs and they were too big for our shredder to deal with,” Cushnie recalls. “We were just looking on the internet for something and we came across Ransome Attachments and the Black Splitter Cone Splitter,” he says. The problem was that he didn’t want to lose time on the extra processes associated with hydraulic attachments, including switching hoses and unpinning buckets.

The alternative was to mount a hammer on the excavator to split the wood, but damaging the pavement in the stadium would have been unacceptable. Cushnie learned of the Ransome Shark Tooth RST 150 Stump Splitter/Harvester. It had the functionality, but its single serrated edge is designed for sawing and digging out rooted stumps.

The Ransome Shark Tooth Stump Splitter/Harvester was mounted on a mid-size excavator to size down logs and stumps for processing by the Crambo 6000 Dual-Shaft Shredder.

Adding Teeth to the Shark Tooth

The Shark Tooth has a serrated edge on the outside blade with a flat edge and thumb on the opposite side, which works well for its primary purpose – splitting, removing, and loading stumps. Cushnie’s operation called for more teeth because the crew would have to quarter wood on flat surfaces where the timber is not anchored.

“We had nothing to anchor to,” he says, noting that they were cutting on pavement at the stadium and dirt in the other locations. “We were going to put the tooth in and then work it back and forth.”

The clock was ticking. Ransome quickly agreed to modify the attachment by adding a second serrated edge, creating an attachment that looked like a spade with jagged edges.

“The reason we wanted the front edge serrated is because we were basically just pinning the wood to the ground and then wedging the point into it,” Cushnie explains. “When you uncurl the arm of the excavator, you’re getting that cutting action on the front edge, while going back and forth and wedging and splitting at the same time.”

Feeding the Crambo Shredder

The role of the Ransome Shark Tooth Stump Splitter/Harvester was to size down material for feeding into the Crambo 6000 Dual-Shaft Shredder. The shape of the logs was a factor as well.

Dropping a log without a flat edge into the Crambo Shredder would be like running on a log in the water, according to Cushnie.” If you put one of those six-foot logs in the hopper it would roll around for an hour in your shredder,” he says. “If you halve or quarter it, it’s got that straight edge so the Crambo can bite into it and start shredding.”

The majority of the wood came from albizia, a tree that has been deemed an invasive species in Hawaii. The wood was a bit softer and stringier, but splitting it was still challenging because the trees were still green since they had just been uprooted.

The Shark Tooth delivered adequate power, despite being mounted on a mid size Komatsu excavator. “It was all green so it took some effort,” Cushnie says. “Once it dries out, you just tap it and it splits.”

Much of the smaller debris was loaded into the Crambo with a standard bucket. The Shark Tooth was required for splitting stumps and logs over six feet. Chainsaws were used to get the largest pieces down to that size.

Most competing attachments that Cushnie looked at required thumbs to be unpinned, which would have reduced productivity. The Shark Tooth’s can attach to a quick coupler and works in conjunction with an existing thumb. This allowed Cushnie to split and load the Crambo in one continuous process.

The debris was ultimately processed into mulch and given to a local coffee farm and landscaper. No one can accurately predict whether Kauai will see a storm of this magnitude but one thing is sure: Cushnie will be prepared with the right equipment.

About Ransome Attachments

Ransome Attachments of Lumberton, N.J., supplies durable, cost-effective, multi-functional attachments to the forestry, landscaping, recycling, municipal, demolition, and general construction markets. Its diverse mix of attachments – including wood splitters, screening buckets, grapples, concrete pulverizers, post drivers – fit both compact and heavy equipment. Visit ransomeattach.com to make a connection.

The post Modified Ransome Shark Tooth Splitter Helps Contractor Save Hawaiian Bridge appeared first on Civil + Structural Engineer magazine.


It was the bridge nobody wanted. At least, that was how it felt to Tad Molas and Adrian Moon when 150 opponents packed the house at the first public meeting to discuss replacement plans for Daytona Beach’s Veterans Memorial Bridge.

“The Daytona Beach community was very attached to their bascule bridge, and there was a strong public desire for the replacement bridge to be of similar design, so as not to change the character of the area,” said Moon, who served as the construction project manager for WSP USA on the project. “The plan was to replace it with a high-level bridge, and there were fears that it would forever alter the landscape of the area compared with a low-profile bascule bridge.”

“A high-level bridge was also seen as tougher for the pedestrians and cyclists who used the bascule bridge regularly to cross the canal that separates two parts of the Daytona Beach community,” added Molas, design project manager for WSP. “This was not going to be an easy process … but something worthwhile isn’t always easy. In the end, this bridge benefitted from those early challenges.”

Amazingly, a process that began in 2015 with a large crowd of sign-carrying protesters ended with applause, cheers and praise from the same community that is now welcoming its new Veterans Memorial Bridge with open arms.

WSP designed the replacement of the bridge along Orange Avenue, which spans Daytona Beach’s Intracoastal Waterway. The new bridge follows nearly the same alignment as the existing bridge, which minimized environmental and right-of-way impacts.

The $38 million bridge, which is scheduled to open to traffic in July, is the culmination of a concentrated effort to involve the public directly into the design process to create a greater sense of ownership in the project, while still meeting the budget and the needs of the clients, Volusia County and the Florida Department of Transportation (FDOT).

Save Our Bridge

The 1,885-foot-long bridge features a vertical clearance of 65 feet and a horizontal clearance of 125 feet – dimensions required by FDOT and the Coast Guard to accommodate the boats that use the Intracoastal Waterway.

It was this height, and the anticipated steep grade that would be necessary for the relatively short bridge to clear the channel, that generated the most public opposition. Sure, motorists and pedestrians experienced delays when the drawbridge was activated to accommodate water traffic, but many felt the low profile of the bascule bridge and the unobstructed coastal views were worth this occasional inconvenience.

Before they stepped into the first meeting with the community, Molas and Moon knew they had their work cut out for them. But they also had a plan to turn opponents into advocates.

“The first thing I set out to do at that meeting was to find the champion of the opposition, talk to her and more importantly, listen to her,” Moon said. “We even went out together to take a look at the original bridge, and by the end of the conversation she was sketching ideas she had for the bridge. Hopefully she left that evening realizing that there was no enemy, and that these guys were here to help.”

To help incorporate the community as a partner in design, the county established a Project Advisory Committee (PAC) that included a select but diverse combination of local residents, veterans, business and community leaders and elected officials. Meetings were held a dozen times over the next nine months and were used by Moon and Molos as opportunities to explain technical concepts, receive input and propose solutions for the committee’s approval. This blended concept development and outreach process was critical in building advocacy and creating excitement for the project.

“It didn’t happen overnight, but at each meeting, we would show genuine regard for what the public had to say about the design,” Molas said. “They had a lot of really good ideas and provided a valuable local perspective that deserved our attention.”

Designers introduced refinements to the plan at each meeting, incorporating what had been discussed at the previous meeting. Even when it was a relatively modest but important suggestion – such as the installation of charging stations to accommodate the elderly population who use battery-powered scooters to cross the bridge – it was given serious attention and became an integral part of the plan.

PAC members not only helped the study team better understand community concerns and priorities, but also served as a critical link back to their constituents, sharing the progress of the study and receiving valuable feedback from the public. Ultimately, their endorsement of the bridge design was what turned public enthusiasm in favor of the project.

“The public gradually took ownership of the overall design,” Molas said. “They helped establish the vision, and the engineers and designers worked with the client to find ways to make it work.”

That idea of ownership extended further than either Moon or Molas anticipated, as the committee started viewing the project from the client’s perspective, sometimes suggesting that certain aspects of the project might be unnecessary or too expensive.

Historic Design – Modern Construction Techniques

Much of the community saw the old bascule bridge as an important part of their personal history. It was always there; always a part of their life. It couldn’t just be replaced with a standard bridge. And to properly honor Volusia County veterans, it should be something special.

“As it was going to be a bridge to honor America’s military veterans, we gathered input from veterans on the committee throughout the design process, and they were favoring an arch bridge design that was common in the 1920s and 1930s that looked powerful and formidable – which they saw as a symbol of the strength and perseverance of military veterans,” Moon said.

Incorporating a non-traditional design ran the risk of significantly increasing the cost of the project. Arch bridges of this type typically used extensive and costly cast-in-place (CIP) construction. So the complex bridge design team, led by WSP’s project engineer-of-records Victor Ryzhikov, P.E; and Christopher Vanek, P.E., developed an innovative concept to maximize the use of pre-cast components, including all arch and superstructure components, “A CIP approach was simply not practical today, so we came up with an evolutionary design that precast those segments in the controlled environment of a casting yard, and then brought them to be assembled at the site, sort of like Lego blocks,” Molas said.

The bridge is composed of a pure concrete open spandrel arch bridge with a main span through-deck arch over the waterway. During construction, the beams and main span arches were hoisted into position by cranes, then closure pours were used to connect all the elements together. 

It was these connection points, and the order of their assembly, that Ryzhikov and Vanek focused much of their design efforts towards. The connections must be small, compact, but incredibly rigid and reasonably easy to assemble on site. Although the open spandrel approach spans were constructed only with closure pours, the longer main span through arch required a combination of longitudinal and transverse post-tensioning to create a rigid frame, that could be supported via PT hanger bars over the channel.

As part of the design process, 3D BIM was utilized to verify constructability and accuracy of the complex connection points. The 3D drawings also aided in plans review and were ultimately used by the CEI and contractor for reference during construction.

Pedestrian Friendly Design

The design also achieved another PAC objective – lowering the overall profile of the bridge.

“The arch was a simple way to carry the weight of the bridge from above rather than below, creating a thinner profile over the channel while still meeting the minimum height requirement,” Molas said. “The arch allowed us to create a much shallower deck than conventional designs would, lowering the roadway profile at midspan significantly compared to the nearby segmental bridge that has the same navigational requirements. Though it may not seem like much, it did lower the grade for pedestrians and lowered the overall profile of the bridge. The through-arch design solved a lot of engineering problems for us.”

There were some concerns that the contractor may perceive the unusual precast design approach as risky. So using the same BIM models developed during the bridge design, WSP developed set of 3D design and bridge visualization sheets that clearly showed contractors how to assemble the precast elements. Contractor feedback indicated that the 3D approach to plan production reduced the “contingencies” that contractors carried in their bids.

Another way 3D visualization came in handy was with the use of a 3D printer to create a stunning model of the bridge design.

“It was one of the best ways to help everyone visualize the bridge before construction began and had an impact far beyond all of our expectations,” Molas said. “There was a visually impaired man that attended every meeting, as well as one on the project advisory committee itself, and when we set up the 3D printed model at one of the meetings, he was able to use his hands to help visualize and understand the shape of the structure. That was an amazing moment. Several visually impaired residents were able to experience what the bridge might look like thanks to the 3D model.”

A Community Bridge

The bridge design took into account the needs of the region’s senior citizens, and resulted in a bridge that exceeds the requirements of the American’s with Disabilities Act, featuring a lower grade, wider sidewalks, a walkway that connects the north and south sides with an underpass to avoid crossing in traffic, charge stations for scooters and educational signs in braille.

The completed bridge also includes a series of overlooks for pedestrians and cyclists, offering fantastic views of the coastal city and featuring plaques that tell the story of each of America’s wars as well as recognizing the contributions of military veterans who fought in those conflicts.

“It has really made this bridge a destination for the local community,” Moon said. “There is an educational circuit that begins on the southeast side and ends on the northwest side, where plans are in place to create Veterans Memorial Park.”

The Memorial park plans were also designed by WSP, and although tethered to the bridge project, will be funded and built separately through the support of the county, private donors and veterans’ groups.

Veterans Memorial Bridge is the biggest public works project in the history of Volusia County, and that was a responsibility that Moon and Molas both took extremely seriously.

“As a design team we wanted to lay it all out there, leave no stone unturned,” Moon said. “We recognized that this was an opportunity that does not come along very often. We committed to it from day one to make it the most it can be, took that approach to everything, and expected the same commitment from everyone involved in the design and construction of the bridge.”

Josh Wagner, Volusia County council member and PAC chair, said the community was fortunate to have WSP working on the bridge.

“It is clear that WSP’s goal has been to go above and beyond in every aspect of our community project,” Wagner said. “They have been very sensitive of the costs for the project. As with any project, costs are a major concern. We have benefitted from WSP’s extra efforts to find cost reductions.”

“The great thing we discovered is that anyone can do something like this,” Moon added. “It didn’t require extraordinary funding; but rather a choice made by the owner to do something special, and a commitment to find the best, most efficient ways to make a vision a reality. And equally as important, a philosophical willingness to involve the community in the process as much as possible.”

The post Veterans memorial bridge: Reimagining the Conventional Arch Bridge appeared first on Civil + Structural Engineer magazine.


By David Wallace, P.E.

Along the south side of downtown Fort Worth, Texas sits Interstate 30, Tower 55 Rail Intersection—one of the nation’s busiest railroad intersections –and a newly revitalized urban, mixed-use neighborhood and medical district called the Near Southside. Originally, Interstate 30 ran elevated over a major east-west corridor on the south end of downtown but in the early 2000s, the highway was relocated further south to a more industrial area which include a highly active east-west railroad corridor. When the new highway was built, it flew over the railroad tracks leaving an underpass to be excavated in the future to connect a perpendicular street, Lamar (on the north) and Hemphill (on the south). Since then, the long-held desire of the City of Fort Worth to connect the central business district to the south side of town via an underpass tunnel that provides a safe, multi-modal route to and from downtown, gained momentum.

Construction of the four-lane vehicular, pedestrian, and bicycle tunnel – known as the Hemphill Street Connector – was awarded to McCarthy Building Companies’ Southern Region under a Construction Manager at Risk (CMAR) contract – a delivery method not often seen within the transportation sector. Under the CMAR delivery model, the benefits to an owner begin in the design phase. The construction manager’s early involvement improves the design through its insights on constructability, value engineering, cost estimating, and schedule. Additionally, unlike other delivery methods, CMAR provides the owner with a skilled advocate throughout the project which also procures the subcontractors who then perform the work.

Construction Management

While long planned, moving the project forward was extremely challenging as there were more than eleven stakeholders to coordinate including TxDOT, Union Pacific Railroad, Downtown Fort Worth, Inc., Near Southside Inc., I-CARE, and multiple others. Further, the project underwent several iterations of design and bidding, and multiple delays during the procurement phase. Under the CMAR contract, McCarthy worked with the City of Fort Worth to align the large group of stakeholders and seek consensus to what was best for the community. McCarthy also assessed all project risks and worked to proactively plan these risks out of the project. The general contractor coordinated self-perform and the subcontractors’ work to achieve the highest daily productivity. The team addressed construction coordination among various subcontractors, evaluated their manpower levels, and ensured they performed their work in accordance to the overall construction schedule. McCarthy also managed the Stormwater Pollution Plan, environmental plans and practices as well as tracked the flow of major materials from initial submittals through fabrication and delivery to coincide with the proper construction sequence.

Construction sequence on the project was vital as it was a multi-phased and complex job with various scopes of work that included a railroad track shift to maintain functionality and other special track work, structural steel bridge construction, deep foundation drilled shafts, waterproofing, earthwork and rock excavation, temporary shoring, rock nail and shotcrete retaining walls, precast panel retaining walls, CIP retaining walls, living “greenwall” retaining walls, storm drainage, concrete pavement, tunnel lighting, street lighting, traffic signals, landscaping and irrigation, metal handrails, signage and pavement markings, and public artwork.

Building Connection

The multi-phased project began with constructing a new rail bridge to support four existing Union Pacific Railroad lines that run through the Tower 55 Rail Intersection at the east limit of the project. With more than 100 trains passing through each day, this is one of the nation’s busiest and most congested rail intersections. To construct the railroad bridge, McCarthy shifted four existing railroad tracks north in a shoofly configuration for each of the separate tracks. The bridge was built in four phases – two adjacent to live rail traffic and two in the middle of active tracks. The bridge beams and deck came in large sections of married pairs or triples with the diaphragms already installed and the deck plates welded on. These sections were very heavy, which, when coupled with minimal space for access, required two crane picks for most segments. For the first phase of bridge, the beams were picked from Interstate 30 which required nighttime lane closures. Remaining phases had to be completed above active traffic.  Additionally, the soil in the railroad right of way was bid as 100 percent TCEQ Class 1 waste. McCarthy was able to segregate, stockpile, and test the soil as it was excavated, and determined that a large portion of it was not contaminated. This resulted in a credit back to the City of Fort Worth of over $1.2M. This action and savings are benefits of working with a CMAR contractor. A hard-bid contractor would have hauled it all off as contaminated, costing substantially more for removal because they would want to get paid the higher unit cost. However, CMAR has a 50 percent shared savings so McCarthy worked hard to mitigate additional costs.

Next, crews focused on excavating under the highway and constructing a four-lane roadway and two 10-foot pedestrian pathways underneath Interstate Highway 30. When excavating the area under the Interstate and railroad tracks, the team encountered extremely hard limestone rock approximately seven feet below grade. Because of that, the excavation effort essentially became a pure mining operation with low overhead clearance and the knowledge that Fort Worth’s main freeway had thousands of cars passing over the excavation site daily. Further, storm sewer lines had to be installed nearly 40-feet deep through this hard rock. This required a large excavator and hydraulic hammer to trench through the rock. The deep trenches require engineered shoring systems and planning for safe access and fall protection.

Finally, it was time to construct the underpass section. Because the crews were working under active auto and train bridges, there were significant shoring measures required, including rock anchors and shotcrete to prevent cave ins. Building the retaining walls and roadway alignment was especially difficult due to the complex horizontal and vertical curvature of the roadway as it descended under the bridges and snaked its way to connect the two intersections. There was no flat plane to be found, and each segment of the walls had to conform to the curves, which was constantly checked by the full-time survey crew on site. Working under the bridges to install the precast wall panels required diligent planning and careful operations to be able to set the panels and place the closure concrete with limited overhead space. The precast walls tied into the existing drilled shafts for support, which had to be exposed and have dowels installed. The drilled shafts for the new bridge were placed with a steel embedded plate at the face. Once the shafts were exposed, nelson studs were welded to the plate to anchor the retaining walls to the shafts. Lastly, the center piers for the new railroad bridge were poured full height, with sonotube formwork to produce a pleasing finish to the columns once excavated and exposed.    

Positive Impact

Infrastructure projects are not typically labeled as “Quality of Life” enhancers, but the new Hemphill Connector – with its vehicular, pedestrian and bicycle tunnel that improves traffic flow and promotes community cohesion – truly moves the neighborhood to a better place. Be it the living green walls, safely lit over-sized pedestrian and cyclist paths, or the public art piece entitled “Flight” by nationally renowned artist Dan Corson, this underpass enriches life and fosters relationships. More and more public entities are choosing infrastructure projects that benefit process and people, in this case, eliminating human barriers and connecting individuals, to the benefit of a refreshed and vibrant community.

During the project, McCarthy worked closely with non-profit organizations that promote the ongoing redevelopment of the Near Southside as a vibrant neighborhood with affordable housing options and safe streets to walk on. The organizations see the district as a destination, rather than just pass through on the way to a different part of town, and they believe that the Hemphill Street Connector will be a strong catalyst for the district’s continued redevelopment by increasing interest from new investors, businesses, and residents.

CMAR for Transportation

From enhancing design through effective constructability reviews, to creative scheduling and overall project management, CMAR benefits civil and transportation projects on many fronts as it facilitates higher quality with on-time delivery at a lower cost. Partnering with McCarthy under a CMAR contract worked well for the City of Fort Worth and the Hemphill Street Connector project because of the Teams Risk Mitigation Strategies:

  • coordinating multiple stakeholders
  • mitigating unknown and/or unforeseen conditions
  • deftly maneuvering through this highly phased project
  • leading the franchise utility relocations; both public and private developments adjacent to the work
  • supporting public relations and communications, which were paramount; and
  • finally, McCarthy created allowances and contingencies and led as a partner and advocate to contend with the project conditions.

The Hemphill Street Connector project was successful in showcasing the benefits of the CMAR delivery method – thru which McCarthy ultimately completed the project five months early and saved the city nearly $4M.


David Wallace, P.E is a senior project manager for McCarthy Building Companies, Southern Region. He can be reached at DRWallace@mccarthy.com.

The post Tunneling to Connect Fort Worth appeared first on Civil + Structural Engineer magazine.


About 40 miles west of Washington, DC along the I-66 corridor, Prince William County, Virginia has been experiencing rapid growth. In Haymarket, VDOT implemented Northern Virginia’s first Diverging-Diamond Interchange (DDI) to alleviate congestion and accommodate future growth in the area.

The project included the construction of two parallel bridges for RT 15 to cross I-66. Both bridges used Reinforced Earth® MSE walls at the pile-supported abutments, for a total of four walls. The square concrete facing panels were cast with a dry-stack stone architectural finish, then painted in the field to match the cast-in-place traffic barrier on the bridge deck.

The design-build team included Rinker Design Associates as the lead designer, with Lane Construction as the general contractor.

The southwest MSE wall abutment shown, with precast concrete facing to match the bridge parapet.

The DDI was chosen for its innovative method of improving capacity and safety. The design moves traffic over the bridge to the opposite side of the road. The traffic light system reduces wait time, and the crossing pattern eliminates left turns into oncoming traffic. According to VDOT, the system has twice the capacity of a traditional diamond interchange.

In 2018, the project won the DBIA Design Build Project of the Year as well as the VTCA Transportation Engineering Award for design-build.

The post Reinforced Earth Walls Support Northern Virginia’s First Diverging-Diamond Interchange appeared first on Civil + Structural Engineer magazine.


| Tervlap
2020.07.01 11:38

Kép

A lebegő szállodáknak nincs szükségük kiépített kikötőre. Szép sorban sorakoznak egymás mellett a parthoz közel. A hetvenkét méter hosszú, tizenhat méter széles, négy emelet magas épületek mindegyikében 101 szoba szolgálja a vendégek kényelmét, de egy étterem és egy lounge bár is helyet kap a komplexumban, mely összesen 1616 kiadó szobát...

| AEC Magazine
2020.07.01 10:03

Image Integration of cloud-based collaborative tools to help teams stay connected during Covid-19 lockdowns

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| AEC Magazine
2020.07.01 09:49

Image ‘Location intelligence’ said to enable collaborative and connected on-site experiences and streamline construction workflows

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| STRUCTURE magazine
2020.07.01 09:40

Incorporating Resiliency to Coastal Designs in The Florida Panhandle

Hurricane Michael, a Category 5 hurricane, made landfall along the Florida Panhandle on October 10, 2018, with a direct hit between Tyndall Air Force Base and the coastal City of Mexico Beach, leaving a trail of destruction in its path. The damage extended over sixty miles east and west of the eyewall. The areas affected the most experienced sustained winds of 161 miles per hour (mph), a minimum pressure of 919 millibars (mb), and a storm surge reaching 19 feet above sea level with additional wave action well over this elevation. Hurricane Michael was “directly responsible for 16 deaths and about $25 billion in damage in the United States,” according to a report prepared on May 17, 2019, by the National Hurricane Center.

I think most people, including myself, were shocked. How could Mother Nature do so much damage in three hours? We had no idea at the time that the winds were over 160 mph and storm surge was over 17 feet. Seventy years gone in just three hours.
~Mexico Beach Mayor Al Cathey

Aerial photograph of Mexico Beach as rebuilding is underway.

Aerial photograph of Mexico Beach as rebuilding is underway.

Upon further investigation of the variation of wind and flood damage in coastal areas like Mexico Beach, Port St. Joe, Cape San Blas, and Bay County, the overwhelming majority of homes built to the current 6th Edition of the Florida Building Code (based off the 2015 IBC), and within the guidelines set forth by the FEMA regulations within the 100-year floodplain and ASCE 7-10, survived the storm with minor to moderate damage. Among the variety of observed failure modes, the most common within structures built utilizing the current Florida Building Code were shear wall failures (ranging from inadequate sheathing thickness to an insufficient number of fasteners), complete lack of shear walls, excessive scouring, and impact from flood and windborne debris. The overall load paths and uplift connections performed very well, confirming that the minimum design parameters and installation methods required by the current Florida Building Code are satisfactory for structural integrity and overall public safety if the design wind event is met. FEMA’s Technical Bulletin 9 establishes a standard for construction of break-away (frangible) structures built below the base flood elevation within the 100-year flood plain. Following Hurricane Michael, it was evident that most structures built in the last 10-15 years, to the specifications recommended in FEMA Technical Bulletin 9, performed as intended during the devastating flood event. In most cases, the ground floor walls designed to be frangible were torn away from the piling supported structures as the storm surge rose and wave action increased. This allowed for the reduction in surface area in which the hydrostatic pressure and velocity driven impact were able to act, reducing the overall lateral load experienced by the pilings supporting the superstructure above.

It was obvious when you walked the streets that the newer building code was successful. Unfortunately, the majority of the houses were older style houses that created a domino effect when the storm surge came, causing extra damage to newer buildings.
~Mayor Cathey

Following Hurricane Michael, local municipalities reacted with resiliency in mind to prepare future structures and developments to withstand the extreme effects of similar storm events. For example, the City of Mexico Beach has amended the pre-Hurricane Michael flood ordinance, which required structures to be elevated above the FEMA 100-year flood plain. The pre-existing flood ordinance required the lowest horizontal structural member (LHSM) to be elevated to a minimum of 1 foot above the FEMA designated 100-year flood elevation within the (VE) flood zone (coastal high hazard area subject to water including wave action). Furthermore, within the VE flood zone designation, all solid walls below the minimum LHSM elevation were required to be break-away (frangible) and were not to exceed 299 square feet of enclosed space. All structures within the AE flood zone designation (stillwater flood elevations and wave effects less than three feet) were required to have the finished floor elevation (FFE) elevated to a minimum of 1 foot above the FEMA designated 100-year flood elevation. There was no limit on the square footage of enclosed space below the FFE elevation within the AE flood zone, and the only requirement was to install flood vents to equalize hydrostatic pressure in the event of a non-velocity flood event. Following Hurricane Michael, the City voted to raise the freeboard to 1.5 feet above the worst-case flood elevation. Within the new ordinance, this is considered to be the maximum of the following: FEMA VE (100-year), FEMA AE (100-year), and FEMA X (500-year).

Performance-based design utilizing a moment frame to maximize openings on a new coastal home in Port St. Joe (Gulf County).

Performance-based design utilizing a moment frame to maximize openings on a new coastal home in Port St. Joe (Gulf County).

We adopted an eighteen-inch freeboard over the 500-year floodplain. It was hard to ignore what just happened. The Council felt comfortable adding this freeboard to the 500-year floodplain because the only maps we have are the “best available” by FEMA, and these flood elevations are still a work-in-progress. We do not know what the final flood zones will be. I think Mexico Beach did the right thing to try to give property owners the best protection that we could.
~Mayor Cathey

In many cases, the 500-year “X” flood zone designation governs the required FFE and LHSM elevations, requiring some structures to be elevated up to 5-6 feet above the previous flood ordinance requirements. In addition to the new flood ordinance, the City of Mexico Beach increased the minimum design ultimate wind speed to 140 mph as opposed to the 130-mph requirement that was in place before Hurricane Michael. This wind speed requirement is compatible with Gulf County, just to the East of Mexico Beach. Although residents were extremely vocal in their concerns with the changes to the flood ordinance due to the associated increase in construction costs, they were very receptive to the idea of amending the minimum ultimate design wind speed to 140 mph. Additionally, all structures considered to be substantially damaged, as described within FEMA substantial damage guidelines, are required to be either demolished and reconstructed to meet the current codes or undergo improvements to bring the entire structure up to current codes.

What we have in Mexico Beach is remarkable, unlike any other community. Citizens, business owners, frequent tourists, and citizens of surrounding communities showed great resiliency to rebuild the pieces of what was lost and protect what we still have.
~Mayor Cathey

In many cases, performance-based design is implemented in coastal communities and other areas prone to natural disasters like hurricanes. This methodology considers a design approach that will protect the functionality and maintain the intended service and use of structures to continue to meet the needs of the owners and users. In the wake of a natural disaster, the term resiliency becomes a key factor in rebuilding a community. Most property owners that endured the devastation associated with Hurricane Michael want to ensure that, as they rebuild their homes, businesses, and more, all sensible measures are taken to ensure that their investment can withstand a similar storm event. Performance-based design presents the ability to meet the aesthetic and functional demands of homeowners and developers for the intended use of the structure while remaining within the established budget. The designer has the comfort level of providing a conservative design to suit the wants and needs of the Owner, while also preparing for the unknown, whether it be defective building materials, human construction errors, or natural disasters. This is especially important in Hurricane prone regions that are subject to high wind-speeds and velocity storm surge because the damage is unpredictable and highly variable. This approach can be suitably utilized with other climatic hazards as well.

Many of the homeowners and commercial developers have witnessed, firsthand, the destruction that Hurricane Michael left in its path. It is very common to have an Owner ask questions related to the structural stability and overall resiliency of specific building materials as they plan to rebuild. Some simply want to know what siding is best, and some want to know whether to use cast-in-place concrete construction, insulated concrete forms (ICF), or conventional wood-framed construction. Others ask if their proposed structure can be designed to a 180-mph wind-speed. As stated above, the implementation of the existing Florida Building Code, in conjunction with performance-based design, provides a resilient design approach that will produce structures that perform to their intended durability and overall expected life and performance.

The primary concerns with the rebuilding efforts in the areas affected by Hurricane Michael are the availability of contractors, skilled workers, and sub-contractors. It is not uncommon, nearly eighteen months after Hurricane Michael made landfall, for local Builders and General Contractors to have an eighteen- to twenty-four-month backlog before they can begin a new project. Local Planning and Building departments, as well as the Florida Department of Environmental Protection (FDEP) and other coastal permitting agencies, have adjusted in a commendable manner to facilitate the influx in new construction. Within the entire coastal area impacted by Hurricane Michael, residents, as well as municipal and governmental entities, have united to make the best of the situation presented. Each week, more and more homes are being completed, as businesses are also beginning to re-open their doors to provide much-needed services to this community.

Conclusion

Due to the on-going determination and perseverance of the residents and local government agencies within these coastal communities, the Florida panhandle is on its way to rebuilding with the same resiliency that the people of this area have shown time and time again since October 10, 2018.■


| STRUCTURE magazine
2020.07.01 09:30

In the fall of 2016, a project team began to investigate the deterioration, causes, and possible treatments to stabilize and repair the limestone cladding panels of the former May Company department store (renamed the Saban Building). The building was gradually being renovated to form part of the new Academy Museum of Motion Pictures.

The façade rehabilitation team came late to the project. Previous façade engineers recommended complete demolition and reconstruction of the historic façade utilizing new corrosion-resistant supports and 100 percent waterproofing. But the Academy Museum wished for restoration compliant with the requirements of the Environmental Impact Statement and other planning restrictions relating to the Los Angeles Cultural Historical Monument’s protected status. The Museum saw the conservation approach as aligned with its sustainability and preservation objectives; the old building, after all, was the largest object in the Museum’s newly developing collection. In turn, the City’s Office of Historic Resources also deemed a conservative approach to the cladding to be most appropriate, since it would preserve original materials as well as the historic character and design of the A. C. Martin masterpiece.

Original detail of the historic limestone panels and steel window boxes show embedded steel angles and kerf dowels into the limestone panels.

Original detail of the historic limestone panels and steel window boxes show embedded steel angles and kerf dowels into the limestone panels.

Work included reviews of previous reports; visual inspection of the limestone panels, interspersed with protruding steel window shadow boxes and frames; field pull-out testing of helical friction anchors; exploratory openings to observe concealed conditions; corrosion potential assessments; the design of an amended ASTM E488 engineering laboratory test to account for the performance of headless friction anchors; a trial mockup swing-stage installation of replacement panels and Dutchmen; negotiations with Los Angeles Department of Building and Safety; the production of full construction documentation; and, construction administration support services.

Limestone panel edges located along corroded steel shelf angles were spalling and cracking.

Limestone panel edges located along corroded steel shelf angles were spalling and cracking.

Existing Façade Condition

The historic Saban Building’s exterior walls consist of steel beams and columns encased in reinforced concrete, infilled with reinforced concrete walls. The façade consists of 3-inch-thick limestone panels, approximately 4 feet wide by 5 feet tall, each weighing up to 900 pounds, with 1 inch of grout backing and joints with Type N and S mortar. Limestone panels consist of vein-cut panels and cross-cut panels across all exterior elevations, vertically supported on unpainted mild-steel shelf angles that are welded to embedded steel plates in the concrete wall. As the limestone panels sit on the shelf angles, kerf anchors extend from the horizontal leg of the angle and sit in a kerf slot in the limestone panels. Mild-steel dowels provide side-to-side panel connections.

Test rig assembly shows shear loading on the helical anchor installed through the limestone panel. Courtesy of Specialized Testing Inc.

Test rig assembly shows shear loading on the helical anchor installed through the limestone panel. Courtesy of Specialized Testing Inc.

Moisture intrusion through open and cracked mortar panel joints caused corrosion of the steel shelf angles and kerf dowels. Water intrusion was exacerbated by the heavy stone panels sitting on top of the window boxes, depressing their thin steel box ‘tails’ and causing the top of the windows to drain into the wall. This condition was made worse by some of the kerfs not welded to the steel box heads (as designed) but instead wire-tied through holes in the metalwork, thus affording more water ingress to the otherwise unprotected support structure. The volumetric expansion of the steel, from the corrosion spalled portions of the panel edges, caused cracks along some panel tops and bottoms. Thus, the out-of-plane restraint of the limestone panels was compromised. Vertical support at heavily corroded shelf angles posed falling hazard conditions along the exterior of the building.

Table of statistical analysis of Helifix anchor testing results.

Table of statistical analysis of Helifix anchor testing results.

Table of design capacities of Helifix anchors.

Table of design capacities of Helifix anchors.

Façade Retrofit

Helical friction anchors were proposed to secure the limestone panels to the exterior concrete walls and replace parts of damaged panels in-situ. However, helical anchors have never before been used in this application in the City of Los Angeles. The true capacity of the anchors and the connection assembly were determined through material testing, following the requirements of ASTM E488 Standard Test Methods for Strength of Anchors in Concrete Elements. Additionally, since the material properties of limestone panels used in such applications were not available, additional hydraulic dilation and temperature tests were performed on limestone samples to determine the behavior of the stone when exposed to water or excessive heat.

Countersunk anchors blend in with natural voids on the stone surface.

Countersunk anchors blend in with natural voids on the stone surface.

The testing procedure mimicked the installation of helical anchors into existing configurations of the limestone panels with grout backing on the concrete wall. Tapping tests of the existing panels determined unbonded grout backing in some cases. Thus, a worst-case scenario was used for the testing, assuming that the grout was unbonded and/or cracked and made no contribution to the cladding stability. In place of grout backing for the test, Teflon slip membranes were placed at the interface between the limestone and the concrete panel so that the true tensile and shear capacity of the helical anchors without the grout backing was tested. Matching Cordova Shelly Limestone panels were obtained from the same Texas quarry system as the original limestone panels and used throughout the testing to mimic the extant façade behavior closely. Pre-test assessments took place to determine which drift (bed orientation) of cross-cut or vein-cut stone would perform the weakest and whether dry or wet saturated stone affected test results; the worst case was adopted for full testing.

Anchors tested to shear failure showed localized crushing in the limestone in shear. Courtesy of Specialized Testing Inc.

Anchors tested to shear failure showed localized crushing in the limestone in shear. Courtesy of Specialized Testing Inc.

ASTM E488 is used for testing anchors with bolt heads, but the project team’s chosen anchor was a headless helical friction anchor that could not ordinarily be gripped by standard ASTM test apparatus. Instead of pulling the anchor out of the limestone and the concrete wall, the team decided to pull the limestone off the anchor embedded in the concrete. To do this, the testing laboratory devised and fabricated “steel shoes” to hold the limestone panels that were then pinned to the concrete with the helical friction anchors extending through a hole at the bottom of the steel shoes. The steel shoes were then pulled off the concrete wall panel to mimic tensile loading in the anchors due to out-of-plane seismic loads or were pushed sideways to mimic shear loading in the anchors due to gravity loads.

Both cross-cut and vein-cut limestone panels were tested in shear and tension and, to account for edge distance of the anchors in varying sizes of full limestone panels or Dutchmen, 16-inch and 8-inch square panels were used for both tensile and shear tests. The compressive strength of the concrete slab panels used for testing matched the lowest compressive strength of the existing concrete walls. Before the tests, the concrete panels were manually cracked to achieve more realistic cracked concrete behavior.

The pattern for helical anchors installed in Dutchmen and partial size panel.

The pattern for helical anchors installed in Dutchmen and partial size panel.

Once enough tensile and shear tests were performed, results were presented to the Los Angeles Department of Building and Safety’s Building Research Section for approval. The coefficient of variation of the test results was determined to be high enough that the lowest measured capacity of the anchors was to be used as the appropriate anchor capacity. A factor of safety was then applied to the appropriate anchor capacity to determine the required number of anchors for each limestone panel.

Once the tensile and shear capacities of the helical anchors were determined, helical anchor patterns were designed for the weight and seismic load of each of the approximately 1,200 panels throughout the building façade. The patterns were selected based on the size of the limestone panels and Dutchmen. Depending on the location of the limestone panels, the anchors provide either out-of-plane restraint only, or both out-of-plane restraint as well as gravity support. At the former group of limestone panels, gravity support is provided by existing concrete curbs. Given the different anchor capacities for cross-cut and vein cut limestone panels, exterior elevations were prepared to map the type of each limestone panel across the existing façade. The types of panels were identified as vein-cut or cross-cut through close visual inspections of the natural voids in the existing limestone panels.

Anchors were installed through pilot holes drilled through both the limestone and concrete wall. Once countersunk, the final location of the anchors blends in with the natural voids on the limestone surface.

The newly restored façade.

The newly restored façade.

Conclusion

The limestone façade of the historic Saban Building was one of its most prominent features. The preservation of the façade in place of full replacement contributes to the building’s participation as a museum piece as well as the new home of the Academy Museum of Motion Pictures. The carbon footprint of the adaptive reuse project was significantly reduced with the preservation of the façade as opposed to a replacement scheme, and the falling hazard from damaged limestone panels was addressed through an innovative mechanism where the solution blends in with the natural feature of the façade.

Over 88 percent of the total historic surface area was retained and repaired, while only 12 percent was proposed for the replacement to match the original historic design. Of the original 1939 Texas Cordova Shelly Limestone, out of approximately 1,200 panels: 95.7 percent of panels were retained, cleaned, and repaired; 4.3 percent of panels were repaired by Dutchmen; 1.5 percent were replaced to match existing; and, approximately 40 percent of panels received minor mortar patch repairs. At the Steel Window Boxes and Frames, 100 percent of the panels were retained and repaired.■

A previous version of this paper was published in the 2019 SEAOC Convention Proceedings.


| AEC Magazine
2020.07.01 09:15

Image ArchiveHub lets users download and browse complete project data for handover, analysis or archiving

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| STRUCTURE magazine
2020.07.01 09:10

As I write this editorial, many communities and cities in the United States are just starting to “re-open” following the Coronavirus pandemic and shelter-in-place orders.  My firm, like most, transitioned into a full work-from-home situation in March with only minor issues and challenges.  Our business and employees have adapted remarkably well.  We are conducting meetings virtually through video calls, developing and reviewing construction documents by sharing data and models, accessing information through the cloud or virtually from our servers, and participating in new project interviews remotely.  Employees are doing their best to remain engaged and connected with one another.

The success with which we have transitioned into a remote company begs the question of why return to the old way of working in an office and why not maintain an entirely remote workforce?  Answering this question and planning for the future is not simple. For our industry, I do not believe we can assume that what we have done for the past three months can continue into perpetuity.  While it may sound appealing to eliminate a substantial portion of the real estate expense from our business and allow everyone to work remotely, I do not believe that is the future of the structural engineering office.  I believe we will come to the realization that our physical offices are important to the long-term health of our business and our employees.  However, I also believe that we will see a much larger fraction of our employees splitting time between the office and working remotely.  Below I offer thoughts on a few issues that I am considering with my firm and the reasons why I believe we will continue to have offices.

Electronic Connectivity – This is perhaps the most straightforward issue to address.  Clearly, the past few months have shown that technology solutions exist to allow the vast majority of our structural engineering work products to be completed remotely.  At my firm, we are planning to make additional investment in our connectivity and hardware needs to give employees the flexibility to work efficiently both in the office and remotely.  We believe this investment will pay off in productivity and engaged employees.

Training and Mentorship – As a professional services firm, much of what we do depends upon a highly-skilled staff that requires continuous training and development.  Some of that training comes from formal programs, but I believe the vast majority at my firm comes in the form of mentorship and interaction on projects.  Training also goes beyond technical work.  Our engineers learn how to interact with clients, deal with difficult situations, and communicate with each other by seeing their mentors and co-workers do it.  The personal experience and day-to-day immersion cannot be replicated over a video conference.  I believe that we still need to come together in our offices to develop future generations of structural engineers effectively and efficiently.

Mental Health – I have become more concerned about the mental health of my employees as we have extended remote working longer and longer.  As engineers, we have the stigma of being loners and anti-social.  In my experience, that is not true.  Our staff thrives on interacting with one another and enjoys the friendships that develop in the office.  I do not believe it can be replicated in a fully remote environment.  As engineers and as humans, we need interaction to maintain mental health.  During the first couple of months of remote working, our productivity was high. Still, I predict it will decrease the longer our employees are isolated and working in a fully remote environment.

Personal/Work-Life Separation – Before the pandemic, a frequent topic of discussion was personal/work-life balance. After three months of shelter-in-place and remote working, I am now hearing more about personal/work-life separation.  This has become particularly challenging for employees with young families.  While most employees are enjoying their ability to capture the time that would have been spent commuting to the office, I believe most will still want to return to an office for some of their work time, creating a physical and mental separation between personal and work life.

Flexibility – As we get beyond the Coronavirus pandemic, I believe we will be structuring our offices and work schedules for more flexibility.  At my company, I expect that most employees will return to working in an office, but we will also be providing more flexibility for them to work remotely.

Company Culture – Company culture is hard to define since every structural engineering company has its own.  At my company, the items I have discussed above contribute to our culture.  I do not believe our culture can survive long term with a fully remote workforce; it needs face-to-face interactions. A substantial contributor to how we have been able to survive and thrive, short term in a fully remote environment, has been our company culture and relationships built over years of face-to-face interactions.  In essence, I believe we are drawing from our culture bank right now, and we will eventually need to replace those resources.

As an answer to my own question, I believe we will maintain our offices, and I believe the majority of our employees at my firm will eventually want to return to the physical office with their co-workers, colleagues, and friends.  I also believe that we will need to provide the flexibility and tools necessary to allow our employees to balance their time between the office and remote work.■


| STRUCTURE magazine
2020.07.01 09:00

Key Considerations and Lessons Learned

Recent media coverage has highlighted the devastation associated with tornado outbreaks in many urban and suburban areas. Rapid population growth and urban sprawl in many cities within the central United States have increased the number of structures located within the potential path of these dangerous storms. Tornadoes generate high winds and extreme loads that are significantly higher than typical building design loads.

When tornadoes strike in populated areas, the cost can be devastating in terms of injuries, loss of life, and damage to property. The destructive tornado that struck Joplin, Missouri, in May 2011 injured 1,150 people, killed 158, and caused an estimated $2.8 billion in damage – one of the most expensive on record. In March 2020, a pair of devastating tornadoes passed through the Nashville, Tennessee, area, killing at least 24 people and severely damaging or collapsing hundreds of structures.

In 2014, the second edition of ICC 500, Standard for the Design and Construction of Storm Shelters, was co-published by the International Code Council (ICC) and the National Storm Shelter Association (NSSA). Starting with the 2015 International Building Code (IBC), certain structures are required to be designed with ICC 500-compliant community tornado shelters. This article provides clarity on when an ICC 500 tornado shelter is required per the IBC and shares lessons learned to help practicing structural engineers design safe and effective tornado shelters.

Tornado Rating Scale

It is helpful to have a baseline understanding of the Enhanced Fujita (EF) scale to comprehend the requirements of ICC 500. Within the EF scale, tornadoes are rated from EF0 to EF5 based on observed damage that is then correlated back to an estimated three-second gust wind speed. EF0 tornadoes start at an estimated wind speed of 65 mph and can cause damage, including loss of roof covering materials, gutters, awnings, or siding. An EF3 tornado has estimated wind speeds ranging from 135 mph to 165 mph, and damage may include failed roof structures and multiple collapsed walls. The most devastating tornadoes are rated EF5 and carry estimated wind speeds of 200+ mph. These tornadoes can cause complete destruction of engineered, well-constructed structures.

When is a Shelter Required?

Per IBC 2015, Section 423, ICC 500 tornado shelters are required for structures located within the region of the country designated with a 250-mph shelter design wind speed (Figure 1) that meet one of the following criteria:

Figure 1. Shelter design wind speed map for tornadoes. Ref: ICC 500-2014 Figure 304.2(1)

Figure 1. Shelter design wind speed map for tornadoes. Ref: ICC 500-2014 Figure 304.2(1)

  1. The structure contains critical emergency operations such as 911 call stations, emergency operations centers, fire, rescue, ambulance, and police stations.
  2. The structure is classified as a Group E Occupancy, such as a K-12 school, with an aggregate occupant load of 50 or more.

Design Criteria and Systems

ICC 500 tornado shelters must be designed for several types of extreme loads. The design standard requires that tornado shelters be designed to sustain wind loads five to seven times higher than a similarly sized, non-shelter building located on the same site. The minimum roof live load for a tornado shelter is 100 psf, up to five times higher than a non-shelter roof.

Storm shelters must also be designed for debris hazard loads, such as wind-borne debris and laydown, rollover, and collapse loading. For wind-borne debris loading, ICC 500 requires that all components on the envelope of a tornado shelter with a 250-mph design wind speed be tested to resist a 15-pound sawn lumber 2×4 missile shot at a speed of 100 mph for vertical surfaces and 67 mph for horizontal surfaces. FEMA P-361, Third Edition, Part B8, is a helpful reference for practicing engineers to clarify debris impact loading and determine minimum wall and roof thicknesses that meet these requirements.

Another type of debris hazard load is laydown, rollover, and collapse loading; however, little code guidance is provided to assist practicing engineers when calculating the magnitude of these loads. Generally, these hazards are defined as structures or components that have a fall radius overlapping the footprint of the shelter. Based on the verbiage in ICC 500, structural engineers must rely on judgment to determine these significant and potentially catastrophic loads. At a minimum, it is recommended the shelter be designed for the weight of any laydown, rollover, or collapse hazard multiplied by an impact factor, the magnitude of which is left up to the engineer’s judgment. Without further code guidance, the authors believe it is prudent to consider an impact factor of no less than 2.0. Further guidance on this topic is being considered for inclusion in the 2020 version of ICC 500.

When determining the best structural system for a tornado shelter, the size of the shelter has a significant impact. For smaller shelters, such as those commonly located in municipal facilities with emergency operations functions, fully grouted concrete masonry unit (CMU) walls may be the most economical option. For these shelters, a roof system composed of structural steel beams and concrete-topped composite metal deck has proven to be cost-effective. However, designing connections to transfer the large roof beam reactions directly into the CMU walls can become difficult. Detailing a concrete ring beam around the perimeter of the shelter roof, integral with the CMU wall, has been a successful way to facilitate more effective steel beam connections to the walls (Figure 2).

Figure 2. Typical concrete ring beam detail.

Figure 2. Typical concrete ring beam detail.

For larger shelters, commonly located in K-12 schools, concrete walls are frequently required. A cost consultant should be engaged to provide preliminary cost estimates to help guide the decision regarding which type of concrete wall system would be most economical for a given project. Total precast concrete solutions can also be an economical solution for larger shelters; however, special detailing must be provided at the precast panel joints, and the diaphragm design and connections require careful coordination with the precast engineer. If pursuing this option, a precast manufacturer should be retained to consult on the project during the design phase.

Lessons Learned

Having experience with both municipal and educational projects, the authors’ firm has designed many ICC 500 storm shelters. As a result, the following list of lessons learned may help practicing engineers as they navigate through these provisions.

First, it is wise to purchase a copy of the ICC 500 standard with the commentary included and download a free copy of FEMA P-361, Design and Construction Guidance for Community Safe Rooms. Both documents provide helpful guidance and context for many of the provisions in ICC 500.

Overall Project

  1. Ensure the Owner engages a peer reviewer early, and ensure the architect builds time into the project schedule to account for the peer-review process. Within ICC 500, an independent peer review is required for all storm shelters that are mandated by IBC 2015. Reviews are required for structural, architectural, and MEP systems, and many times structural calculations are requested by the peer reviewer. Shelter peer reviews commonly take two to three weeks, and the authors have found success scheduling the peer reviews in conjunction with the 50% Construction Documents (CD) and 90% CD deadlines. A signed peer review report must be submitted to the authority having jurisdiction (AHJ) before the issuance of a building permit, so allowing adequate time for peer review is essential to maintaining the project schedule.
  2. Encourage the architect to clarify the occupant load for the storm shelter early. In essence, the occupant load requirements can be widely interpreted by AHJ’s for both municipal and educational projects, and the size of the shelter is significantly affected by that decision as the minimum size is dictated by occupant load.
  3. Encourage early study and comprehension of the Quality Assurance (QA) plan requirements by the full design team. ICC 500 requires that a QA plan be developed and included within the construction documents. This plan must identify all main wind force-resisting systems and wind-resisting components along with the observations, special inspections, and testing requirements for these elements. In addition to structural elements, there are architectural and MEP components that fall within the scope of the QA plan.

Structural

  1. Drawing organization is critical – separate storm shelter and non-shelter requirements on notes, special inspections, plans, and details to keep the shelter requirements clear.
  2. Provide an expansion joint around the perimeter of the shelter and avoid supporting elevated framing on top of single-story shelters.
  3. Include wall elevations for all perimeter shelter walls on drawings and closely coordinate all architectural and MEP penetrations. Check the capacity of opening jambs early, as jamb capacity often governs the design.
  4. Design the shelter for an internal pressure coefficient of GCpi = +/−0.55 when calculating wind loads, unless atmospheric pressure change (APC) venting is provided to justify an enclosed building coefficient of GCpi = +/−0.18. In the authors’ experience, providing APC venting is challenging and generally not relied upon.

    Figure 3. Baffling system example.

    Figure 3. Baffling system example.

Architectural/MEP Coordination

  1. Coordinate with the architect and MEP engineers to ensure missile impact test data has been obtained for all opening protective devices such as doors, windows, and louvers. If a qualified component is not available, then a baffling system must be provided; the design of this frequently falls within the structural engineer’s scope. See Figure 3 for a simplified depiction of a baffling system for a wall penetration; remember that the storm debris trajectory must hit two missile impact resistant surfaces before entering the protected occupant area.
  2. Coordinate with the architect and MEP engineers to ensure conduit, electrical boxes, fire extinguishers, and/or other components are not embedded in perimeter shelter walls such that they compromise the minimum wall thickness required to meet the impact resistance requirements.
  3. Coordinate with the mechanical engineer to determine if the shelter will be naturally or mechanically ventilated since this will affect the size and quantity of penetrations through the envelope of the structure.

Construction

  1. Develop a standard form to help guide contractors in submitting “Contractor’s Responsibility” statements; it is not common practice in many jurisdictions. ICC 500 requires that all contractors responsible for the construction, fabrication, or installation of any item listed in the QA plan submit a written statement of this responsibility that acknowledges the special requirements and quality control measures they will undertake. These written statements of responsibility must be submitted to the AHJ, the responsible design professional, and the Owner before the commencement of any work.
  2. Require a pre-construction meeting specifically for the storm shelter and include an agenda for this meeting within the project specifications.
  3. Ensure the third-party testing lab is engaged in all conversations related to storm shelter inspections early – they are the eyes and ears on-site in many cases.
  4. Require a partial-wall CMU mock-up before the start of overall construction if the shelter perimeter walls are CMU, as this generally results in a much higher quality of construction.
  5. Consider incorporating qualification-based selection criteria for certain key subcontractors to ensure prior experience with ICC 500. A contractor’s previous experience on an ICC 500 storm shelter increases the level of quality dramatically.

Summary

When working on a project with an ICC 500 tornado shelter, strive to engage clients early in discussions about storm shelter requirements. Encourage clients to build additional time into the project schedule for peer reviews and to plan for additional costs in the scope-to-budget phase. Costs associated with a more robust structure and foundations, specialty architectural and MEP components, and emergency MEP systems can add up quickly. Lastly, structural engineers should expect to help lead a more detailed coordination effort during the design and construction stages. Those steps, coupled with a thorough understanding of both ICC 500-2014 and IBC 2015, will aid in a smoother design and construction process resulting in a storm shelter capable of withstanding catastrophic weather events.■

Previous articles on ICC-500:

Tornado Shelters in Schools. Harris, STRUCTURE September 2016

Hurricane-Driven Building Code Enhancements. Knezevich et al., STRUCTURE July 2017

Tornado Debris and Impact Testing. Throop et al., STRUCTURE May 2018


| STRUCTURE magazine
2020.07.01 08:50

Canopies can either be free-standing structures or can be attached as a structural component to a main building structure. They can be situated at an entrance of the building, acting as awnings, or they can be located anywhere along the face of the building up to the roof level. Canopies are not only used for protection of the entrance from dust and rain but also to increase the aesthetic appeal of the overall structure by either becoming integrated into the building or by highlighting it. Hence, there is a need to economically design the size and shape of the canopy and its connections.

Codes governing canopies provide limited information dedicated to the design of canopies. For example, the American Society of Civil Engineers’ ASCE 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, does not differentiate between the different types of canopies and recommends that canopies be designed as “Components and Cladding” structures for wind loads. Without accurate guidelines, structural engineers often overestimate loads acting on canopies and design components with increased size, which may often lead to space constraints and reduce the aesthetic appeal of the overall structure. ASCE 7-16 provides a dedicated section for canopy design for buildings with an overall height of less than 60 feet; however, it does not provide for canopy design for high-rise building structures.

This article discusses the effect of wind loads on the canopy systems and provides special considerations and precautions that need to be taken when designing such systems. Here, canopy systems can be defined as the components related to the canopy itself, to its connections to the wall, and the wall connections to the foundation. This discussion indicates the need for a distinction between the design criteria of canopies for low- rise buildings and for high-rise buildings.

Canopies

Canopies are the structures attached to the main structure or buildings, which are often subjected to dynamic loads such as wind, seismic, and snow. These load combinations predominantly govern the design. ASCE 7-16, for buildings not exceeding 60 feet in height,  considers an upper surface pressure and a lower surface pressure on a canopy, acting individually in one case and acting simultaneously in a second case, where these two loads are combined to obtain a net pressure on the canopy.

ASCE 7-16 does not provide separate provisions for the design of canopies for high-rise buildings, and that often leads to a conservative approach of overestimating loads. This overestimation of loads happens when trying to determine uplift forces caused by wind loads.

Codes have not yet considered the effect of wind for the design of canopies attached to tall buildings. Structural engineers have been left to apply the same principles of design for both low-rise and high-rise buildings. The location of canopies and the shape of buildings are also critical aspects of design. Canopies situated at the corner of  L-shaped or irregular buildings would see an increase in upward wind loads due to the torsional effect of wind at corners. The height of the canopy and the height of the parent wall of the building (i.e., the building wall to which the canopy is attached) is a significant contributing factor in estimating the downward pressure acting on the canopy.

The upper surface pressure on a canopy is a direct downward force on the top of the canopy.  This occurs when the wind is obstructed by the face of the wall and travels along the face of the wall, causing a downward force on the canopy. Lower surface pressure is often a combination of uplift caused by the wind and roof uplift (suction) acting on the canopy, which results in an upward force on the canopy. Sometimes, both loads can act simultaneously and result in a combined net pressure acting on the canopy.

For a relatively typical rectangular building, the key difference between canopies for short buildings and high-rise buildings is that, for short buildings, canopies are often at or near the roof level. This makes the attached canopy a part of the roof system and has to be designed for roof uplift pressures as well. However, for high-rise buildings, the parent wall of the building is much taller than for short buildings, which increases the downward force acting on the canopy, as shown in Figure 1. This consideration is significant because engineers often assume greater lower surface pressures and underestimate the downward forces for high rise buildings.

Figure 1. Differing wind pressures between short buildings and high-rise buildings.

Figure 1. Differing wind pressures between short buildings and high-rise buildings.

A canopy is often suspended or supported by cables attached to the free end of the cantilever member of the canopy, as shown in Figure 2. The use of a cable system is preferable by architects because of its aesthetic appearance. However, it is a drawback because cables are not capable of resisting compression loads or moments, although they are suitable for resisting tension loads.

Figure 2. Illustration of a typical canopy connection to the wall.

Figure 2. Illustration of a typical canopy connection to the wall.

Structural engineers generally prefer pipe systems in place of cable systems to mitigate some of these drawbacks. But in most cases, pipe sections are expensive to install and aesthetically not preferred. Instead of relying on a cable to resist the compression force, which it cannot, the canopy end connection to the parent wall is designed such that it resists the moment caused by the upward pressures as well as the downward pressures, as shown in Figure 3.

Parent Wall Design

Precautions must be taken such that the parent wall can resist the moment forces transmitted by the connection. The wall is often thin and may not be capable of resisting excess moments from the canopy connection reactions. Thus, additional vertical reinforcement can be provided near the tension face of the wall (generally at the inner face of the wall if the connection is made to the outer face or vice versa) to resist the tension caused by the moment acting on the wall, as shown in Figure 3. The reinforcement must be placed along with the typical wall vertical reinforcement before placing the wall. The length of the reinforcement provided must at least exceed the development length required.

Figure 3. Illustration of the location where additional reinforcement is required.

Figure 3. Illustration of the location where additional reinforcement is required.

As an alternate procedure, the moment due to the wind loads can be distributed over a length of the wall with the help of the stiffener plates or angles. The stiffener plates could transmit the forces from the moment couple over the length of the wall, thereby reducing the concentration of stresses over a small section.

Member Design

There is always a limit on the size of the canopy framing members.  The main cantilever beams that resist the wind loads need to have sufficient size and thickness to resist the moment caused by wind loads. For this situation, a tapered cantilever beam with varying depth works very well. The cantilever depth can increase linearly from the free end of the member to the supported end, providing the required moment capacity.

Most canopies are mono-sloped; as such, the upward forces increase when the slope increases above 30 degrees.  No significant increase in upward wind forces has been observed until the slope of the canopy reaches 30 degrees [Suárez, 2012]. If the canopy is situated at the corner of a building, more wind gets trapped underneath the surface of the canopy, thus exerting an upward pressure.

Foundation Design

The parent wall-to-foundation dowels must not only be designed for compression loads caused by the weight of the wall but also must be designed for tension loads, lateral loads, and over-turning moments caused by the canopy moment connection to the face of the wall. Also, the eccentricity of the embed plates, used for the canopy connection to the face of the wall, must be considered in the design of the foundation wall dowels.

Surface Cladding Design

Many canopy systems in buildings are now designed to accommodate glass cladding at the top surface. These glass cladding systems are extremely sensitive to the slightest deflections. These member deflections are often limited to a Span Length (in inches)/480 ratio (i.e., L/480).  The glass panels are often subjected to both downward and upward pressures, which can create fatigue in the glass if not uniformly supported by the framing system members, resulting in localization of stresses.

The design of canopy framing members must consider deflections such that they will be within tolerable limits.  Side sway deflections in the members caused by wind or seismic forces are often ignored by structural engineers but must be considered, especially when the cladding on the top of the canopy is glass.

Cable Design

A cable with an angle greater than 45 degrees with the horizontal provides the most favorable condition to resist the downward forces or tension forces caused by wind. Also, the connection at either end of the cable is always pinned.

Conclusions

It is important to understand code provisions for canopies, as engineers often underestimate the upper surface loads, overestimate the lower surface loads, and usually design for excessive uplift forces. Consideration of issues involved with pipe and cable support systems also are essential to adequate design.■

References

  1. Candelario Suárez, J. (2012). Wind-Induced Pressures on Canopies Attached to the Walls of Low-Rise Buildings. Masters. Concordia University.
  2. Roh, H., and Kim, H. (2011). Wind pressure distribution on canopies attached to tall buildings. Journal of Mechanical Science and Technology, 25(7), pp.1767-1774.
  3. Paluch, M., Loredo-Souza, A., and Blessmann, J. (2003). Wind loads on attached canopies and their effect on the pressure distribution over arch-roof industrial buildings. Journal of Wind Engineering and Industrial Aerodynamics, 91(8), pp.975-994.

| STRUCTURE magazine
2020.07.01 08:40

Viscoelastic Coupling Dampers

Tall building designers are increasingly facing challenges related to wind and earthquake-induced vibrations, especially as buildings are built taller and more slender. Frequent windstorms can cause lateral accelerations, which can result in occupant discomfort. Rarer, more severe windstorms and service level earthquakes (SLE) produce large loads in the structure that have to be resisted elastically by the structural members. A primary cause of these vibrations is the low levels of inherent damping (the ability of structures to absorb vibrational energy and slow down dynamic vibrations) in taller structures. Furthermore, severe earthquakes can cause distributed damage throughout the entire structure in conventionally designed buildings, putting in question their post-earthquake safety and use.

Damping Systems

Damping systems for tall buildings are classified as distributed damping systems (typically viscoelastic or viscous) or vibration absorbers (typically tuned mass dampers or tuned sloshing dampers). Vibration absorbers are large masses at the top of buildings that, when “tuned,” transfer a portion of the energy from the building structure to the vibration absorber. These systems are only tuned to the fundamental lateral modes of vibration and are typically only relied on for reducing frequent wind vibrations. This is due to their reduced effectiveness beyond their tight-tuning range and because of maintenance requirements, such as monitoring water levels or checking waterproofing for a tuned sloshing damper or inspection of mechanical components in tuned mass dampers. The most significant overall impact on a project is that they occupy large valuable space at the top of buildings.

Distributed viscoelastic and viscous dampers are activated through relative movements induced between structural members when a structure sways under wind or earthquake loading. When they are optimally configured and designed, they can increase damping levels in building structures in both fundamental and higher modes of vibration and thus be effective for all dynamic loading conditions.

Viscoelastic Coupling Dampers (VCDs)

Distributed dampers have historically been configured in shear-type frame buildings either as braces or vertical damping panels, which are engaged by inter-story racking of the structure. This is efficient and practical for low rise steel frame buildings, but today’s tall and slender reinforced concrete (RC) buildings behave more like cantilevers under lateral loads. The lateral load resisting systems of tall buildings are now primarily formed by vertical structural elements coupled together with coupling beams or outriggers, which are deformed and stressed in vertical shear. Those heavily stressed coupling members are ideal locations to configure dampers to add distributed damping to high-rise buildings to reduce wind and seismic vibrations. These features led to the development of the Viscoelastic Coupling Dampers (VCDs) at the University of Toronto in collaboration with Nippon Steel Engineering and Kinetica (Figure 1).

Figure 1. Viscoelastic coupling dampers.

Figure 1. Viscoelastic coupling dampers.

VCDs consist of multiple layers of solid viscoelastic (VE) material sandwiched between and bonded to multiple steel plates. Each consecutive steel layer is extended out, connected to the opposite side, and anchored to the structure. As buildings deform due to lateral vibrations, the solid VE material layers are sheared in-between the alternating consecutive steel plates, providing instantaneous elastic and viscous forces. VE material can be modeled simply as a spring and dashpot in parallel. The force in the VE material, FVE (t), at a time, t, is expressed as FVE(t) = kVE uVE(t) + cVEVE(t), where uVE(t) and VE(t) are the shear deformation and deformation rate, respectively, at a time t, while kVE and cVE are the VE material stiffness and damping coefficients. Figure 2 shows the deformed shape of a coupled tall building with the solid VE material being sheared vertically and dissipating lateral vibrations.

Figure 2. Coupled wall tall building structural kinematics.

Figure 2. Coupled wall tall building structural kinematics.

Because the solid VE material is rigidly connected to the structure and the damping mechanism does not rely on mechanical components or pins, the solid 3M™ VE material dissipates energy at the molecular level. It, therefore, provides instantaneous viscoelastic response even for very small deformations. Tests conducted at the University of Toronto showed that the solid 3M VE material used in the VCD provided a viscoelastic response even for deformations of +/-0.003mm or +/- 0.00011 inch. In seismic areas, where the building could be subjected to a rare earthquake, whereby drifts can become very large as the amplitude of vibrations is increased, the connecting steel members are capacity designed to yield. This adds even more energy dissipation, and capacity protects the remaining structure. This unique feature allows the damper to be used efficiently for all loading scenarios, frequent windstorms, severe windstorms, and frequent earthquakes through to Maximum Credible Earthquakes (MCEs).

The solid 3M viscoelastic material was the first damping material used in structural applications dating back to 1969 and has been utilized in 300 buildings in some of the world’s most severe wind and seismic regions. There is no requirement for maintenance or monitoring because of the excellent aging and fatigue characteristics of the 3M VE material.

Figure 3. Full-scale uniaxial and shear racking VCD tests at the University of Toronto.

Figure 3. Full-scale uniaxial and shear racking VCD tests at the University of Toronto.

At the University of Toronto, the 3M VE material has been thoroughly tested to confirm its mechanical properties, which agreed very well with the manufacturer’s stated properties. Also, multiple full-scale VCD test specimens, manufactured by Nippon Steel Engineering, have been tested uniaxially, confirming the scalability of the material properties. Multiple full-scale VCDs have been tested in two different racking configurations to confirm the overall system performance (Figure 3).

Examples of Design with VCDs

The following are projects where structural engineers have used the VCDs to create value for their clients, in wind-critical regions, seismic-critical regions, and combined wind and seismic-critical regions throughout the world. In all instances, the VCDs have allowed engineers to meet design targets economically and improve the dynamic performance of the structure. All buildings were designed and analyzed using typical commercial software, such as ETABS, SAP2000, or Perform-3D. Linear springs and dashpots were used to model the mechanical VE damper behavior. Every VCD project has a robust QA/QC program provided by the damper manufacturers, Nippon Steel Engineering and 3M, including VE material tests and full-scale VE damper panel production tests.

YC Condominiums, Toronto, ON

Yonge College (YC) Condominiums is a 66-story, slender residential tower (11-to-1 slenderness) in downtown Toronto, where limiting wind vibrations caused by frequent windstorms was a crucial aspect of the structural design. The developer’s mandate for the project was to maximize sellable space within the prescribed architectural height, which determined the choice of damping system for the project.

Figure 4. VCDs in Yonge College condos.

Figure 4. VCDs in Yonge College condos.

In the narrow plan direction, which was critical for lateral vibration, the lateral load resisting system consists of two primary coupled RC shear walls, along with an RC core and columns (Figure 4). Wind tunnel studies indicated that the building would require a supplemental damping system to be added to increase the damping in the fundamental mode of vibration to improve the level of human comfort for 1 in 1-year and 1 in 10-year wind-induced motions. Two damping systems were considered: i) distributed Viscoelastic Coupling Dampers (VCDs) and ii) a bi-level Tuned Sloshing Damper (TSD) tank. The building developer selected the VCDs for the project after a detailed comparative technical and financial analysis of the two systems. A primary advantage of the VCDs was the fact that they were integrated within the structural system, resulting in an additional 5,000 square feet of usable penthouse real estate. Another consideration was that there was no tuning or monitoring, and there was no long-term maintenance plan required for the VCDs to ensure performance.

Figure 5. Damped VCD outrigger configuration.

Figure 5. Damped VCD outrigger configuration.

The structure used 84 identical modular Viscoelastic coupling damper panels, produced by Nippon Steel USA and 3M. Each VCD consisted of 2-VE damper panels bolted to cast-in-place steel embeds. A total of 42 VCDs replaced 42 RC beams on 21 levels of the structure. Figure 5 shows the implementation of the dampers in the project. During erection and concrete casting, temporary steel channels were used where the dampers were to be installed to ensure the correct VCD placement. After the building envelop was completed, a small three-person crew of ironworkers removed the channels and installed the VE damper panels with a slip-critical bolted connection. Drywall was then installed over the VCDs.

Figure 5. Damped VCD outrigger configuration.

Figure 5. Damped VCD outrigger configuration.

The wind tunnel results required an added 0.9% damping in the fundamental mode of vibration. Each VE damper panel consisted of nine (9) VE material layers, each 5mm-thick, bonded between the steel plates. The VE dampers were modeled with a spring and dashpot in parallel and configured into the Engineer of Record’s (EOR) ETABS models. The added damping was assessed using free vibration analyses. Free vibration is readily implemented by inputting a lateral push to the building, holding it there, and releasing the load, and then measuring the reduction in peak cycle amplitude over multiple cycles of vibration.

During construction, the dynamic characteristics of the structure were monitored with accelerometers as the project progressed; localized displacement measurements of the dampers were also taken to study the robustness of the damping system and to compare the in-situ building behavior to the models. Monitoring showed that the predicted added damping was slightly exceeded during a service level event (5-year return period). Also, the kinematic behavior predicted by the EOR’s ETABS models was accurate even though the building period was shorter than that considered for the wind tunnel studies, and the peak modal amplitude of vibration during the storm was only 80 mm (approximately 3 inches).

Outrigger VCD Configuration

Recently, the VCD system was used in south-east Asia in nine tall buildings (Park Central Towers 1 and 2, Seasons Residence Towers A, B, C and D, Connors Tower, and ParkLinks Towers 1 and 2), where the VCDs are intended to improve both the wind and seismic response of the structure. The general design approach in these areas is to conduct a conventional code design for wind and non-prescriptive performance-based design using the PEER-TBI and the Los Angeles Tall Buildings Structural Design Council (LATBSDC) guidelines. Because of the significant wind demands, outrigger flag walls are commonly used to increase the stiffness of the lateral load resisting system to reduce wind drifts. The flag walls consist of heavily reinforced concrete beams spanning over the corridors and framing into an RC wall that runs between two residential units. During rarer design level events, such as service earthquakes and design windstorms, the RC beams are designed to remain linear elastic; during rare earthquakes, those RC beams are designed as structural fuses to prevent overload of structural columns and outriggers. Because of this design intent, the beams end up being very strong to resist wind loads; during MCE events, they introduce large shear forces into the core and large axial forces in the columns. The beams are expected to be mostly damaged because of the significant combined axial and shear demands.

VCDs are introduced connecting the RC flag walls to the columns with ductile detailing of the steel connecting elements, following general requirements prescribed in ASCE-341, Seismic Provisions for Structural Steel Buildings, seismic details for Eccentrically Brace Frames (EBF) steel links. The flag walls and columns are capacity-designed to accommodate expected overstrength in the ductile members (Figure 5). A slotted connection is provided in the damper panel connection to allow for differential settlement between the core and the columns if required. Under more frequent windstorms, the dampers add significant damping to the system and reduce drifts. Under design level wind or service level earthquake events, where the structure is intended to respond linearly elastic or essentially elastic, loads are reduced, resulting in structural efficiencies. Under more extreme events such as Maximum Credible Earthquakes (MCE), the ductile connecting elements can yield reliably, ensuring columns, flag walls, and corridor beams are not damaged. This results in reduced loads on the RC core and columns because of the added damping and a gentler stiffness transition compared to the RC flag walls. It is also a more reliable ductile mechanism compared to the conventional flag wall RC beams. In addition, because of the increased wind and earthquake performance, a number of developers have also advertised the use of the VCDs to emphasize higher structural performance, garnering an estimated 5% additional revenue.

630-meter Seismic-Critical Building in Southeast Asia

A 110-story, 630-meter mega tall building, with a total gross floor area of more than 330,000 square meters designed in a highly seismic region in Southeast Asia, has been redesigned with the VCDs (Figure 6).

Figure 6. Megatall building equipped with VCDs.

Figure 6. Megatall building equipped with VCDs.

Even though it is a mega tall structure, the design of the building was governed primarily by seismic loading using a non-prescriptive performance-based approach with PEER-TBI and LATBSDC guidelines. The primary lateral load resisting system consists of a coupled core wall (RC) and a steel truss outrigger system that connects the core with the super columns. There is a secondary lateral load resisting system consisting of a mega frame comprised of the super columns and belt trusses along with the steel truss outrigger system.

Due to the importance of the tower in the region, size of the tower, and seismicity of the site, there was a desire to improve seismic performance and reduce the cost of the lateral load resisting system. Two design challenges included the large core shear forces requiring significant reinforcing and large overturning moments requiring extremely deep mat foundations. The redesign consisted of the VCDs replacing about 60% of the diagonal RC coupling beams in the core throughout the height of the building, with the VCDs locations optimized for performance with Perform-3-D results targeting the large shear forces and overturning moments. The VCDs provide significant levels of added damping in the first modes of vibration, which reduces the overturning moments. The VCDs also provide added damping in the higher modes of vibration, which reduces the core shear demands significantly. The upfront financial benefits are substantial, with a significant reduction in structural materials and approximately 6 months of expected construction time savings primarily because of reduced complexity of the reinforcing and member size reduction. In addition, because of the added damping and the fact that the VCDs are replacing structural members that are expecting to be heavily damaged during an MCE event, the VCDs inherently increase the resilience and expected damage for all earthquake levels. Also, the use of the VCD enables the developer to market the resilience improvements that are achieved, which is expected to result in increased property value and revenue.

Looking Forward

Tall building design is continuing to evolve, and the VCD is a tool that structural engineers can use to solve dynamic loading challenges as designs push new limits. As a robust wind and earthquake damping system, VCDs can be readily implemented by using tall building structural design tools such as commercial software platforms, wind tunnel testing, and performance-based design, resulting in significant structural performance and cost-effectiveness of high-rises.■

Structural Engineer Project Teams

ARUP, Magnussen and Klemencic Associates (MKA), PT Gistama, Read Jones Christoffersen (RJC), SY^2, and Thornton Tomasetti (TT).


| STRUCTURE magazine
2020.07.01 08:30

What is it, and how is it implemented?

The recent publication of the ASCE/SEI Prestandard for Performance-Based Wind Design (Prestandard), and the upcoming publication of a Manual of Practice on Design and Performance of Tall Buildings for Wind prepared by an ASCE/SEI Task Committee, make this an apt time to provide an overview of the intent of these documents, the present state-of-the-art in Performance-Based Wind Design (PBWD), and current efforts to update knowledge.

The Prestandard, in its first edition, provides a roadmap to achieving the wind performance objectives specified by ASCE 7 for structural loads and building envelopes while working outside of common prescriptive procedures. The document was compiled by a working group comprised of structural engineers, building envelope engineers, wind engineers, and academics to provide a wind engineering document to complement the PEER TBI Guidelines for Performance-Based Seismic Design of Tall Buildings. The overall goals of PBWD are to allow more efficient designs that meet performance targets for building functionality while reducing property damage from wind events. The Prestandard provides a set of procedures that can be followed to show compliance with performance objectives for both strength and serviceability in design. It is laid out with the commentary interspersed among the normative text, a move that was made due to the unique nature of the content and in recognition that some areas still require further research before they can be widely applied.

Figure 1. Rainier Square, Seattle – a test case for performance-based design approaches. Courtesy of Magnusson Klemencic Associates / Michael Dickter.

Figure 1. Rainier Square, Seattle – a test case for performance-based design approaches. Courtesy of Magnusson Klemencic Associates / Michael Dickter.

The Main Wind Force Resisting System (MWFRS) portions of the Prestandard are focused on tall buildings (such as that shown in Figure 1). Tall buildings are the class of structures that have the most potential to benefit from PBWD by allowing some inelastic deformation of limited portions of the structural system under extreme wind loads. The chapter on building envelopes, though, is targeted towards all types of buildings where superior performance is required in extreme wind events, such as hospitals, data centers, and other buildings requiring post-disaster functionality. Apart from the building envelope provisions, all applications of PBWD require wind tunnel generated building-specific wind loading inputs.

The Prestandard provides clear minimum performance objectives and acceptance criteria, with associated mean recurrence intervals (MRIs), for different risk categories of buildings. The performance objectives and associated acceptance criteria are provided for Occupant Comfort, Operational and Continuous Occupancy, Limited Interruption performance objectives for the MWFRS, the building envelope, and nonstructural components and systems.

The Occupant Comfort and Operational performance objectives are evaluated using traditional linear elastic design approaches. The Operational performance assessments consider drift limits and, importantly, a Deformation Damage Index (DDI), which is a more representative technique for the assessment of racking deformation that is the primary source of damage to internal nonstructural components.

Non-Linear Time-History Analyses (NLTHA) may be utilized for the Continuous Occupancy, Limited Interruption case, to demonstrate that performance objectives are met. The Prestandard outlines three methods by which this can be achieved.

  • Method 1 is a deemed-to-comply method based on engineering experience and judgment.
  • Method 2 is based on NLTHA of the structure, followed by a conditional probability reliability assessment of the design. This method provides a slightly more prescriptive approach on how to use NLTHA to validate the design but also recognizes the limitations in current knowledge that may limit its practical use at present.
  • Method 3 is based on NLTHA of the structure in conjunction with a dynamic shakedown analysis to evaluate the reliability of the structure. A dynamic shakedown analysis is a very computationally efficient approach that can be applied to PBWD by allowing probabilistic assessment using many time-histories.

Three types of wind tunnel tests are commonly used for the determination of overall wind loads and responses of tall buildings: High-Frequency Pressure Integration (HFPI), High-Frequency Balance (HFB) testing, and aeroelastic testing. The first two of these are what are known as aerodynamic models; they measure the external wind loads applied directly to the model with the dynamic responses calculated analytically after testing. Aeroelastic testing incorporates the structural dynamic properties into the wind tunnel model and directly measures load effects and responses.

One of the critical elements of PBWD for the structural system is optimizing the Demand-Capacity Ratios (DCRs) of individual key structural components. The techniques that can be used for this are similar to those that have been used in long-span roof analyses where pressure time-histories can be applied directly to the structural model based on areas of influence, or influence coefficients can be provided by the structural engineer to allow the wind engineer to quantify critical load effects in members. Of the three test types described above, only the HFPI approach is amenable to an easy application for PBWD. The HFB approach uses the wind tunnel model as a mechanical integrator with the applied loads measured at the base. While this is a very accurate approach in terms of the overall loads, it does not provide a direct measurement of the distribution and correlation of excitation forces over the height of the building. For many buildings designed using traditional approaches, this is of limited importance. With tall, slender buildings, the overall load effects may be dominated by resonant response, which is a function of the mass distributions and mode shapes.

For PBWD, however, it is necessary to know the distribution of the applied loads. Load distribution can only be measured directly using HFPI. This requirement leads to one of the limitations of the approach. For very tall and slender buildings, especially those with complex geometry, it is not always possible to physically fit sufficient pressure tubes into the wind tunnel model to accurately capture the simultaneous pressure distributions over the entire building. These very slender buildings are also the type where aeroelastic testing may be needed to capture aerodynamic damping effects. Therefore, composite approaches are likely to be required for particularly tall and slender buildings.

Unlike seismic loading, critical wind loads can result from uncorrelated excitation mechanisms in multiple directions. For many of the tall buildings for which the use of PBWD may be most valuable, the peak responses may result from cross-wind excitation (also referred to as vortex shedding) combined with along-wind buffeting. The rates at which the building responds to each of these phenomena with increases in wind speed are not proportional, and, in the case of cross-wind response, may exhibit peaks at less than the design wind speed. The correlations between wind speed and response can also vary widely with even small changes in wind direction. Examples of this variation are shown in Figure 2, where the base moment responses about orthogonal axes are indicated for two wind directions for a tall, slender building. The cross-wind response is particularly distinct about the x-axis for a wind direction of 310 degrees, where a vortex-shedding peak can be observed at a reference wind speed of around 24 m/s, after which the response reduces, before increasing again at higher wind speeds. Consequently, calculating the total probability of exceedance is much more computationally intensive for wind effects than for seismic effects due to the wide variation in building responses to wind.

Figure 2. Graph of along-wind and cross-wind responses for a tall, slender building for different wind directions.

Figure 2. Graph of along-wind and cross-wind responses for a tall, slender building for different wind directions.

Recognizing that we currently have minimal experience with the application of PBWD principles to design, a research effort is being conducted under the auspices of the ASCE 7 wind loading subcommittee. Multiple structural engineering firms developed designs for three standardized buildings located in two different wind climates representing New York and Miami. The three buildings are prismatic with two tall towers and one shorter, less dynamically sensitive building. Pressure time-histories for the buildings were measured in the wind tunnel and will be made available as open-source for reference. Figure 3 shows one of the buildings, the classical CAARC building that has long been used as a reference structure for calibrating and comparing wind tunnels, being tested using both the HFB and HFPI techniques.

Figure 3. Standardized CAARC models in the wind tunnel: High-Frequency Balance Model (left) and High-Frequency Pressure Integration model (right). Courtesy of CPP Wind Engineering.

Figure 3. Standardized CAARC models in the wind tunnel: High-Frequency Balance Model (left) and High-Frequency Pressure Integration model (right). Courtesy of CPP Wind Engineering.

The structural engineers did their preliminary design using codified approaches. The dynamic properties from these designs were then used in a typical linear elastic analysis using wind tunnel data to provide updated loads with which the designs were refined. This process followed the typical pattern of wind tunnel testing. A set of results for one set of structural properties is shown in Figure 4, which demonstrates good agreement between the HFB and HFPI approaches. Figure 4 also shows the dominance of the cross-wind responses, at 0° and 180°, relative to the along-wind responses, at 90° and 270°, for an isolated, prismatic tall building of relatively modest slenderness. The structural models and associated pressure time-histories were provided to Dr. Seymour Spence and his research team at the University of Michigan. They are currently subjecting the models to shakedown analysis, consistent with Method 3 of the Prestandard, to investigate the DCRs of individual members and to determine the critical governing load cases, e.g., serviceability deflections, accelerations, or member strength capacity.

Figure 4. Comparison of high-frequency balance and high-frequency pressure integration results for CAARC model.

Figure 4. Comparison of high-frequency balance and high-frequency pressure integration results for CAARC model.

Given the novelty of PBWD, all parties involved in the design and approval of buildings designed using PBWD approaches must be fully aware of the limitations, the risks, and the ramifications of the use of alternate methods. Consequently, independent peer review by qualified professionals is required when using this approach. In these early days, peer review is expected to be extensive and conducted by a team of reviewers with individual specialties. The local Authority Having Jurisdiction (AHJ) should also be involved from early in the decision-making process to ensure that design methodologies and reviews will be acceptable to them. To assist in this process, the Prestandard has a full chapter on peer review expectations, including scope of work and guidance on dispute resolution.

As can be concluded from the discussions above, PBWD may not yet be ready for everyday application. The Prestandard has been written with this in mind and specifically highlights current limitations. Significant progress is, however, being made to create a framework for its use and to fill in the gaps in current knowledge to facilitate the improved and more efficient design of future buildings.■


| STRUCTURE magazine
2020.07.01 08:10

When a major tornado happens, it is all over the news. And, every year, the average person may recall hearing about a dozen or so tornado events, if that. So it might be startling to know that, on average, the number of tornadoes that touch down each year in the United States, according to www.ustornadoes.com, is more than 1,200.

And then there are hurricanes. While fewer in numbers – approximately seven hurricanes strike the U.S. every four years, according to the National Oceanic and Atmospheric Administration (NOAA), and while limited in terms of areas effected, hurricanes are often devastating in terms of loss of life and property and typically last for days instead of minutes. Tornadoes are more likely to cause death due to the lack of warning and the inability of buildings to resist wind forces. The building codes do not mandate that all structures be designed for tornadic wind pressures, only those designated as shelters or safe rooms.

Some states, such as Alabama, now require all new schools and state college buildings to have tornado shelters attached or included within the building. In the case of elementary, middle, and high schools, this mandate is financially burdensome as construction budgets are tight. Roof systems in these buildings are typically framed with bar joists and metal deck or cold-formed steel trusses. Changing construction methods for the shelter increases costs. It is financially beneficial to stay with steel.

AISC’s new Design Guide 35, Design of Steel-Framed Storm Shelters, summarizes up-to-date design requirements and guidance to incorporate storm shelters or safe rooms using typical industry-standard structural steel products and materials. The design guide presents a discussion regarding storm shelter design for both tornado and hurricane-force winds. Previous roof decking missile impact tests performed at Clemson University considered the performance of the screw attached to bare deck alone. The bare deck was required to absorb all of the energy created by the missile impact. This was not an economical material or installation solution. This article focuses on a steel industry effort to develop an improved solution for protection from missile impacts resulting from tornados.

Order of Magnitude

The primary difference in a building’s structural system when designed for use as a storm shelter or safe room, as compared to conventional construction, is the magnitude of the design wind forces and the need to withdraw impacts of windborne debris. Safe rooms and storm shelters are designed to resist higher intensity wind speeds, which correspond to higher wind pressures than buildings designed for typical occupancies, including essential facilities, as well as windborne “missiles.” (Note that it is important to understand that these two criteria are not concurrently occurring design events.)

ICC 500, Standard for the Design and Construction of Storm Shelters, and FEMA P-361, Safe Rooms for Tornadoes and Hurricanes: Guidance for Community and Residential Safe Rooms, employ the same criteria for wind speed determination and windborne debris criteria. However, FEMA opts to use the term “safe room” because the design guidance is intended to provide “near-absolute protection” from extreme wind events.

Figure 1. Restroom St. Louis International Airport.

Figure 1. Restroom St. Louis International Airport.

A storm shelter will typically be either an interior room within a building (Figure 1) or a designated wing of a building. However, the concepts presented in Design Guide 35 may also be employed for standalone structures or retrofitting of existing structures. While both ICC and FEMA address both community and residential shelters, Design Guide 35 focuses on community shelters.

Test Protocol

Design Guide 35 summarizes existing test standards. All shelter envelope components must be designed for the impact of windborne debris as evaluated by the debris impact test of ASTM E1886, Standard Test Method for the Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials. ASTM E1886 defines the test apparatus and test missile, whereas ICC 500 defines the pass/fail criteria.

For tornado shelter design, the test missile is nominally 15 pounds. The test missile can be any common softwood lumber species, as defined by the American Softwood Lumber Standard, PS 20. The lumber must be grade stamped No. 2 or better and be free of splits, checks, wanes, or other significant defects. Also, the bow or warp of the missile must be such that stretching a string or wire on the board from end to end is within 0.5 inches of the 2×4’s surface over its entire length. Both defects and bow may affect the performance of the missile, resulting in the missile absorbing some of the impact, thereby reducing the force applied to the test specimen.

Roof and wall surfaces are delineated based on their inclination from horizontal. Vertical surfaces of the shelter envelope, i.e., walls, are defined as surfaces inclined more than 30° from the horizontal. In contrast, surfaces inclined less than 30° from the horizontal, i.e., roofs, are treated as horizontal surfaces.

A tornado test missile is assumed to impact the test specimen at a designated speed, as summarized by Table 1.

Table 1. Speeds for tornado shelter missile.

Table 1. Speeds for tornado shelter missile.

ICC 500 Chapter 8 defines the impact locations for wall, roof, and openings, i.e., doors and windows. The impact locations vary with the test assembly configuration, as illustrated in Figure 2.

Figure 2. Typical Test Specimens (Excerpted from the ICC 500: ICC/NSSA Standard for the Design and Construction of Storm Shelters: Copyright 2014. Washington, D.C.: International Code Council. Reproduced with permission. All rights reserved. www.ICCSAFE.org.)

Figure 2. Typical Test Specimens (Excerpted from the ICC 500: ICC/NSSA Standard for the Design and Construction of Storm Shelters: Copyright 2014. Washington, D.C.: International Code Council. Reproduced with permission. All rights reserved. www.ICCSAFE.org.)

For any roof or wall construction, no more than three impacts are to be made on any one test specimen. Where more than three impacts are required, multiple identical test specimens are to be used. ICC 500 defines the pass/fail criteria as follows:

  • Any perforation of the interior surface of the tested component of the shelter envelope by the missile constitutes failure.
  • Specimens or load-bearing fasteners shall not become disengaged or dislodged during the test so as to endanger occupants. The pass criterion is defined as specimens or fasteners failing to penetrate a witness screen comprised of #70 unbleached kraft paper located within five inches of the interior surface of the test specimen.
  • The permanent deformation of an interior surface of the test specimen shall not exceed three inches.
  • Excessive spalling shall not occur, if applicable.

Industry Impact Tests

The goal of a 2016 industry-supported missile impact test program was to assess the performance of more cost-effective assemblies than had been previously tested. The 2016 tests were performed at Texas Tech’s National Wind Institute Debris Impact Facility and utilized common steel construction methods and materials (Figure 3):

Figure 3. Typical test specimen. Courtesy of Ken Charles and Texas Tech.

Figure 3. Typical test specimen. Courtesy of Ken Charles and Texas Tech.

  • 18 and 20 gage, 1.5-inch-wide rib steel metal deck (commonly referred to as Type B deck)
  • 12K5 open web steel joists
  • HSS 6×3×1⁄8
  • Nail base insulation consisting of 3-inch polyisocyanurate with 1-inch spacers and 5⁄8-inch CDX plywood.

Five test series were performed:

  • Series 1 – 20 gage decking supported on open web steel joists
  • Series 2 – 18 gage decking supported on open web steel joists
  • Series 3 – 18 gage decking supported on HSS
  • Series 4 – 18 gage decking supported on open web steel joists
  • Series 5 – 18 gage decking supported on HSS

Series 1, 2, and 3 were exploratory tests. The test missile penetrated the Series 1, 20 gage decking; thus, subsequent testing focused on the 18 gage decking. Series 4 and 5 were duplicate tests to verify the performance for the 18 gage decking.

Design Guide 35 summarized the research recommendations. Based on the test performance, Series 4 and 5 were deemed to be adequate for horizontal (roof assemblies with a slope of 30° or less) applications for design wind velocities of 250 mph. Series 4 assembly was deemed acceptable for vertical (wall or roof assemblies having a slope over 30°) applications for design velocities of 250 mph. Series 5 assembly was also deemed acceptable for vertical applications if a minimum 5⁄8-inch-thick gypsum board was employed as an interior finish. A screw dislodged during the test, but the kraft paper was not in place during the tests. The researchers judged that the gypsum board would be adequate to capture the screw that dislodged. Typically, the gypsum board would be required to achieve the building code required membrane fire protection.

Design Guide 35 addresses the most current requirements and considerations for storm shelter and safe room design. It should prove to be an invaluable resource and push your next shelter design project to be as safe and cost-effective as possible. The design guide provides the design engineer with alternative economic systems for inclusion in a tornado shelter design. For those projects that employ steel bar joists, metal deck, and an insulated nail base, it allows a tested assembly to be incorporated into the overall building design. Schools utilizing masonry walls, steel bar joists, and metal roof decks can be designed with the same materials throughout. Changes in the area of the building designated as a tornado shelter consist of using the same tradesmen to increase the robustness of the construction. This is accomplished through the closer spacing of bar joists, the use of slightly heavier metal deck, and thicker masonry walls with more grout and reinforcing steel. This approach compares favorably with the use of alternative construction, which may require additional subcontractors and tradespeople.

Steel has the properties conducive to the utilization of steel-based roof and wall assemblies to achieve economical shelter design. Engineers have always been able to design these structures for strength, supporting their designs with calculations for bending stresses, shear, and pullout and pullover of fasteners. The missing link, so to speak, was the reaction of the assemblies to missile impact. With the recent testing for missile impact that utilized the entire roof and wall assembly to absorb the energy, economical steel-based shelter design can be technically justified. AISC and its industry partners have given the design engineer the tools needed in the form of Design Guide 35. The guide is available at www.aisc.org/dg, where you can also access AISC’s entire library of Design Guides.■


| STRUCTURE magazine
2020.07.01 08:10

Is the Wind Blowing in the Right Direction?

The ASCE 7-16, Minimum Design Loads for Buildings and Other Structures, has been published in accordance with the International Building Code (IBC 2018), incorporating updates regarding wind load calculations from ASCE 7-10. This article relates to wind uplift on flat and gable roofs of major logistic centers with slopes ≤ 7 degrees and buildings ≤60 feet in height. The article focuses on the wind uplift loads on the roof elements of joists and girders. For joist wind uplift loads, the method of Components and Cladding in Chapter 30 of ASCE 7 is adopted. For girders, considering the effective wind area is larger than 700 square feet for typical major logistic centers, the Main Wind Force Resisting System (MWFRS) method in Chapter 27 is adopted.

The wind load updates can affect the design of roof joist and girder elements. The sizes and bracing required can be reduced if the wind uplift loads are smaller.  The updates are examined by selecting multiple cities in the U.S. and comparing the results. A case study in the city of North Las Vegas is also presented to show the influence on the design of roof joists and girders.

Basic Wind Speed Comparisons

In ASCE 7-16, the basic wind speeds are updated for risk category II buildings, and many cities see a significant reduction. Figure 1 summarizes the differences for risk category II buildings in major U.S. cities. The values are derived directly from the maps, and special wind zones are not considered. For Houston, Miami, New Orleans, and New York City, the basic wind speeds remain the same. For the remaining major U.S. cities, the basic wind speeds are decreased by 1.7% to 11.8%.

Roof External Uplift Pressure Coefficients

The roof External Pressure Coefficient (GCp) comparison in this article is only limited to ASCE 7-16 Figure 30.3-2A, which is updated from ASCE 7-10 Figure 30.4-2A, for components and cladding of buildings with height less than 60 feet and gable roofs with θ ≤ 7 degrees.

Figure 1. Basic wind speed (mph).

Figure 1. Basic wind speed (mph).

Figure 2. External pressure coefficient comparison for center zone

Figure 2. External pressure coefficient comparison for center zone.

The first significant change is the zone divisions. Another major change is the external pressure coefficients with respect to the effective wind areas. Figure 2 shows the comparison of external coefficient values between ASCE 7-16 and ASCE 7-10 at the center zone. In Figure 2, if the effective area is 500 square feet, the value can be reduced by 40% and, when the area becomes more, the reduction can be up to 60%.

Joist Framing Wind Uplift and Pressure Comparisons

The method used to calculate wind uplift and downward pressure for the design of joist framing is adopted from ASCE 7-16 and 7-10 Chapter 30, Wind Loads: Components and Cladding. The comparison is based on an effective wind area of 400 square feet. For ASCE 7-10, the building type selected is Building Enclosed. For ASCE 7-16, two building types are considered, Building Enclosed and Building Partially Enclosed.

Figure 3. Roof joist wind uplift pressure ratio.

Figure 3. Roof joist wind uplift pressure ratio.

Figure 3 shows the roof joist wind uplift pressure ratio between ASCE 7-16 Enclosed Building and 7-10 Enclosed Building. Note in Figure 3 that all the cities see a significant decrease of 10% to 40% due to the reduction of external pressure coefficients.

Figure 4. Roof joist wind uplift pressure ratio.

Figure 4. Roof joist wind uplift pressure ratio.

Figure 4 shows the roof joist wind uplift pressure ratio between ASCE 7-16 Partially Enclosed Building and 7-10 Enclosed Building.  Due to the higher internal pressure coefficient, Charleston, Houston, Miami, New Orleans, New York City, and Philadelphia see an increase from 5% to 27%. However, Atlanta, Boston, Chicago, Columbus, Dallas, Denver, Las Vegas, Los Angeles, Memphis, Phoenix, Portland, San Antonio, and Seattle still see up to 15% reduction.

Why compare ASCE 7-16 partially enclosed to ASCE 7-10 enclosed? For many buildings, structural engineers consider “enclosed” as the default. However, “partially enclosed” can give more flexibility when considering future uses of a building. A minimal increase in the pressure ratio between enclosed and partially enclosed may provide additional options by using ASCE 7-16 partially enclosed.

Girder Framing Wind Uplift Comparisons

Per ASCE 7-16 and ASCE 7-10 30.2.3, component and cladding elements with a tributary area greater than 700 square feet shall be permitted to be designed using MWFRS provisions. Assuming the roof girders have a tributary area larger than 700 square feet, which is very common for industrial buildings, the roof uplift pressure calculation can be based on Chapter 27, Wind Loads on Buildings-MWFRS.

Figure 5. Roof girder wind uplift pressure ratio.

Figure 5. Roof girder wind uplift pressure ratio.

Figure 5 shows the roof girder wind uplift pressure ratio between ASCE 7-16 Enclosed Building and 7-10 Enclosed Building. From Figure 5, note that Houston, Miami, New Orleans, and New York City have the same value, whereas all the rest of the cities see a decrease of 5% to 15%.

Figure 6. Roof girder wind uplift pressure ratio.

Figure 6. Roof girder wind uplift pressure ratio.

Figure 6 shows the roof girder wind uplift pressure ratio between ASCE 7-16 Partially Enclosed Building and 7-10 Enclosed Building.  It can be concluded that due to the higher internal pressure coefficient, all the cities see an increase.

Case Study

A case study in the city of North Las Vegas demonstrates the comparison of wind uplift pressure for roof elements, including joists and joist girders. The results shown are wind-net-uplift pressures using a load combination equal to 0.6D-0.6W. The dead load is taken as 8.5 psf for a joist and 10.5 psf for a joist girder considering roofing, plywood, rafters, sprinklers, and member self-weight. No miscellaneous loads are considered.

Figure 7. Joist net uplift – ASCE 7-16 enclosed building. Joist net uplift – ASCE 7-10 enclosed building.

Figure 7. Joist net uplift – ASCE 7-16 enclosed building. Joist net uplift – ASCE 7-10 enclosed building.

Figures 7, 8, 9, and 10, show four different comparisons of roof element wind net uplift. They are joists under ASCE 7-16 Enclosed Building vs. 7-10 Enclosed Building, joists under ASCE 7-16 Partially Enclosed Building vs. 7-10 Enclosed Building, joist girders under ASCE 7-16 Enclosed Building vs. 7-10 Enclosed Building, and joist girders under ASCE 7-16 Partially Enclosed Building vs. 7-10 Enclosed Building. The values of the case study reflect the analysis presented above.

Figure 8. Joist net uplift – ASCE 7-16 partially enclosed building. Joist net uplift – ASCE 7-10 enclosed building.

Figure 8. Joist net uplift – ASCE 7-16 partially enclosed building. Joist net uplift – ASCE 7-10 enclosed building.

For the center zone, the joists see a reduction for both comparisons. There is a significant reduction for girder joists when comparing ASCE 7-16 Enclosed Building and 7-10 Enclosed Building and slight increase between ASCE 7-16 Partially Enclosed Building and 7-10 Enclosed Building.

Figure 9. Joist girder net uplift – ASCE 7-16 enclosed building. Joist girder net uplift – ASCE 7-10 enclosed building.

Figure 9. Joist girder net uplift – ASCE 7-16 enclosed building. Joist girder net uplift – ASCE 7-10 enclosed building.

The reduction of net wind uplift on roofs could reduce the joist and joist girder cost by cutting down the bottom chord size and joist brace spacing. For the case study project in the city of North Las Vegas, comparing ASCE 7-16 Enclosed Building type with 7-10 Enclosed Building type, the roof joist net-uplift in the major center area is reduced from -14.4 psf to -6.2 psf. The bottom chord of the joists will see significantly less compression forces. The joist bottom chord size can be reduced from LL 2 x 0.203 to LL 2 x 0.145, and joist brace spacing can be relaxed to 12 feet from 10 feet. The reduction in the brace quantity will reduce the cost for the braces from the manufacturer and the install cost due to fewer braces.

Figure 10. Joist girder net uplift – ASCE 7-16 partially enclosed building. Joist girder net uplift ASCE 7-10 enclosed building.

Figure 10. Joist girder net uplift – ASCE 7-16 partially enclosed building. Joist girder net uplift ASCE 7-10 enclosed building.

The steel takeoff and cost reduction will depend on project location, the nature of the project, and contractors. The numbers above are the estimated impacts for the case study project, applicable in this article only.

Conclusion

As noted earlier, ASCE 7-16 basic wind speeds are updated for risk category II buildings. Wind speeds have remained the same or have been lowered for the major U.S. cities studied in this article.

It is also noted that, within the center area of the roof, the external uplift pressure coefficients from ASCE 7-16 are reduced significantly, by up to 60%, for the major center zone, as shown in Figure 2. The reduction of the external uplift pressure coefficient, combined with a reduction in basic wind speed, yields a significant reduction in roof wind uplift for many U.S. major cities. Results of the roof net uplift case study in the city of North Las Vegas illustrate the potential for significant savings from wind load reductions for both joists and joist girders and, as a result, lower overall construction material cost.■


| STRUCTURE magazine
2020.07.01 07:50

Business Practice Tips for the Structural Engineer

Long before Cheryl’s “she-shed” was struck by lightning… my shed was destroyed by a rotted oak tree blown over during Hurricane Irene. My home and office were without power for several days. All the while, calls were coming in from clients to evaluate the damage to their buildings. Although I had been engineering structures in flood zones for many years by then, when you are personally and professionally affected by storm damage, it makes a lasting impact.

Most structural engineers will, at some point, take on a project that involves designing a building located in a flood zone. Such projects require an understanding of the technical engineering issues involved with the site topography, geology, sources of flooding, and how wind and water will affect the proposed building structures and foundations. Beyond that, structural engineers need to understand the business practice issues associated with such projects, including client evaluation, assessing the risk/reward curve, and knowing when to ask for help or pull the plug. Moreover, an emergency management plan for your firm is time well spent to make sure your clients are taken care of following a disaster, and your business can operate.

Hurricane Irene barrels towards coastal buildings in Fairfield, CT, August 2011.

Hurricane Irene barrels towards coastal buildings in Fairfield, CT, August 2011.

  • Pull up a flood map for every project. Flood prone areas for a community are delineated on a series of Flood Insurance Rate Maps (FIRMs) published by FEMA. The current FIRM for a given property can be accessed on FEMA’s Map Service Center website, free of charge, either using the street address or latitude/longitude (https://msc.fema.gov/portal/home). It is easy to print an 8½ x 11 excerpt of the flood map showing the property you are interested in – called a “FIRMette.” The printout is free and only takes a few minutes once you have the property location. The FIRMette is also a rough double-check that the civil engineer is showing any flood boundaries and flood elevations accurately on the site plan. If there is a discrepancy, ask.
  • Are you practicing in your area of competence? If you have never designed a foundation subject to scour or had to calculate wave forces, are you comfortable going it alone? What about a submerged basement design; what should the design water table be based on, flooding or groundwater? The project’s geotechnical engineer can provide crucial guidance on erodibility, liquefaction potential, and soil permeability and its effect on the design water table for a flood event. Do your foundations constitute an impermissible obstruction in a V zone? (“V” stands for velocity. V zones are Coastal High Hazard Areas – essentially, they are areas of high energy flooding with wave action.) A coastal engineer expert in modeling storm events, wave runup, scour depth, and calculation of pressures may also be a team member you will want. Speak up about what you are knowledgeable about and what areas of the project warrant additional consultants.
  • Do not over-promise. As with earthquakes, you are designing to minimum code requirements for structural integrity and life-safety. That does not mean a structure will not sustain damage. Some damage is all but guaranteed. For instance, a building supported on deep foundations will still be standing after a flood scours the soils from underneath it, but then the crater left behind will need to be filled in. Breakaway walls and slabs on grade will breakaway and need to be replaced. There will be a loss of landscaping and hardscaping. Roofing and siding materials may be blown off the building. Water and moisture can damage finishes. And, incoming utilities may be severed. Flood insurance will cover some but not all damage. Be sure to temper the Owner’s expectations with a dose of reality.
  • When the client insists on having a basement . . . even when it is a really bad idea. When a basement is permitted in a flood zone, do not count on pumping to avoid designing for hydrostatic pressure and buoyancy. Pumps will eventually fail, as can backup power sources. Although basements in limited circumstances are permitted in flood zones, they are expensive, risky, and usually a bad idea. When the flood regulations allow a basement, and the project must have one, NEVER count on sump pumps to depress the water table and keep the basement dry. DO design the basement as an “inverted bathtub” (like a bathtub but with the water on the outside) for the full effects of hydrostatic pressure and buoyancy. This will mean using a mat slab foundation for the basement floor instead of a thin slab on grade. ALWAYS have a fail-safe in case water levels are higher than anticipated. For low-rise light-frame buildings, the building and foundation together will not weigh enough to resist buoyancy. Thickening concrete to add mass is usually counterproductive. Anchor the foundation walls and mat slab into the ground using rock or soil anchors. Or, provide hydrostatic relief through openings in the slab with raised rims that will allow floodwaters to overtop the rim to relieve pressure once the maximum design water table height is exceeded. The last thing you want is for the foundation to heave and fail from hydrostatic pressure, because such a catastrophe may prove fatal for the building – and your livelihood. When you explain to the client all the weak links involved in submerging a basement, the proposed basement will go away – if you are lucky.
  • Higher is better – if you can. An owner and their designer can choose to elevate a building higher than necessary. Often, in coastal communities, the design team is simultaneously working to fit in the maximum number of stories possible under the zoning height limit, so you may not get much higher than the minimum. That also means you will be pressed to minimize structural depth to fit everything in.
  • Know the FEMA Technical Bulletins. Although not law, FEMA publishes a series of Technical Bulletins to explain various common design and construction issues for buildings in flood zones. The bulletins are written by FEMA’s staff and consultants and are important guidance on how to interpret and implement FEMA’s model regulations adopted by local jurisdictions. Perhaps more importantly, the Technical Bulletins are a window into how the jurisdiction, and FEMA itself, will judge your design.
  • “Yes, but so-and-so said we could do it,” doesn’t take you off the hook. Have you received a schematic design from an architect that shows something non-compliant? Like a solid foundation in a V zone? An addition that is set below the BFE to match the existing building? (BFE = Base Flood Elevation, which is typically found on the FIRM). Are you told that deep foundations are not required when you know your building sits on erodible beach sand? Raise the issue. Most communities that participate in the National Flood Insurance Program (NFIP) are on top of their game and are the gatekeepers preventing non-compliant buildings from getting built by owners inclined to push the limits. Maybe the community is a small town with part-time zoning and building staff not in tune with flood-resistant design. If you are told “shut up and stamp it” – do not do it. FEMA takes violations of the NFIP very seriously, and they do not hesitate to bring enforcement actions against participating communities. If your Owner has to retrofit their new building to appease FEMA (or their flood insurance provider), that Owner may come looking for a pocket to reach into; avoid letting it be your pocket.
  • Non-residential projects have more leeway. There are a few reasons for this. Commercial or institutional projects typically engage a full design team, with a project architect, structural engineer, and other consultants. Single-family and townhome-style residential projects may not have a structural engineer or even an architect. That is one reason, for example, why a basement below the BFE is not permitted for a residential project but is permitted for a mixed-use or non-residential project. Another factor is the risk associated with the building’s use. If an office building or store is flooded, people cannot shop or go to work; if residences are flooded, people may be displaced from their homes.
  • What about your business? If you practice in a region of the country subject to flooding, it is not just your projects you have to worry about. Is your office located in a flood zone? How about your employees’ homes? When a disaster strikes, can they get to work? Will you be able to respond to your clients? Power may be out for some time; does your office need backup power? Are your files kept in a basement? Being prepared for a flood could be crucial to your business’ survival. Plan ahead.
  • When in doubt, take a pass. There is no harm in declining a project that is a no-win situation. The same criteria you use to select clients can be applied to projects in flood zones. Has the existing building been damaged before? Will the proposed project make conditions better or worse? Are you building on an erodible site? Does the client insist on spread footings instead of piles, when you know the soils are prone to scour? If you know the design will not comply with the flood regulations – walk away. It is not worth the risk. Some of your best projects may be the ones you never take in the first place.■

| MMK
2020.06.30 07:57
A Magyar Mérnöki Kamara elnökének közleménye a gázszerelői nyilvántartással összefüggően fizetendő eljárási díjról  

This exercise will further develop the parametric tower model by creating a panelized system for the tower’s curved facade.


 DAYTON, Ohio (June 29, 2020)  Demand for walkable urban places coupled with the growing number of pedestrians has vehicle bridge owners looking for ways to add sidewalks to provide safe places for people to walk and ride.  The weight and cost associated with traditional concrete is typically prohibitive and time to cure disruptive. The new requirement for social distancing is boosting demand for sidewalks up to 15 ft. wide. Composite Advantage’s lightweight FiberSPAN-C fiber reinforced polymer (FRP) cantilever sidewalk products are COVID-19 compliant.

The cost-effective FRP panels are 80 percent lighter than reinforced concrete panels. Because the cantilevered sidewalk is prefabricated, construction is quicker and installation costs lower. FRP composite material’s corrosion resistance to chemicals and water means zero maintenance for a structure that will last nearly 100 years.  “Cantilever sidewalk designs depend on a number of functional and load requirements,” says Scott Reeve, marketing director for Composite Advantage, now part of the Creative Composites Group. “One has to consider daily traffic volumes, whether or not the sidewalk will have to accommodate both pedestrians and cyclists and whether or not the sidewalk will be used to view special events.”

Design flexibility allows FRP sidewalks to be engineered and installed on both sides of a bridge to accommodate the ebb and flow of commuters, recreationists and bicyclists. FRP is able to support a pedestrian live load of 90 pounds per square feet. For sidewalks that are seven ft. to 10 ft. wide, FRP panels are designed to support a maintenance vehicle weighing 10,000 lbs. FRP sidewalks wider than 10 ft. can accommodate an ambulance weighing 20,000 lbs. Different railing styles are available with heights ranging from 42 in. to 54 in.  CA uses a commercial polymer aggregate system to provide a non-slip surface overlay. Color options are available to provide aesthetics or direct traffic flow

Composite Advantage supplies innovative fiber reinforced polymer (FRP) products for major infrastructure markets. To create its engineered solutions, CA pairs progressive designs with its capability to mold large parts, perform on-site assembly, and support customer installations.  The supplier has been developing lightweight, high-strength, cost-effective FRP goods for structurally demanding applications and corrosive environments since 2005. Many of these products have paved the way for first-time use of FRP composites in infrastructure, rail and water applications because of their performance attributes.  The supplier’s comprehensive lineup includes bridge decks, trail bridges, cantilever sidewalks and rail platforms to fender protection systems, pilings, naval ship separators and other waterfront structures. CA is member of the Creative Composites Group, a subsidiary of Hill and Smith Holdings PLC.

Visit www.compositeadvantage.com or contact Composite Advantage at 937-723-9031 or info@compositeadvantage.com.

The post Light Weight, Design Flexibility Make FRP Cantilever Sidewalks COVID-19 Compliant appeared first on Civil + Structural Engineer magazine.


| Tervlap
2020.06.30 09:04

Kép

Magyarország célja, hogy 2030-ra jelentős innovátorrá váljon, amihez növelni kell az állami kutatás-fejlesztési (K+F) ráfordításokat, ezért döntöttek arról, hogy folyamatosan emelik a támogatásokat. A következő uniós keret költségvetési időszakában kutatási programokra több mint 80 milliárd euró áll rendelkezésre, amiben a magyar kutatóegyetemeknek fokozottabban részt kell venniük. Palkovics László innovációs és...

| Tervlap
2020.06.30 12:50

Kép

Miközben világszerte már nemcsak a múlt század közepén épült brutalista alkotásokat, hanem az azt követő évtizedek posztmodern, sőt, high-tech épületeit is sorra műemléki védelem alá vonják, hogy minden kor jelentős műveit megőrizzék az utókornak, Magyarországon mindezek az értékek az üldözni való kategóriába tartoznak. Ha ez így megy tovább, néhány éven...

| Tervlap
2020.06.29 07:44

Kép

A Zengő a Mecsek legmagasabb csúcsa, Pécstől északkeleti irányban, a Kelet-Mecsek legkevésbé bolygatott tájain fekszik, magassága 682 méter. Alkotó kőzetei a permi homokkő, a jura- és triászkori mészkő. A hegyhez népmondák, legendák, népszokások sora kötődik. Nevét a népmonda azzal magyarázza, hogy a hegy zúgását a belsejében rekedt kincskeresők kiabálása okozza,...

| Tervlap
2020.06.29 05:33

Kép

Radványi György 1949. augusztus 4-én született Ózdon, 1973-ban szerzett építészmérnöki diplomát, 1986-tól vezető tervező volt, 2011-ben főépítészi vizsgát tett. A Műegyetem címzetes egyetemi tanáraként, illetve Sátoraljaújhely és Füzér főépítészeként is dolgozott. Alkotói életműve Sátoraljaújhely és Széphalom általa tervezett épületeiben teljesedik ki, melyek közül kiemelkedik a Kazinczy-emlékhely kertjében megépült Magyar Nyelv...

Kép

A legrosszabb megoldást sikerült megtalálni a Teherelosztóról szóló vitában: sosem volt, régies kulisszahomlokzatot kaphat az épület.

| MMK
2020.06.29 11:18
Az Épületgépészeti Tagozat és a Vízgazdálkodási- és Vízépítési Tagozat kezdeményezésére közzétesszük a Magyar Víziközmű Szövetség nyilatkozatát, amely egyértelműen leszögezi, hogy a Magyarországon szolgáltatott ivóvíz kiválóan megfelel az Európai Uniós előírásoknak és jogszabályoknak, minőségét tekintve pedig kiemelendő, hogy hazánkban a csapvíz az egyik legszigorúbban ellenőrzött élelmiszer.

| AEC Magazine
2020.06.29 11:18

Image User requested platform features designed to boost collaboration and communications across the construction project lifecycle

Read More ...


Kép

A független polgármester szerint Szentendréhez hasonlóan ők sem tudják lehívni az évekkel ezelőtt megítélt támogatást, amiből meg lehetne menteni a két épületet.

| Tervlap
2020.06.28 06:53

Kép

A görög Kapsimalis Architects által tervezett Saint Hotel az Oia falu peremén lévő épületek között, egy tenger fölé emelkedő sziklán található.  A meredek domboldalon elhelyezkedő épület szobáit földbe ásták, ezzel tudtak akadálytalan kilátást biztosítani a sziget vulkáni öblére a lépcsőzetesen egymás fölé helyezett lakrészekből. Mind a tizenhat szoba önálló teraszra...

| DebunkTheBIM
2020.06.28 06:16
Welcome to my Blog. 

Truth to be told, it has been my wife’s blog for over 10 years, but she does not mind sharing her established platform with me.


She knows a lot about BIM, I call her a BIMfluencer.


If there is such a thing, like, forever wanting to change the world preaching about BIM.


I’m a scientist. I like things with no frills, going straight to the meaning of the lesson.

My message today is simple, though might not be as short and snappy as I’d like it to be:


If you work in construction, you can’t ignore BIM – yet I can bet on that, you are not sure what good is it to you. (even if your company is ‘BIM enabled’)

If you work in construction, you are likely to waste a lot of time/money because how projects are documented.


BIM, drawings and specs are hurting you and we’re here to help.

Our BIM company is like no other!

Our services are designed to verify, filter, sort and serve up information in the most efficient way for our clients.

SHORTCUT is the key word!


Here is an example. Entire house documentation packaged in one model including drawings and specifications. And all cross referenced, accessible even on your mobile apps.





Get in touch through LinkedIn or Facebook if you’d like to know more!



In Grasshopper, DataTrees are used to organize data in more complex structures than a single ordered List. An easy way to think of…


| Tervlap
2020.06.26 07:55

Kép

A vágy az elismerésre ősidők óta ösztönös az emberben. Ez sarkall még nagyobb és jobb teljesítményre, arra, hogy kitűnjünk a tömegből. Nem mindegy azonban, hogy az értékteremtő munkát milyen elismerés illeti meg: egy díj rangja és hitelessége annál nagyobb, minél jobban meg tudja őrizni függetlenségét és valóban csak a teljesítményre...

| Tervlap
2020.06.26 07:32

Kép

A pályázóknak az alábbiakat kell benyújtaniuk: a létesítmény bemutató anyagát digitális formátumban, mely tartalmazza az épület főbb jellemzőit (alaprajzait, metszeteit és homlokzatait) és rövid építészeti műleírást legfeljebb egy A4 oldal terjedelemben, legalább 5 db digitális fotót a megvalósult épületről, 300 dpi felbontásban, a szerző nyilatkozatát arról, hogy a mű saját...

At the heart of any Grasshopper definition is data — components process and create data, while wires transport the data between components.


| MMK
2020.06.26 03:15
Megjelentek az épületgépész társadalom legnagyobb rendezvényéhez, az Országos Magyar Épületgépész Napok 2020 rendezvényeihez kapcsolódó pályázati felhívások: az Év embere díjakra való felhívás és a Tervezői pályázat kiírása.

NYU Tandon School of Engineering, T.Y. Lin International, and Sam Schwartz Engineering release conceptual designs for a pedestrian-bicycle bridge from Queens to Manhattan. Two other bridges, from Brooklyn and New Jersey, are in early planning stages.

BROOKLYN, New York, Wednesday, June 24, 2020 – The “Queens Ribbon,” a concept design for the first new bridge to Manhattan’s central business district in over a century, was unveiled today by a consortium of the NYU Tandon School of Engineering, T.Y. Lin International, and Sam Schwartz Engineering. The pedestrian-bicycle bridge would connect Queens to Manhattan.

The consortium was formed in the wake of Covid-19 to develop transportation improvements that would not only be of value during “normal” times, but would also provide a lifeline in future crises. During the Covid-19 outbreak, New Yorkers have been turning to walking and biking in great numbers. After 9/11, Super Storm Sandy, the 2003 blackout, and transit strikes, walking and biking became the best, and in some cases, the only alternative for many travelers to and from Manhattan’s Central Business District (CBD).

Even before the coronavirus outbreak, cycling over the East River bridges soared  by 132% over the last decade, yet bikers and pedestrians have been squeezed into tight spaces that  inhibited growth and compromised safety for both groups. As New York City proceeds with plans to add hundreds of miles of protected bike lanes on its streets, the demand for causeways allowing cyclists and walkers to cross rivers will only increase. The new bridge will provide safe and separate areas for its users to commute and stroll, and will be an iconic visual addition to the East Side of Manhattan, Long Island City, and to the surrounding areas in Queens.

The 20-foot-wide bridge will have an observation belvedere providing spectacular, panoramic views, and will be a draw for New Yorkers and tourists alike. It will have elevator access to Roosevelt Island, and its network of cycling and pedestrian paths, and the Cornell Tech campus.

“The Queens Ribbon will offer tremendous value in so many ways – from an environmental perspective, an aesthetic perspective, and a health perspective,” said Dr. Michael Horodniceanu, PE, Professor and Chair of NYU Tandon’s Institute of Design & Construction (IDC) Innovation Hub. “The IDC Innovation Hub is proud to have participated in the development of the bridge thus far, and we look forward to continuing our association with T.Y. Lin International and Sam Schwartz Engineering in seeing this and future ‘sister’ bridges through to fruition.”

The bridge is an exemplar for how NYC can grow sustainably, drawing New Yorkers and tourists to spectacular views from the bridge. At a preliminary cost estimate of $100 million, the Queens Ribbon will be a small investment to make when compared to the savings that will be derived from reduced pollution and traffic.

“The Queens Ribbon will become an essential element of the region’s transportation network expanding opportunities for safe and accessible travel to Manhattan for bicyclists and pedestrians,” said Gerard Soffian, PE, RSP1, an adjunct professor at NYU Tandon, and former director of the NYC Department of Transportation’s bicycle program.

“The urban travel mode of the future won’t be flying cars, or robo-cars or even cars.  It will be shoes and bikes,” said Sam Schwartz, Founder and CEO of Sam Schwartz Engineering. “Cities can best thrive on these low impact, non-polluting, equitable, and healthy forms of transportation.”

“The Queens Ribbon will be more than a connection, it will also be a destination. T.Y. Lin International has developed an innovative and cost-effective bridge concept — a pedestrian bridge of exceptional lightness and beauty that is floating in the air and yet has an immense presence,” said Dr. Sajid Abbas, PE, a Senior Vice President at T.Y. Lin International.

The team is also in the early planning stages for two additional bicycle-pedestrian bridges into Lower Manhattan. One from New Jersey in the Hoboken/Jersey City area would be the first carbon-free transportation route from the Garden State into Manhattan’s Central Business District, and the second crossing from Brooklyn would relieve the current unsafe space constraints on the Brooklyn Bridge’s bikeway/walkway.

Dr. Michael Horodniceanu of the NYU Tandon School of Engineering and Bala Sivakumar, a Vice President with T.Y. Lin International, unveiled plans for the Queens Ribbon 11 a.m. today at the planned Midtown terminus of the bridge at East 51st Street and Beekman Place.

Visit HERE for the project’s report, more images, and information about the team.

Media Contacts

Josh Rogers                                                   Judy Cooper

646.734.6146 (cell)                                          646.997.3607 (office)

646.801.3932 (office)                                       917-331-2590 (cell)

jrogers@samschwartz.com                               judy.cooper@nyu.edu

 

 

About the New York University Tandon School of Engineering

The NYU Tandon School of Engineering dates to 1854, the founding date for both the New York University School of Civil Engineering and Architecture and the Brooklyn Collegiate and Polytechnic Institute (widely known as Brooklyn Poly). A January 2014 merger created a comprehensive school of education and research in engineering and applied sciences, rooted in a tradition of invention and entrepreneurship and dedicated to furthering technology in service to society. In addition to its main location in Brooklyn, NYU Tandon collaborates with other schools within NYU, one of the country’s foremost private research universities, and is closely connected to engineering programs at NYU Abu Dhabi and NYU Shanghai. It operates Future Labs focused on start-up businesses in downtown Manhattan and Brooklyn and an award-winning online graduate program. For more information, visit engineering.nyu.edu.

 

T.Y. Lin International

T.Y. Lin International is a global, multi-disciplinary engineering services firm recognized for solving some of the most significant infrastructure challenges of our age. Ever mindful that its work has a significant impact on people’s daily lives as well as on the lives of future generations, the firm ensures project success and sustainability by strategically mobilizing the collective power and diverse expertise of its global organization; assembling multi-disciplinary teams; leveraging experience and state-of-the-art technical solutions; and sharing knowledge among regions.

This value-driven approach and unwavering commitment to excellence consistently results in award-winning projects, delivered on schedule and within budget, for satisfied clients. T.Y. Lin proudly continues to stand as one company, driven by one vision.

 

Sam Schwartz Engineering

This industry-leading team specializes in developing context-sensitive transportation solutions for urban mobility in New York, nationally, and globally. It identifies transportation and social impacts and provides creative, multi-modal plans that are grounded in technically rigorous analysis and industry-accepted design standards, working towards larger policy goals such as Vision Zero, economic development, social equity, environmental and climate resiliency, and design excellence. The firm also works to balance the needs and improve the quality-of-life of all users, including those using transit, walking, biking, driving, hailing rides, and moving freight.

The post The ‘Queens Ribbon’ — A new bridge for the Millennium First New Bridge to Manhattan’s Business District Since 1909 appeared first on Civil + Structural Engineer magazine.


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