Generative design and AI are starting to have a huge impact in the AEC industry, improving quality, lowering costs and reducing risk
Autodesk enhances Dynamo for Revit and adds new sample studies to Generative Design for Revit to optimise room layouts
The transition from BIM to VR used to take hours, even days, but now it’s so seamless, VR can truly influence the design process
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Partnership with nPlan to explore new data driven contracting models for major project delivery
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Az elindított beruházások számát nézve, április és június közötti időszakban olyan kevés projekt kivitelezése indulhatott el, amely alacsony számra a felívelés kezdete óta nem volt példa. Budapest és környékének részesedése az előző negyedévben drasztikusan megnövekedett a korábbi évekhez képest a kivitelezési fázisban lépő társasházi lakásépítések összegéből, a január és március...
Az ásatások eredményei nemcsak az épületegyüttes eddig kevéssé ismert korszakairól árulnak el titkokat, de az egykori szerzetesi életről is. A román kori építészet ikonjának számító jáki templomot, az egykori jáki bencés apátság monumentális bazilikáját 1220 körül alapították, és 1256-ban szentelték fel Szent György tiszteletére. Építése során több alkalommal is változtattak...
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Sitescape software designed to lower point of entry for reality capture with point clouds in the AEC sector
Egy volt acélgyár területén mutatják be a Régi Nyári Palota rekonstrukcióját pekingi építészek.
The 2022 edition of the AISC Specification for Structural Steel Buildings (AISC 360) draft will be available for public review from August 3, 2020, until September 14, 2020.
AISC 360 provides requirements for the design, fabrication, and erection of structural steel-framed buildings and buildings with structural steel acting compositely with reinforced concrete. This is the first public review of this draft specification, which is expected to be complete and available in late 2022.
The draft Specification will be available as a free download at aisc.org/publicreview between August 3 and September 14, 2020. Printed copies are also available (for a $35 nominal charge) by calling 312.670.5411.
Please submit comments using the form provided online or to Cynthia J. Duncan, AISC’s director of engineering (firstname.lastname@example.org), by September 14, 2020, for consideration.
A beruházás az EP Konstruktív Kft. közreműködésével készül. A régi könyvtárépületet először 1964-ben újították fel, majd 1980-ban esett át egy újabb korszerűsítésen. A József Attila Megyei és Városi Könyvtár épületének sarokrészén egy úgynevezett tudástorony épült a rekonstrukció során, mely a gazdasági és a kiszolgáló részt takarja. Itt találhatók az irodák,...
Breuer Marcel remekműve egy tekintélyes méretű domboldalon helyezkedik el, a Hudson folyóra néző kilátással. Az Amerikában nagyra becsült magyar származású építész egyik legkiválóbb műve 1953-ban épült Vera Neumann művésznő számára, amelyet aprólékos gonddal és szeretettel állítottak vissza elegáns, modernista pompájában. A modernista villaépület egy kéthektáros telken helyezkedik el, a Hudson...
An automated monitoring system, optical total stations, GNSS receivers and other structural monitoring instrumentation continuously monitors Sri Lanka’s tallest dam — providing a 360-degree view in real-time — of all dam movements.
Victoria Dam is the tallest dam in Sri Lanka, located on the Mahaweli River and about 20 kilometers (12 miles) from the town of Teldeniya. A double-curvature concrete arch dam, it is vital to the area in terms of agricultural irrigation and the production of hydroelectric power. Construction of the dam started in 1978 and was completed in April 1985.
Due to the age of the dam and its importance to the infrastructure of the country, the Mahaweli Authority of Sri Lanka determined the dam’s original monitoring system required a major upgrade. Authorities needed continuous monitoring capabilities to analyze the structural integrity of the dam, as well as to understand its behavior according
to the dam’s original design. The team investigated modern structural monitoring technology and ultimately selected Trimble sensors and Trimble 4D Control software to build a sophisticated motion monitoring instrumentation network.
The crown jewel of Sri Lanka dams
Considered by many as the crown jewel of Mahaweli Development Projects, the Victoria Dam is built in a deep valley just above the Victoria Falls rapids and 300 meters (984 feet) below the point where the
Hulu Ganga river meets the Mahaweli River. At the time of its original construction, the dam’s funding, design, and the technical expertise was provided by the United Kingdom. Then Prime Minister Margaret Thatcher was at the dam’s ceremonial opening in 1985 along with then-president of Sri Lanka, J. R. Jayewardene.
The dam is 520-meters long and 122-meters high (1,706-feet long by 400 feet high) and has a width of six meters (19 feet) at the crest and 25 meters (82 feet) at the base. Water from the dam is fed to a powerhouse via a 5,646 meter (18,523 foot) tunnel. From there, tanks feed three 70 megawatt, 12.5 kV turbines, which produce up to 780 gigawatt hours of electrical energy annually (roughly 6 percent of Sri Lanka’s power). The dam creates the Victoria Reservoir which has a gross storage capacity of 722,000,000 cubic meters. (Source: Amazing Lanka).
The region where the dam is located has periods of extreme rainy seasons, which can dramatically impact reservoir water levels to potentially unsafe tolerances. When the dam was originally constructed, engineers installed a comprehensive monitoring system that included a geodetic system and instruments embedded into the dam’s structure. Monitoring tasks were conducted manually, including the geotechnical sensors that were surveyed by staff every two weeks and the geodetic points, which were measured and recorded on an annual basis.
Original monitoring equipment shows its age
Over the years, some of structure’s original measurement equipment stopped working properly, parts became unserviceable, and the accuracy of the data produced was compromised. Er. S.R.K. Aruppola, Director of Operation and Maintenance for Victoria Dam, explains the dam’s conventional manual geodetic measurement processes were becoming tedious and dangerous to manage as the terrain is steep and slippery. Measuring and recording the dam’s movement with these instruments was also prone to human error, requiring the team to fix each instrument on four different pillars and take multiple sets of readings at separate intervals. Adding concern, minor cracks in the dam were found in 1996.
After consulting with technology specialists, the dam’s director and his team began designing a fully-automated, real-time geodetic system to replace the manual monitoring system. The new monitoring system is comprised of several components, including Trimble NetR9 Ti-M GNSS receivers and GNSS antennas, Trimble S9 robotic total stations, Trimble DiNi digital precise leveling instruments, automated water level reading systems and the integration of other geotechnical instrumentation. In addition to these components, all movement sensors were designed to connect to the core of the monitoring system — Trimble 4D Control monitoring software. Trimble 4D Control software collects, processes, visualizes and analyzes the data of all monitoring sensors installed at the Victoria Dam and populates the results in real-time through an intuitive web interface. The software also issues alarms automatically whenever the system detects movement outside of user determined, acceptable parameters and sends status reports at user defined intervals.
Optical monitoring—setup of prisms and robotic total stations
Because of the double curvature of the Victoria Dam wall and often rainy conditions in the area, installing the required monitoring instrumentation across the dam was quite challenging. To start, the team had to develop a safe method to install the instrumentation, which included the construction of a gantry-like system suspended from a crane. This setup allowed an engineer to reach the wall of the dam safely to install the components, even at its most concave shape. The team installed 72 monitoring prisms set across the dam wall and on the dam crest next to the overflow gates. 48 of these prisms were placed at the same locations as the pre-existing survey targets, and 24 were added at new locations. In addition to the prisms at the dam, 40 prisms were installed on the left bank of the dam and 32 on the right bank.
During installation, the team also set up 64 millimeter (2.5 inch) prisms as part of the control network for the Trimble total stations, comprised of four points per station. The Trimble S9 total stations collect data measurements automatically for consistent and reliable data capture of all movement across the dam. Today, the total stations are scheduled to take a two-face observation of all prisms every three hours, which takes approximately 20 minutes. The collected data is then sent to Trimble 4D Control software for processing, analysis and visualization.
GNSS and water level monitoring—setup of GNSS receivers and piezometers
To provide redundancy to prism monitoring and to monitor the stability of the control network, GNSS monitoring was integrated into the system. The team installed three Trimble NetR9 Ti-M GNSS receivers on the dam crest and one as a base station in the control center building.
For integrated data processing, each GNSS antenna is co-located with a prism. All GNSS receivers on the dam crest transmit the observation data to the control center over Wi-Fi with a backup power source completing each GNSS station.
Amongst other sensors, the team also incorporated vibrating wire piezometers and a wireless data logger system to automatically read water levels. The wireless data logger transmits readings from close to the center of the dam crest to the control center building where the server hosting the system’s monitoring software is located. Currently,
the GNSS processing interval is set to three hours, while the data logger of the piezometers sends new data sets once per hour.
Bringing it all together—Trimble 4D Control monitoring software
The heart of the monitoring system is Trimble 4D Control monitoring software. Victoria Dam project leaders decided to install Trimble 4D Control on a server in the dam’s control center. The software processes data from optical total stations, GNSS receivers, geotechnical and other types of sensors. The historic monitoring data was imported into the software to analyze the behavior of the dam since it was erected. The manually collected historic data, the new real-time raw data, as well as the processed results allow project engineers to apply additional, customized calculations to the sensor data.
In total, data from 479 sensors is pulled into the Trimble monitoring software. Because the data can be collected and correlated in one platform, today’s dam engineers have a much better understanding of the structure’s history and transitions over time.
Improved monitoring leads to enhanced analysis
With the implementation of an automated monitoring system, Victoria Dam engineers now have a much more comprehensive and accurate collection of movement data at their fingertips. The team can focus their efforts on detailed analysis, predicting future behavior and continually studying the behavior of the dam with the added security of the system’s automated alarm system that alerts them to any changes to the dam exceeding set thresholds. The real-time, and now accurate, data allows the team to determine temperature and water level effects, and their influence on temporary movements, as well as permanent deformations. Among other observations made since the adoption of Trimble equipment, the team has noticed irreversible swelling of the concrete of the dam, which will continue to be observed.
Commenting on the new monitoring system post-installation, Er. Arrupola observed, “Working with Trimble’s automated, real-time geodetic GNSS monitoring data, combined with automated water level readings, has enabled us to establish a more complete and more accurate method for monitoring movement, reservoir crest levels and possible swelling of the Victoria Dam.”
By Brian Baker, P.E. and John McCarthy, Sc.D., C.I.H.
With the 2019-2020 school year cut dramatically short by the COVID-19 pandemic, public and private school systems and higher education institutions across the nation are exploring strategies today to prepare their buildings for a safe return to school this fall. Appropriately operating and maintained HVAC systems will play a critical role in creating a safe environment—and in building trust from staff and parents as these buildings are reoccupied.
As the Philadelphia Federation of Teachers recently learned from a 13,000-member survey, teachers are adamant that they will not return to school until facilities are in adequate condition. Schools that do not have a plan in place for a safe reopening will be hard-pressed to bring faculty and students back to the classroom. This plan should also address occupant perceptions of an unsafe building that may become conflated with COVID-19.
While there are abundant recommendations for reopening schools, it will be important that each school address their specific mechanical needs based on available resources, school demographics and specific building characteristics to create an effective approach to achieve their safe reopening and re-occupancy. Further, schools should periodically reassess their plans as communities move into different phases of reopening and deeper knowledge of response to COVID-19 becomes available.
A varied response
Across the board, schools are being advised to create layered control strategies, focusing on de-densifying classrooms, increasing physical spacing, improving ventilation, upgrading filtration, and considering supplemental air cleaning. Increased ventilation of spaces using clean air has proven to be an important and effective tool in helping prevent the spread of COVID-19 as it dilutes the concentrations of the virus in the air. Although Centers for Disease Control and Prevention (CDC) recommendations focus largely on disinfection and social distancing protocols, it offers brief guidance on school mechanical systems:
“Ensure ventilation systems operate properly and increase circulation of outdoor air as much as possible, for example by opening windows and doors. Do not open windows and doors if doing so poses a safety or health risk (e.g., risk of falling, triggering asthma symptoms) to children using the facility.”
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) provides more robust guidance to help schools identify specific opportunities for increasing ventilation. However, it’s important to note this guidance is being updated on an ongoing basis on the ASHRAE website, www.ashrae.org, as research around SARS-CoV-2 evolves.
The challenge, of course, with this broad advice is that there are a wide variety of natural, mechanical (both local and central) and hybrid mechanical systems operating in schools across the country. Moreover, many older schools, particularly public K-8th grade facilities, may be challenged in achieving adequate air distribution in the classrooms due to the age and limitations of their HVAC systems. Many of these systems may struggle to meet pre-COVID code requirements or ASHRAE recommended ventilation rates, as highlighted in a June 2020 Government Accountability Office report. This report concluded that more than 40 percent of the nation’s school districts need to update or replace systems, including HVAC and plumbing, in at least half of their schools. That amounts to approximately 36,000 schools beginning their COVID-19 response plan at a disadvantage.
However, this report also offers a starting place. Schools must begin by examining their own ventilation systems for maintenance needs and opportunities to increase ventilation. HVAC and other routine maintenance will become absolutely critical in creating a safe environment.
Must-do maintenance for HVAC equipment
Today, school facility managers have an incredibly strong and very valid case for growing their maintenance budget, so this is no time to hold back on inspections and identifying needed corrections or delaying preventive maintenance.
The first step is to begin with a review of existing systems to ensure they’re performing as intended. That includes examining air handling systems to make sure dampers are connected, fan belts are in good condition and appropriately tensioned, cooling and heating coils are functional and working appropriately, filters are being maintained, etc. This also includes ensuring general cleanliness of units, condensate drain pans, and related components. Further, knowing the actual flowrates for both outdoor air and recirculated air for each space that is intended for reoccupancy is essential in helping decide upon allowable class sizes.
Now is also the time to review common historic complaints about indoor air quality to identify patterns or problem areas. Any existing maintenance concerns must be addressed because they can give the impression of poor indoor air quality and erode faculty and parent trust in the building’s safety.
Today’s maintenance activities should also include putting a plan in place for managing both routine preventive maintenance as well as the actions that may be needed to address potential system trade-offs that may be associated with increasing ventilation rates. The most significant of these is likely be to thermal comfort. By increasing outdoor air ventilation beyond design limitations, you risk sacrificing comfortable temperature and indoor humidity levels. More than uncomfortable, this could heighten occupant concerns about the overall health and safety of the building.
In addition, there is the potential that increasing outside air ventilation without accompanying dehumidification can increase the likelihood of condensation on interior building components such as piping and ductwork. This can lead to the deterioration of building materials and the potential for future mold problems. Working with your HVAC engineer can help maintenance teams prepare for possible implications of increasing outdoor air ventilation through building air handling systems.
It’s also critical that facilities staff work closely with school administrators to keep abreast of the potential for reduced occupancy loads. Many school systems are evaluating partially digital schedules to reduce the number of students in a facility at a given time, thereby increasing the ability to keep adequate social distance between people. This reduced occupancy will improve the effectiveness of ventilation given that reduced occupancy means less potential contaminant or viral sources within the space as well as essentially increasing outdoor air ventilation rates per person, based on the lower number of occupants in the space.
Address shutdown-specific risks
CDC recommends specific actions be implemented by facilities staff if the building or systems were shut down, or usage was dramatically curtailed, for prolonged periods of time prior to re-occupying. Unless there was a program in place during the shutdown to regularly “flush” water systems, potential Legionella contamination, must be addressed now. Stagnant water can result in ideal conditions for bacteria like Legionella to grow. While Legionnaire’s disease poses its own risks, it’s important to note that it presents symptoms similar to those seen in COVID-19-infected patients and similarly affects vulnerable populations. Addressing Legionella is a critical safety step and will also reduce the risk of another school closure.
The CDC outlines several steps to take to minimize the risk of Legionella prior to reopening a school facility. The first step should be to create a water management plan that identifies high risk areas for water to stagnate, such as dead legs or unused taps or showers, and outlines steps to correct each problem.
Next, flush the building’s water systems with all terminal devices on a branch opened at the same time for a minimum of five minutes. Ensure hot water systems reach the maximum heat available. If these systems have not been flushed throughout the shutdown, there is a risk of inviting residual bacteria into the area where the test is being performed. In this case, be sure to work in a well-ventilated area and wear appropriate personal protective equipment, including a properly fitted N95 respirator.
Finally, perform cleaning in all areas where stagnant water is possible. This includes clearing running drains to eliminate standing water, cleaning gym and dormitory showers and checking cooling towers for proper operation and chemical treatment for scale, corrosion and biocide. For buildings or populations at highest risk, consider proactive sampling for Legionella.
Options for filtration and air cleaning
While maintenance will play a critical role in supporting higher levels of ventilation, schools are also looking to invest in other products to strengthen their infection control response.
ASHRAE advises increasing filtration at the air handling unit to limit the spread of viral particles recirculated through the return air system. The association’s guidance suggests MERV 13 filters as preferable as these filters are able to capture particles as small as 0.3-1.0 microns with reasonable efficiency. However, few of the older school HVAC systems will be able to accommodate the recommended minimum MERV 13 filters. Higher efficiency filters add a restriction to the airflow and without compensating for this restriction, result in a decrease in airflow. To make up for this, schools are looking to utilize portable air filters with HEPA filtration for each classroom. If this is an option your school is considering, it’s best to act now. Obtaining HEPA filters and portable purifiers could become more challenging in the fall as demand increases.
In addition, some schools are exploring UV-C and ionization solutions as a potential avenue for limiting the spread of viral particles. ASHRAE provides guidance on the use of UV-C for in-duct air disinfection and surface disinfection and although there are specific applications where this technology is effective in degrading viruses, the products are not considered plug-and-play solutions. To be effective, a UV-C system must be appropriately designed into the existing HVAC system(s) and its output matched with the system’s airflow. Consult an experienced design professional if considering the use of UV-C. Regarding ionization, there is limited information about the effectiveness of this technology in commercial HVAC systems and this should be considered when evaluating its use and installation costs.
Budget for critical improvements
While recommended maintenance activities may stretch school budgets, these activities are critical to ensure student and staff safety. For many schools, it will be a matter of bringing mechanical systems up to current code performance and catching up on too long deferred maintenance. For others, it may mean investing in the staff to perform routine maintenance or forging relationships with HVAC contractors or consultants to supplement the in-house team.
Schools are also likely to see an uptick in operational costs. Among other recommendations ASHRAE advises extending HVAC system operating hours compared to typical occupied hours to provide an increased ventilation rate prior to and after occupants leave the building. This increased energy use can drive up energy bills.
However, this is but one more reason why it is critical to outline today the steps necessary to safely reopen and identify the potential impacts of each step. Preparing early gives schools time to brace for budget impacts. It also gives facilities managers time to help project where investments are most needed and how to minimize the overall impact on the building. By preparing today, schools can minimize the impact of COVID-19 on their budgets and their communities and create a building environment that is both welcoming and safe for its occupants.
By Steve Roloff, P.E., LEED AP
The Hamel Music Center at the University of Wisconsin-Madison is a world-class concert hall that required extreme accuracy in its design. This one-of-a kind music facility required structural and acoustic designs that would work together. Teamwork and expert knowledge resulted in just that: extraordinary sound quality and listening experiences for university students, faculty and community patrons. Many experts gave careful consideration to the facility’s structural strength and support, reverberation and sound isolation, acoustical performance and materials used, among other specifications.
A School in Need
The Mead Witter School of Music was housed within a campus building constructed in 1969. Over the years, significant building changes to keep pace with the times had not occurred, outside of a major asbestos removal in the 1990s. Staff were teaching, and students were learning in an environment that begged for physical and functional upgrades as the school continued to grow. The need for sound isolation was paramount to the musicians’ achievements of excellence.
Predevelopment for a new School of Music with a modern environment began in the mid-2000s. While the goal for building occupancy was early 2017, multiple setbacks left the project on hold until many generous donor contributions allowed the project to resume in 2014.
Beyond budgetary considerations, the new building would need to connect the campus to its surrounding community. But how would this connection be achieved? In order to create this new arts corridor, the Hamel Music Center would be situated along busy University Avenue. Next door to the Hamel Music Center stands the Chazen Museum of Art, University Theatre across the street, and the Wisconsin Union and Wisconsin Union Theater down the block and around the corner.
The team’s goal was to design a building fit for rehearsing and performing. Acoustics and sound isolation needed to be top tier for exceptional performances unlike any other. Our structural engineering team faced challenges of isolating sound stemming from busy pedestrian and vehicular traffic (including ambulances) along University Avenue, which is one of the city of Madison’s most traveled vehicular streets. Additionally, noise pollution was expected from doors opening and closing, chatter within the lobby, loud HVAC systems, and music played in adjacent halls. Each of the music center’s halls (concert, recital and rehearsal) and its lobby needed to be isolated from one another, like a vault for acoustics.
Solutions to highly unique problems were inventive, such as the use of acoustical isolation joints (AIJs) that were essential to providing superior sound isolation around the three individual halls. Acoustical isolated construction, an acoustical coffer system and other techniques were also employed.The concert hall is the largest hall in the Hamel Music Center. The hall applies many creative, smart techniques to maximize the fine art of acoustics. Circles, better known as an acoustical coffer system, line the walls and ceiling to absorb and reflect sound. Two hidden, large (each capable of fitting 14 public transportation buses!) reverberation chambers flank either side of the stage. Curved balconies redirect sound back to the audience.
Unique Sound Treatments
The overall structural design that worked perfectly for acoustical requirements and sound isolation was to essentially place three separate buildings within one larger building. The concert, recital and rehearsal halls are self-supporting, using independent lateral truss systems, and isolated from the large overall building (including the main lobby and its required support space) via the acoustical isolation joint.
The two-inch acoustical joint assembly may be small but its impact is critical to the structure: It essentially separates the concert hall from the rest of the building framing into, and supported by, the 16-inch concrete walls surrounding and serving as part of the hall’s structural system.
A typical joint consists of steel beams connected to a steel haunch welded to an embedded plate placed at the outside face of the hall’s concrete wall. Direct steel-to-steel contact would transmit noise and vibration in the finished building and this needed to be avoided. To create the isolated joint, a neoprene bearing pad was added on top of the steel haunch on which the in-framing steel beam sat via a steel bearing plate atop the neoprene pad. To secure this connection, a pair of threaded studs welded to the haunch bolted down the beam.
To avoid direct contact of the stud’s washer and nut to the in-framing beam, a neoprene washer was added between the beam and stud washer. But the problem was not fully resolved, as the steel-on-steel contact could still occur between the studs and the beam and its bearing plate. To further eliminate noise transfer, a neoprene bushing surrounded the weld stud. This resulted in a connection design in which no steel touched and eliminated the possibility of reverberation. (However, these connections were permitted to transfer loads.) The structural design incorporated hundreds of these joints.
Beyond this joint assembly, the concert hall’s perimeter concrete walls, soaring to a 70-foot maximum height, easily addressed lateral stability needs. The structure outside of the hall was attached to the hall’s walls via the acoustical isolation joint. This connection eliminated the need for unsightly and costly columns in the structural design. Instead, the column-free areas offer unobstructed views of concert performers.
The recital and rehearsal halls utilized double-wall construction. For the recital hall, this consisted of an exterior precast wall panel in conjunction with an interior acoustically isolated concrete masonry unit wall. Similarly, the rehearsal hall’s perimeter used a precast panel but with an acoustically isolated interior drywall system instead.
An acoustical coffer system (a series of strategically sized and strategically placed concave and partially or fully hollow circles) line the concert hall’s walls. These sizable circles treat sound by absorbing and reflecting it, along with the hidden reverberation chamber areas where sound actually passes through. The coffer system is visible and fits in beautifully with the rest of the hall’s aesthetics.An aerial view of the project: The largest area with circles in the concrete is the concert hall; both sides have large reverberation chambers for acoustic treatment. Adjacent to University Avenue in Madison, Wis., are the recital hall (left) and rehearsal hall (right).
Structural Design Enhances Building Aesthetics
The Hamel Music Center’s second floor lobby hangs from the roof structure to create a column-free area at the main lobby and a floating lobby appearance, with a monumental staircase connecting the two levels. The lobby combines ductwork laterally into a curtain-wall system, disguising the necessary pipes while also incorporating them in an aesthetically pleasing way. To achieve a crack-free floor appearance, the structural design called for a 4-inch drop of the structural concrete slab floor. The floor was infilled later with a colored concrete topping slab properly jointed and separated from the structural floor.
Unique to the rehearsal hall is its view to the activity on bustling University Avenue. A corner of this hall’s double walls was cut open and, in its place, sit a double set of windows, providing musicians and pedestrians a view of the other. The design application prevents outside noise from entering the hall and allows the music to remain solely within the rehearsal space. Double cantilevers and leaning steel columns were designed to support the exterior’s zig-zag precast panels that float over this corner condition.
Both recital and rehearsal halls feature distinctive exterior wall shaping. Beyond aesthetics, these shaped precast panels are sloped in different directions and used as part of the mass required for the acoustic outside box wall system. In order to make the shapes, molds were designed exclusively for this project. A lateral truss system provides the support required for these walls, enabling them to stand freely.Concert hall acoustical isolation joint Recital hall sound wall isolation detail
A New Star on Campus
Design and construction occurred between 2014 and 2019 at a total cost of $55.8 million. And in October 2019, the Hamel Music Center celebrated its grand opening. The new recital hall’s capacity nearly doubles that of the old recital hall. The concert hall’s stage, unlike that of its predecessor, comfortably fits a large group of student-musicians.
Connection to the community happens through the Hamel Music Center. Increased social connections are a direct result of the new building. Passersby on University Avenue can catch a glimpse of students at practice in the Kaufman Rehearsal Hall. The school’s former recital hall used to host 160 performances a year, but the new Collins Recital Hall is planned to deliver more than 350 performances year after year. Community music instructors may hold lessons within the building, and occasional music guests may hold an event here. Digital streaming technology further connects the students’ music to communities throughout Wisconsin—and far beyond.
The isolation of the concert, recital and rehearsal halls from one another is completely unlike that of other auditorium and performance hall designs. Indeed, the University of Wisconsin–Madison’s School of Music Hamel Music Center is a rare project that calls for the fine art of acoustics.
Steve Roloff, P.E., LEED AP, structural group leader at raSmith, served as the project manager and senior structural engineer for the Hamel Music Center project. He has more than 35 years of structural engineering experience. raSmith is a multi-disciplinary consulting firm comprising civil engineers, structural engineers, land surveyors, development managers, landscape architects, and ecologists.
The post Hamel Music Center Uniquely Isolates Sound, Producing Outstanding Performances appeared first on Civil + Structural Engineer magazine.
By Carlo Taddei, PE
At an institution steeped in tradition, engineering has been in the DNA of Texas A&M University (TAMU) since opening its doors in 1876 as the Agricultural and Mechanical College of Texas. Combining the tradition of engineering education with two of the university’s core values, excellence and leadership, TAMU seeks to establish itself as the nation’s preeminent institution for engineering research and education and lead the charge in transforming engineering education. The College of Engineering (COE) is now the largest college within the TAMU College Station campus and largest undergraduate engineering program in the nation with 22 engineering majors across 14 departments and over 20,000 students.
According to the President’s Council on Science and Technology, it is estimated that more than one million additional science, technology, engineering, and mathematics (STEM) degrees will be needed in the next decade. The Texas Workforce Commission also projects the need for 62,000 more engineers in the next decade. To address the critical and growing demand for engineers, the TAMU COE launched the 25 By 25 initiative in 2013, which aims to increase enrollment from 14,000 students in 2013 to 25,000 students by 2025. The initiative was designed to enhance the quality of engineering education and shape the engineer of the future by transforming the engineering classroom into a 21st century model focused on technology-enabled learning, hands-on projects, and collaborative, multidisciplinary learning spaces.
As stated by Dr. M. Katherine Banks, Dean of Engineering, “The 25 By 25 initiative is not just about increasing enrollment, but also about providing better instruction and opportunities. We will transform engineering education to mold the engineer of the future.”
The first major step toward this goal was the completion of the Zachry Engineering Education Complex (ZACH) which is focused entirely on undergraduate education. The ZACH stands at 525,000 SF and was achieved by renovating the original 300,000 SF building, adding a vertical expansion onto the building, and adding two, new five-story lateral additions. As a company that employs many graduates of the TAMU Department of Civil Engineering, we were honored to provide structural and civil engineering, and surveying services to TreanorHL Architects on this highly important project.Reconstruction of Interior Core Including New Learning Stair
Originally opened in 1972, the H.B. Zachry Engineering Center served an enrollment of 15,000 students. The original Zachry building fit the traditional model of 1970s academic facilities: faculty offices, dean’s suite, enclosed research laboratories, tiered classrooms, large lecture halls, and underutilized atrium space. While the building was iconic for engineering students, it lacked energy and failed to provide the multi-disciplinary, interaction, and collaboration spaces that truly enable engineering students to succeed in today’s environment.
As was common in the 1960s and 1970s, the building was designed in the brutalist style of architecture with large monochromatic precast concrete panels covering approximately 75 percent of the building exterior, which many considered to be an eye-sore. The structure did have some cutting edge design techniques and creative solutions, such as the load-bearing precast concrete façade, two-way post-tensioned joist “waffle” slabs, precast concrete double tees for the basement wall, Vierendeel steel trusses across the atrium clerestory, and was designed for vertical expansion. However, the large sloped-floor lecture hall, tiered classrooms, and large atrium posed challenges for reconfiguring to accommodate smaller active learning classrooms and lab space.
The solid interior finishes, compartmentalized interior layout, and precast façade did not provide transparency or foster excitement about engineering. The first question posed to us at the project kick-off meeting was “How are you going to make all of the exterior precast concrete disappear?” It was made abundantly clear to us that the COE did not want to see any of the original precast concrete façade. This created a significant challenge because the precast concrete served as the perimeter support for the concrete superstructure. This set the tone for the project and we quickly realized that the project was going to have some unique challenges that would allow us to showcase our ingenuity and creativity.
The project was broken down into three distinct phases: Deconstruction, Reconstruction, and Expansion.Completed Active Learning (Seating) Stair and Skyligh. Photo: Randy Braley.
Deconstruction and Site Challenges
The first phase of the project involved issuing a demolition package to cover removal of all building finishes, HVAC services, and major structural demolition. In addition to removing the load-bearing precast concrete panels, structural demolition also involved the large sloped-floor lecture halls, steel Vierendeel trusses at the clerestory, interior stairs, mezzanine structure, and portions of the existing floors and roof.
The precast concrete panels were 10-feet wide C-shaped columns at 16-feet, six inches on-center with a void space in the middle that served as mechanical exhaust. The precast columns were supported by cast-in-place concrete columns between the basement and level 1. To further complicate matters, the existing grade was approximately seven feet above level 1 on the north, east and west sides of the building and the main entrance(s) to the building occurred at level 2. The existing basement wall was located eight feet beyond the building face and consisted of precast concrete double-tees. A structurally spanning concrete sidewalk was present, which braced the basement wall back to the building structure. Where grade extended above level 1, a concrete upturned beam supported the precast columns and structural sidewalk.
The new building program called for the grade to be lowered and entry to the building relocated to level 1 on the east, west and south sides. This required the existing structural sidewalks, basement walls, and upturned beams to be demolished above level 1. Permanent steel shoring was installed to laterally brace the existing basement wall back to the existing building columns during demolition.
In order to remove the precast concrete columns without having to temporarily shore the structure, a new permanent support system was designed consisting of a 16 inch thick cast-in-place concrete basement wall along the north, east and west sides of the building and steel columns to support the floors and roof. The grade along the south side was unchanged, so steel transfer girders were designed to span between existing building columns to support the new steel columns. The steel columns were fabricated with steel “haunches” on the inside face, which permitted the columns to be installed outboard of the floor structure and run full height of the building.
Close coordination with the construction manager was required to ensure work was properly sequenced since columns had to be “fished” down the void space in the precast columns with the steel haunches turned parallel to the floor spandrel. Once the columns reached the bottom, they were rotated 90-degrees to position the haunches below the floor framing. After the steel columns were plumb and the haunches shimmed, the precast columns were demolished from the top down.
Once the precast columns were removed, steel beams were installed between the steel columns around the perimeter of the building at each level, creating a steel “exoskeleton”. Concrete slabs were then installed at each level to extend the floor out to support the new façade, which was outboard of the new steel framing.
As the new focus of the ZACH was aimed at “learning by doing,” the large lecture halls in the original building were replaced with smaller active learning classrooms. This required reconfiguring the center core of the building, including demolition of the large concrete-framed lecture halls. Since the main entrances to the building were reestablished at level 1, a 12,000 SF section of the post-tensioned waffle slab at level 2 was demolished to extend the new central atrium to level 1.
As part of the teaching and research program, the original building housed a 60-year-old, 5W nuclear reactor that had to remain operational during the demolition phase until it could be decommissioned and relocated. This required special detailing and sequencing of demolition to work around the reactor room to avoid disturbance.Completed Building Southeast Corner Photo: Randy Braley.
The interior core of the building was reconstructed with structural steel infill framing and a new central “learning stair” between levels 1 and 3 to allow students to study and collaborate. Steel bridges at each level connect the two sides of the atrium and support the stairs. The new infill structure had to be carefully planned and new columns strategically placed to minimize impact on the existing structure. New steel wide-flange columns were “punched” through the post-tensioned waffle slab at level 1 and carried down to the basement. New concrete transfer beams and drilled under-reamed piers were installed to support the new columns.
With the precast façade removed, new limestone cladding and curtainwall was introduced to provide a more transparent and aesthetically appealing structure.
Per the original construction documents, the building was designed to accommodate two levels of vertical expansion. JQ verified this assumption by analysis of the structural framing. To better relate with the five-story building additions on the north and south sides, only a portion of the existing building was vertically expanded. Structural steel was used for the vertical expansion to reduce weight. Approximately half (32,600 SF) of the existing roof was converted into a new fifth floor level and approximately 6,600 SF consisted of a two-story expansion to accommodate a mechanical penthouse.
In order to bring natural light into the building, a new 3,500 SF split-level skylight was designed to run down the spine and span across the central atrium. The 165-foot long skylight begins at the existing roof level (level 5) at the west end, turns vertical up the building face and ends at level 6. The skylight has a tapered design with the west end four feet wide and the east end 42 feet wide. A 2,700 SF section of the existing concrete roof structure had to be removed to accommodate the skylight. The upper skylight support frame consisted of a “tabletop” roof with a center ridge and hipped corners that were rigidly connected for lateral stability. The skylight support elements consisted of hollow structural shapes (HSS).
The two building additions occurred on the north and south ends of the original Zachry building and added 185,000 SF over five levels. The north addition contained a 9,500 SF mechanical penthouse (level 6) even with the vertical expansion over the existing building. The two building additions are cast-in-place concrete superstructures with a wide-module pan joist floor system.
A major challenge for the additions was the location of new columns and foundations in proximity to the existing building. The foundation system for the additions and existing building consisted of under-reamed piers which were large due to the high dead load from the concrete structure. The columns were pulled back approximately 10 feet from the existing building to accommodate large MEP chases to route utilities from the basement level. Even with the offset columns, additional foundation offsets and deep cantilevered strap beams were required to support the columns to avoid conflicts with the existing piers.
To achieve the aesthetic quality and daylighting strategies that the architect desired, the project had an abundance of steel sunshades, screens, canopies, and trellises. The trellis over the south addition had the longest cantilever, 36 feet with a back-span of only 22 feet. The cantilevered beam consisted of a W44x262 and suspended a three-story “billboard” wall clad with perforated metal panels and contained cantilevered 18 inch square HSS beams at each level to resist out-of-plane wind loading.Completed Building, Food Truck Park and Engineering Quad. Photo: Randy Braley.
By utilizing over 80 percent of the original 300,000 SF structure, construction waste was reduced, and carbon emissions significantly decreased thereby reducing negative environmental impact of traditional new construction. The ZACH is now the largest academic building on campus at 525,000 SF and is accessible to engineering students 24/7, which increases the utilization factor and efficiency of the building. The ZACH is large enough to fit two Boeing 747’s placed end to end!
The project also features a 13,000 SF landscaped (green) roof and a 2-acre outdoor green space known as the Engineering Quadrangle (E-Quad). The E-Quad contains a food truck park, rain garden, engineering-focused artwork, seating benches, and picnic pavilions, uniting students from all around campus. Both green spaces contain sustainable materials and low-maintenance native planting.
Rethinking Engineering Education
The facility contains technology-enhanced active-learning studios, interdisciplinary laboratories, 60,000 SF of makerspace (a design center containing machining and fabrication equipment), a student career center, study and gathering spaces, engineering-inspired art, and a green roof where outdoor lectures can be conducted. Interior floor-to-ceiling storefront provides visual access into the fabrication center and engineering laboratories to put engineering education and experiments on full display. Both the function of the facility and the building itself present a positive public image of engineering excellence. As Michael K. Young, President of Texas A&M University, stated at the dedication ceremony, the Zachry Engineering Education Complex is a “stunning feat of engineering.”
The ZACH is not only a display of engineering excellence but a world class facility that brings engineering to the forefront and further cements Texas A&M University’s status as a national leader in engineering education. The building itself serves as a recruiting tool attracting the best and brightest students and professors to TAMU for generations to come.
Carlo Taddei, PE is a Principal, Higher Education and K-12 Market Sector Leader, and Fort Worth Office Lead for JQ Engineering. He served as Engineer of Record for the TAMU ZEEC. Founded in 1984, JQ provides structural and civil engineering, geospatial and facility performance services throughout the United States. The firm is considered a leader in engineering design innovation and technology to support its complex, multi-state and multi-market projects. Nationally, JQ has been recognized as a “Best Place to Work” and as a “Hot Firm” by Zweig Group. JQ has offices in Austin, Dallas, Fort Worth, Houston, Lubbock, and San Antonio. For more information, visit the company’s website at: www.jqeng.com.
The Conrad Washington, DC, the capstone building for the CityCenterDC development, presented several unusual challenges to the design and construction team. The combination of a tight complicated site, the need for large column-free ballrooms, and a below-grade loading dock under the hotel tower compelled the team to selectively use structural steel in a predominantly concrete structure to solve design challenges.
The hotel massing forms a trapezoidal shape for a podium structure up to Level 3. There the floor plate transitions to a pentagon shape around a central atrium with two adjacent 8-story wings featuring post-tensioned flat slab construction at the hotel rooms. The pentagon and wings form a layout reminiscent of an awareness ribbon (Figure 1). The full-height atrium is topped by a skylight and concrete slab, supported by a two-way steel beam system spanning 75 feet by 85 feet (Figure 2). W36 beams spaced at approximately 10 feet in each direction were moment-connected to each other to complete the multi-directional beam system. A portion of the concrete floor slab below was hung from the skylight steel to create an extended slab edge over the atrium at the highest occupied floor. The steel dual-beam system provided minimal structural depth over the long-span atrium.
To fit the full building program on the available footprint and within the design architect’s intent, the design team was required to transfer all but five of the 77 hotel tower columns and many of the concrete shear walls at the third level. To maximize ceiling height within the junior and grand ballrooms, and amenity levels below, the transfer girders were limited in depth to 6 feet. To meet these ceiling height requirements, a steel-framed transfer floor was required with steel plate girders consisting of 4-inch-thick by 4-foot-wide flanges, spanning 55 feet over the grand ballroom and supporting up to four columns. With some plate girder sections weighing over 1,300 pounds/foot, many of the transfer girders required splices with complete joint penetration (CJP) welded and heavy-bolted beam moment connections due to transportation and tower crane limitations (Figure 3).
At steel framing near the tower elevators, the depth of the plate girders was sufficient to accommodate the hotel elevator pits. The pit floors were suspended from the bottom flanges of the plate girders. Vertical reinforcement for concrete columns and walls above were welded to the transfer beam top flange to transfer loads to the podium slab efficiently. Due to the dramatic differences in column arrangements above and below the podium, many framing conditions required cantilevered transfer beams or other unique framing configurations. The unique and deep framing required careful coordination between the architects’ finished ceiling and MEP systems, resulting in many web penetrations through steel members. Perimeter podium columns were tightly spaced and located as close to the perimeter as possible to avoid special framing and detailing of the store-front façade.
The settlement and tilt of the superstructure due to transfer girder deflection had to be controlled during construction. A custom “boot” made of 6½-inch-thick steel plates in a horseshoe shape was designed as the base of multiple columns just above the third-floor framing (Figure 4). The center of the boot created room for two hydraulic jacks while the sides allowed for steel shims to lock the column in place. The settlement at each column was monitored as the above post-tensioned (PT) concrete floors were constructed. As determined by slab analysis of the PT slabs, a displacement threshold of 1⁄8 inch of vertical displacement was used to determine when jacking was necessary. Hydraulic jacks were inserted into the boot, and the entire tower concrete frame was then jacked back to a level condition. The 1⁄8-inch vertical displacement limit resulted in about every third floor requiring column jacking, closely aligning with the structural analysis predictions. Once the concrete tower was fully constructed, steel plate shims were inserted and welded inside the steel boot assembly; the jacks were removed, and the void grouted solid to transfer the final design live load to the supporting transfer beam. The column jacking permitted the use of more economical shallow transfer beams as the majority of the dead load deflection could be jacked back to level. This allowed the slab to be designed for a maximum of L/600 live load column vertical settlement where “L” was the shortest distance between adjacent columns.
Special attention was necessary to coordinate detailing requirements at the interface of steel and concrete, especially at embed plates, bearing plates, and transfer beams, as the different materials had different fabrication and erection tolerances. In most cases, traditional cast-in-place embed plates and beam end connections were not adequate to transfer the high shear loads. Many of the steel beams were detailed to bear directly on a grout pad and embed bearing plate at the top of the concrete columns. For beams with significant end rotation, elastomeric pads were provided below the beam bottom flange to permit member rotation and avoid excessive moment transfer to the supporting column.
The lateral system used to resist the wind and seismic loads consisted of ordinary reinforced concrete shear walls. Due to multiple transfers and offsets in the lateral system, the transfer of large forces through the podium level diaphragm required local slab thickening and diaphragm reinforcement. Despite the low seismicity (seismic design category B), the horizontal out-of-plane offset irregularities and nonparallel system irregularities required portions of the lateral system to be designed considering seismic overstrength, controlling detailing and certain aspects of the lateral design such as collector and chord reinforcement within the diaphragms.
A porte-cochere at the hotel entrance is supported by a slab on metal deck, steel framing, and a 23.5-foot-deep, floor-to-floor truss spanning 120 feet located at a reentrant corner of the building (Figure 5). Steel framing at the truss top chord supports up to four feet of soil and landscape plantings on an outdoor terrace above. The truss diagonal members (heavy W14 shapes) were wrapped with gypsum board to provide the required fire-rating and were architecturally expressed as a design feature in the pre-function space of the hotel’s ballrooms. The anticipated deflections for the long span truss required careful coordination with the contractor, particularly concerning curtain wall detailing and construction sequencing. Pre-loading and sequencing of construction options were investigated to determine that expected movements of the truss would remain within the curtain wall design parameters.
The building structure is founded on approximately 1,060 eighteen-inch-diameter auger cast piles. Several pile caps provide support of multiple columns in groups of as many as 66 piles. Many of the pile caps required mass concrete operations and temperature monitoring to control temperature during placement and curing, and to minimize the risk of delayed ettringite formation due to the caps being up to 7 feet thick. Foundations along the property line were designed to accommodate future construction of an adjoining building basement below the lowest level of the building. The lowest level of the garage is 40 feet below the water table. To maintain a dry garage, waterproofing was provided on the outside of the foundation walls, and an underslab drainage system with continuous pumping was installed. A new loading dock and tunnel at the second story below grade connect the hotel to the adjacent CityCenterDC complex. Columns above the loading dock and tunnel were supported on 4-foot-wide by 10-foot 10-inch-deep concrete transfer beams spanning 74 feet to allow for truck access to the loading dock. The concrete transfer beams required the use of mechanically spliced 75 ksi rebar utilizing multiple layers of top and bottom steel.
The below-grade levels are two-way conventionally reinforced concrete slabs with beams at specific locations for parking, loading docks, and mechanical spaces. Access to the parking levels is made through a corkscrew ramp at the northeast corner of the site. The ramp interrupts floor diaphragms that provide lateral support for the basement walls. Special analysis was required at the ramp and adjoining slabs to ensure lateral loads from the basement walls were resolved at the interrupted diaphragms. The section of the slab between the corkscrew ramp and the foundation wall was reinforced as a horizontal wall beam to span the entire ramp width laterally.
The creative use of structural steel (1,368 tons) in a predominantly concrete structure was critical to meeting program requirements and the architect’s design intent and essential in delivering the project on time. Careful detailing at the steel and concrete interface was required to accommodate different construction tolerances and large force transfers. Additionally, due to the complex massing transition, many types of advanced analysis were necessary to provide an optimal building structure.■
Repurposed shipping containers have taken root within the construction industry. What were once utilitarian boxes full of cargo out at sea are now seen across the United States and around the world as offices, living spaces, retail spaces, and multi-unit structures. The use of these steel cargo boxes as building materials continues to grow rapidly and, to keep up, structural engineers and the construction industry at large must learn to build these container-based structures with safety in mind.
This is the present challenge. A patchwork of regulations for shipping container structures has emerged, producing confusing and potentially conflicting information as local Authorities Having Jurisdiction (AHJs) have sought to develop specific standards. In some cases, the lack of definitive regulations has led industry participants to ignore building codes altogether, creating potentially unsafe structures. Imagine a construction worker getting trapped inside a container office due to poor structural welds. What if a cantilevered container structure were to collapse due to a lack of structural engineering approval? Tragedies like these would put lives in danger and bring permanent damage to the industry.
Fortunately, the International Code Council (ICC) is taking the necessary steps to create a safer future for container-based buildings. The ICC is dedicated to developing model codes and standards used in the design, build, and compliance process to construct safe, sustainable, affordable, and resilient structures. Most local governments trust the ICC’s suggested codes and adopt the International Building Code (IBC) into law. Working alongside the Modular Building Institute’s Container Task Force, which is comprised of various shipping container manufacturers and structural engineers, the ICC took steps to incorporate shipping container structures into the building code.
To that end, the ICC has published a new ICC Guideline, ICC G5 – 2019, which is intended “to help state and local jurisdictions – as well as owners, architects, builders, and engineers – in their assessment as to how to design, review, and approve such shipping containers as a building element.” All quotes herein are from this Guideline unless otherwise noted.
The ICC Guidelines break the container-based structures industry into four segments: temporary single units (e.g., construction offices), permanent single units (e.g., equipment enclosures), temporary multi-units (e.g., pop-up retail structures), and permanent multi-units (e.g., multi-family buildings). Because these four segments are distinctive, shipping container building codes should not be one-size-fits-all solutions. For example, a single unit ground level office should not be regulated as a multi-story apartment. The ICC Guidelines make it clear that permanent structures built from containers, “like any other building structure, are required to comply with the codes,” both non-structural and structural. However, for temporary structures, the ICC Guidelines state that they “may not be requiring full compliance with the provisions of the building code.”
Specific to structural code compliance, one of the critical problems is the lack of information on material properties and specifications for the steel elements of the container. The ICC Guidelines solve this problem by providing a section on Referenced Standards and demonstrate how the shipping container industry tests the structural integrity of each container. A Convention for Safe Containers (CSC) Safety Approval Plate, fastened to the exterior of the structure, distinguishes containers that are built, tested, and inspected against the ISO standards, providing the necessary data and information on the construction of the specific container. “A code official can reasonably rely on a data plate to confirm that a container was built and inspected to the appropriate ISO standard.” A container without a CSC Safety Approval Plate can and should be rejected by code officials.
The ICC Guidelines also address the interior of the containers and their wood flooring. What has caused concern for some is rooted in misunderstanding. The ICC Guidelines provide evidence supporting that it is highly unlikely that a contaminated container would make it into the marketplace, and they cite evidence proving that the chemicals used to treat the wood floors are harmful only to insects as a repellent, and not to humans.
The current Acceptance Criteria pertaining to shipping containers, ICC-ES AC462, is not meant for overall building code compliance but instead establishes the physical and chemical properties of the container. This regulation is not retroactive and, although it is the most utilized regulation, it is not the only path forward.
As the ICC Guidelines evolve into more definitive requirements, the ICC will provide a ratified amendment to Chapter 31 of the 2021 IBC. This new building code will incorporate shipping containers for the first time, and provide data for code officials and the industry to ensure these container-based buildings are structurally safe even when modified. Additionally, the code provides a roof exemption and a simplified structural design methodology for single unit containers.
Considering all the previously discussed guidelines, a future of a well-defined shipping container building code is becoming a reality. The adoption of these guidelines will allow the shipping container construction industry to evolve safely. It will ensure that each container structure is safe and that there is a starting framework to engage in proactive dialog. Now, one can imagine a future where container-based structures help in solving problems instead of creating them, possibly by providing affordable housing in major urban areas or extra space in overcrowded schools. A different picture results from well-regulated shipping container structures, one that comes with an abundance of benefits for the businesses and communities that use them.
To learn more about shipping container building code, read the ICC G5-2019 Guideline for Safe Use of ISO Intermodal Shipping Containers Repurposed as Buildings and Building Components (https://bit.ly/31ZD7o0) and the Modular Building Institute’s Safe Use and Compliance of Modified ISO Shipping Containers For Use as Buildings and Building Components white paper (https://bit.ly/36ikrit).■
The City Creek Center’s masonry façade is an example of a structural engineering project that used performance-based-design to improve upon conventional, mundane brick façade systems. Located in Salt Lake City, Utah, the project site encompasses 23 acres of land representing two large city blocks. It contains four residential buildings with 535 units, three office buildings, and 700,000 square feet of retail space. A creek runs through the site, thus the name. The exterior walls of the project are brick, precast concrete, and glass.
Eight architectural firms were involved in the project, but only one structural engineer of record, Magnusson Klemencic and Associates (MKA), Seattle. MKA approached KPFF Structural Engineers early in the project to assist in the design of the brick exterior walls.
As a structural engineer specializing in the design of facades or curtainwalls, including walls constructed of brick masonry, opportunities to design a project of this size rarely occurred during the author’s career. It has been a challenge to convince owners and architects to design brick walls before bidding and show those designs on a set of drawings, instead of specifying performance and requiring the contractor to design the wall. The City Creek project opened the door to this alternative delivery system.
Because of the complexity of the wall, all parties agreed, after much discussion, to include the wall design as part of the project design documents, allowing for a performance-based-design (PBD) method to be used.
Although several different masonry wall systems were used on the project, including reinforced veneer (structural brick veneer), the following describes the innovations on two of the six buildings. For these two buildings, a brick veneer on steel stud system (BV/SS) was selected (Figure 1).
The advantages of a performance-based-design include the ability to more precisely define the expected performance, increase the chance of achieving that performance, and allow for cost-reducing innovations that deviate from standard practice and/or prescriptive code compliance.
The first challenge was to convince the stakeholders to expand the structural engineering involvement to include performance-based-design. Eventually, all agreed that there were opportunities to customize the BV/SS system to reduce cost and to better meet the owner’s needs. The complexities of the walls helped drive the decision.
Although BV/SS walls are common, structural engineers typically are not involved in the design except for a limited analysis of the backup wall to determine the expected wall deflection (the codes and standards do not provide consistent criteria for the deflection limit). The applicable building codes for this project were the 2006 International Building Code (IBC), ASCE 7-05, Minimum Design Loads for Buildings and Other Structures, and TMS 402-05, Building Code Requirements and Specification for Masonry Structures. These codes contain limited brick veneer performance requirements, leaving considerable freedom to customize performance criteria.
Early in the process, the Owner, General Contractor, Construction Manager, and consultants were involved in discussions about wall performance. The wind and seismic loads were well defined, but the required performance was not. Since the project is located in a high seismic risk category, the seismic performance was a primary issue.
Seismic loads were divided into three intensity levels; 1) frequent event, 2) 500-year return period, and 3) 2⁄3 maximum considered. The engineer of record provided seismic displacements for each floor at each seismic level. Building wall elements were differentiated by location and geometry – flat or linear walls at the base and typical floors, corners at the base and typical floors, and parapets. Four levels of performance were defined: operational, immediate occupancy, life safety, and collapse.Operational (No damage) – Hairline cracking of masonry bed joints may exist, with or without a seismic event. Immediate Occupancy (Minor damage, repairable) – Failure of caulked joints and separation of window seals is expected and can be repaired. Cracking of masonry bed joints is expected. Some cracking of brick at corners. Some vertical cracking through brick units is likely but limited. Some separation of face shells from the wall and units from parapets and other appendages. Life Safety (Major damage, repairable) – Severe damage to portions of the wall and minor separation from the building, with no panel falling hazard. Collapse (Major damage, not repairable) – Large portions of the wall have substantial damage and create falling hazards.
Meeting the operational and immediate occupancy criteria for anticipated damage at the corners of the building presented a design challenge. A typical BV/SS wall would not meet the criteria at the corner. Differential floor-to-floor displacement would break the rigid brick corner. Isolation of brick corners can be accomplished by various strategies:Eliminate the brick corner and substitute another element, such as an aluminum plate. Provide a large expansion joint at the corner. Cantilever the backup system from one floor without attachment to the floor above. Build a reinforced veneer or reinforced brick panel that is supported on one floor without attachment to the floor above. Warp the backup and brick system by placing the attachment to the upper floor at a defined distance from the corner.
All options were considered. The decision was to use option 5. Options 1 thru 4 could have been developed by analysis without additional technical information. But the information to accomplish Option 5 was not available. Warping the masonry (a panel with 3 corners fixed and the fourth lifted or pushed perpendicular to the masonry surface) is not a common design problem, and no information was available. Consequently, it was decided to test the corner. A mockup panel was constructed and tested to obtain the information (Figure 2). The test demonstrated that the corner criteria could be satisfied.
For a BV/SS design, the edge of slab detail is important, not only to resist the required loads and accommodate expected differential deflections but also to minimize construction cost. There was a need to improve common details, which usually include slab embedded items that are often not properly located, tilted, and/or missing.
The edge of slab tolerances were defined; in-out (plus or minus ½ inch), up-down (plus ½ inch up and 1 inch down). The edge of slab tolerance is tighter than typical construction but was agreed upon as the innovation of the connection evolved. The up-down tolerance included the effects of the building frame creep and shrinkage.
Building floors were 9-inch-thick post-tensioned slabs. Edge forms for post-tensioning typically have round holes for tendons. Placing an embedded bolt in the slab, protruding through some of the holes to connect the brick ledger, would be easy. The bolt could be bent to engage the bottom of the slab form and a coupler added at the end to attach a bracket for a push-pull rod connection to the top of the floor below studs. This eliminated the need for the top of the stud system to have the questionable double-channel detail. The double channel detail is questionable because performance for both in-plane sliding and accommodating differential vertical movement requires careful installation.
The nominal 9 inches from the edge of the slab to the face of brick provided the opportunity for a custom ledger support bracket. Friction bolt connections were preferred over welding. Vertical slotted holes in the backup plate accommodated the vertical tolerance, and horizontal slotted holes in the ledger accommodated horizontal tolerance. Connections were typically spaced at 4 feet on-center, and the ledger angle was a 3×3×5⁄16 weighing 73 pounds for a 12-foot length (Figure 3).
The design of window and door lintels provided another opportunity for innovation. Typically, bricks above a door or window are supported on mild steel angles designed to a deflection limit of L/600. The angle is exposed to view and becomes an aesthetics issue. Also, there was the complexity of the doors and windows being inset 6 inches from the face of the brick.
Instead of the conventional steel lintel, a structural brick lintel was designed and specified. Figure 4 shows a unique pistol-shaped brick that was fabricated and reinforced with a stainless steel (SS) all-thread (much more economical than SS rebar). The lintel was shored for construction; a panelized lintel was not used due to project space restrictions and lifting limitations.
The above is only a part of the innovation applied to these two buildings. There is more, like the design of the thin stone façade at the base of the building and much more on other parts of the City Creek Center project as a whole, including the reinforced veneer (structural brick veneer) on the retail portion of the project.
The City Creek project demonstrates the value of performance-based-design and designing the curtainwall system in coordination with the rest of the design. For the two buildings, a total of 62 full-size curtainwall structural drawings were required. Costs were reduced and performance enhanced. Most important, the inevitable conflicts between parties involved in a complex curtainwall construction project were significantly reduced. The project became a successful team effort.
Curtainwall structural engineering fees, per square foot, are commensurate with structural engineering fees for the primary structure, but the technology and materials can be more challenging. The initial curtainwall design fees may likely be the reason owners do not take advantage of the overall cost savings, which is a lost opportunity.■
Some professional associations struggle to find social relevance, and optimally serve their membership. These difficulties are often the result of an inability or unwillingness to take action, the inclination to speak in silos, and the lack of aligned partners. Today’s unprecedented pace of technological, social, and generational disruption particularly challenges these organizations.
I strongly believe our structural engineering associations are outliers to this traditional approach. CASE, NCSEA, and SEI recognize the enormous opportunities associated with a unified vision, coupled with joint action. The 2019 Joint Vision for the Future of Structural Engineering was the first tangible result of this partnership. In this document, the three organizations envisioned a future in which structural engineers are widely recognized as vital contributors to the advancement of society. The ongoing collaboration demonstrates a commitment to using a uniform voice to implement change across our profession’s spectrum, from licensure to leadership training, from mentorship to messaging, from public perception to policy development.
Despite these efforts, our communities and our profession are suffering from the expanding COVID pandemic, the subsequent economic crisis, and the effects of long-term racial injustice. However, we have a choice in our response to these stressors. We can cling to past successes and manage the status quo, or we can embrace today’s disruption as an opportunity to create transformative change for our associations and our profession.
Structural engineers are recognized leaders in supporting our communities following natural and man-made disasters, such as earthquakes, hurricanes, and terrorist attacks. At this moment, we have an opportunity to embrace our record of proven leadership to provide support and action in response to longstanding racial injustice and inequity. As we survey our own demographic, it is starkly apparent that our structural engineering profession does not reflect the diversity of the communities we serve.
Last month, CASE, NCSEA, and SEI jointly issued a Call to Action to denounce racism and commit to furthering diversity, equity, and inclusion (DEI) in our organizations and the profession. While these powerful words represent a critical step to establishing a vision and a commitment to accountability, it is actions that lead to meaningful progress. With this fact in mind, NCSEA has publicly pledged to several actionable DEI goals. While our actions are currently in various stages of completion, NCSEA has made substantial progress with the following initiatives:Participation with SEI and CASE in the newly formed joint committee to improve professional equity and opportunity; Compilation and sharing of resources regarding racism, discrimination, and equity in the AEC industry; Preparation for unconscious bias training for all NCSEA leadership, including Board, Staff, and Committee Chairs; Planning for a program focused on racism, equity, and social justice in structural engineering; Collaboration with the NCSEA Structural Engineering Engagement and Equity (SE3) committee to report on additional dimensions of diversity, equity, and inclusion and evaluate new initiatives and programs; Partnering with the National Society of Black Engineers (NSBE) to identify and support mechanisms to increase the diversity and quantity of engineers entering the structural engineering profession.
Real change takes significant commitment, persistence, and intention. With this in mind, NCSEA developed an action plan that sets the framework for a long-term commitment to diversity, equity, and inclusion. We need your voice and active participation to advance diversity, equity, and inclusion initiatives and fight racial injustice. I firmly believe that our associations and the structural engineering profession are well-positioned to positively impact our communities and contribute to a better future for all.
The expansion of our professional and societal influence does not mean that our associations will cease traditional offerings, such as continuing education, professional networking, and licensure advancement. However, the structural engineering profession has historically struggled to achieve visibility, to influence public policy meaningfully, or to advocate for our profession. Embracing today’s challenges will result in new skills, audiences, and partners to not only advance diversity, equity, and inclusion in our profession but also improve our stature in the broader community.
As we strive for these more aspirational and impactful societal and professional goals, we realize that our voice must be loud, unified, and externally focused. More importantly, if we expect the public to listen when we speak about safer structures, improved public policy, or the value of our profession, we must also be willing to listen and respond to our communities’ discussions.
Whether developing public policy, delivering consistent advocacy, or supporting social change, the commitment to progress must be consistent and present at all levels. I call on you, my CASE, NCSEA, and SEI colleagues, to join me in bold, active, and collaborative actions to transform our profession and better serve our communities.■
Composite floor deck construction has become very popular. It combines structural efficiency with a speed of construction that offers an economical solution for a wide range of building types, including commercial, industrial, or residential buildings. Composite slabs consist of profiled steel decking with an in-situ reinforced concrete topping. The decking not only acts as a permanent formwork to the concrete but also provides sufficient shear bond with the concrete so that, when the concrete has cured, the two materials act together compositely to resist the loads on the deck.
Openings in composite floor decks are a common part of any building. These openings can range from small holes for pipes and conduits to larger openings for mechanical ductwork, storm drain pipes, or a group of small holes. These openings allow contractors to install relevant building systems such as heating, ventilation, and plumbing.
Openings can have a significant impact on the structural performance of decks. It is essential that all openings are examined by a professional engineer to determine their influence on the deck and whether reinforcement around the opening is needed.
This article provides an overview of the various methods of creating small and medium-sized penetrations and their impact on the structural performance of composite decks.
There are two main methods to create small and medium openings in composite floor decks: core-drilling holes and sleeving or boxing-out openings.
Concrete core drilling involves drilling rounded holes in concrete walls or floors (Figure 1). Diamond concrete-core drills are the most commonly used tools for this process. The core drill bit tends to consist of a steel tube with a matrix impregnated with diamond segments welded to the drilling end. The concrete coring bit is mounted on a rotating shaft of a concrete core-drilling machine and is secured to the wall or floor. A solid cylindrical concrete core or “slug” and metal deck under the cured concrete are removed from the hole once the drilling is complete. Due to the possible close spacing of existing floor slab reinforcement, reinforcement could likely be unintentionally cut during this process. Therefore, the location of the holes and the reinforcement should be coordinated with the structural engineer before coring. A scanner can be used to help locate the existing reinforcement steel to assist in avoiding it during the coring operation.
Sleeving or boxing-out is another approach to creating an opening. In this method, the opening is formed by setting sheet metal sleeves in the deck (Figure 2). Alternatively, there are some cast-in firestop systems, including firestop cast-in sleeves, that can improve and simplify the entire installation process and increase the productivity and efficiency of contractors. Check with your local regulations and project requirements on whether it is permissible to cut the deck. The Steel Deck Institute (SDI), Manual of Construction with Steel Deck (SDI-MOC3), provides some examples of decked over floor opening closures, as illustrated in Figure 3.
It is highly recommended to leave the steel deck intact until the concrete has cured. However, contractors may cut the opening through the steel deck before the concrete is poured; they see this as a more straightforward installation with less labor, allowing immediate access to the openings before the concrete is poured. However, cutting out the slab before the concrete is cured can prevent the deck from properly acting as a form. The steel deck must be examined by a professional engineer to determine if additional steel elements or temporary shoring are needed.
Composite floors consist of a concrete topping cast onto a metal deck. The topping can be light-weight or normal-weight concrete. The steel deck is a cold-formed corrugated steel sheet that spans between steel joists or beams and serves a dual purpose. It serves as a form during the construction phase while the concrete is poured and cured and serves as reinforcement to act compositely with the concrete to support the floor loads. Therefore, there are two main structural functions to be considered for the design of composite decks; (a) design the steel deck as a form to support construction loads, and (b) design the composite slab for superimposed floor loads after the concrete hardens. However, the design of the steel deck to serve as a form is usually more critical than the design of the composite floor to support superimposed floor loads. The steel deck profile and thickness need to be chosen such that the unshored span of the steel deck can support the construction loads.
As a formwork during concreting, the steel deck should be designed to resist anticipated construction loads. This design must meet the minimum design loads specified in the American National Standards Institute’s and the Steel Deck Institute’s Standard for Composite Steel Floor Deck-Slabs, ANSI/SDI C-2017. It also must evaluate three separate load combinations: (a) the dead weight of concrete and steel deck plus a 20 pound per square foot (psf) uniform construction live load, (b) the dead weight of concrete and steel deck plus a 150 pounds (lb.) concentrated load per foot width of the deck, and (c) the dead weight of steel deck plus not less than 50 pounds per square foot (psf) uniform construction live load. The engineer should also check the deflection of the deck at the construction stage to limit excessive deflections, which can lead to ponding of the concrete. Ponding can cause unintended dead load on the structure.
After the concrete is poured and cured, the deck acts compositely with the concrete to resist superimposed loads. Composite action is obtained by the shear bond between the concrete and the deck. The design of composite steel deck-slab systems reflects the engineering concepts used to design reinforced concrete beams. The concrete acts as the compression material and the steel deck bonded to the bottom of the concrete acts as the tension reinforcing steel. The bending capacity of the composite steel deck must be sufficient to resist out of plane gravity loads on the deck, which are typically superimposed dead and live loads in addition to the concrete and deck self-weight (Figure 4).
Composite decking is also used as a horizontal shear diaphragm to stabilize the building and to transfer in-plane shear loads (such as wind and seismic forces) to the building’s main frame lateral resistance system (Figure 5). For this purpose, the composite deck shear diaphragm is modeled as a horizontal beam with interconnected floor deck units that act as the beam web. Intermediate joists or beams function as web stiffeners, and the perimeter beams act as the beam flanges. A detailed design guide can be found in the Steel Deck Institute’s (SDI) Diaphragm Design Manual, Edition 4 (SDI-DDM04).
Due to the complexity of the design procedures of composite floor decks, deck manufacturers usually provide tables summarizing permissible loads, section properties, maximum unshored spans, superimposed loads, and diaphragm shear loads. However, these tables consider the deck as a solid uniform platform with no openings or penetrations. Since openings can impact the deck performance, the engineer must independently examine the penetrations and their effects on deflection, bending, and shear strength of the deck to determine if reinforcement for the deck is needed.
The size of openings in the deck may be categorized as small openings (up to 12 inches), medium openings (1 foot to 4 feet), and large openings (over 4 feet). Per the SDI Floor Deck Design Manual (FDDM), large openings should be designed to have all deck bearing edges supported by structural framing. Openings that are of medium or small size may be accommodated without structural frames. It is highly recommended that the deck not be removed from the opening before the concrete is cured. Additionally, non-compliance could lead to potential safety issues. Check with your local regulations and project requirements on whether it is permissible to cut the deck. Cutting the deck before the concrete is poured and cured reduces the flexural capacity of the deck and can induce excessive deflection. This can lead to concrete ponding during construction. An associated increase of the dead load on the deck may result from additional concrete poured to provide a level floor elevation. Also, cutting the web of the steel deck before the concrete is poured can reduce the steel deck’s vertical shear capacity locally around the opening and may result in deck web crippling under concentrated loads such as the weight of people or equipment on the deck during construction.
SDI-FDDM provides a method for the design of the small or medium openings in composite steel decks. In this method, the concrete above the top of the deck along the opening’s edges, perpendicular to the ribs, is assumed to act as a shallow beam, as illustrated in Figure 6. This beam can be designed as a reinforced beam or as a structural plain concrete beam to carry the sum of the dead weight of the deck-slab plus the superimposed design loads. The end reaction from this shallow beam must be supported as a point load on the composite deck-slab adjacent to the opening.
Note that closely-spaced openings may need to be treated as a medium or large opening. When the group of small or medium openings runs perpendicular to the span of the deck, the width of the hole should be considered to be the overall length along the string unless there is adequate deck remaining between the holes. However, when the groups of openings run parallel to the bearing direction of the deck, the width of the opening can be considered as the width of a single hole (Figure 7).
Openings and penetrations in composite slab decks are an unavoidable part of any structure to accommodate the installation of various mechanical, electrical, and plumbing systems. Typically, openings are created by core-drilling the concrete floor or setting sleeves to create an opening before concreting. Due to the potential safety issues in cutting the deck, check with your local regulations and project requirements before proceeding. Openings can reduce the structural capacity of the composite deck. To maintain the deck’s structural stability and strength during its service life, a qualified structural engineer should evaluate the openings and their impact on the structural performance of the slab/deck system and provide a reinforcement plan as required.
Per SDI-FDDM, large openings should be designed to have all deck bearing edges supported by structural framing. Small or medium penetrations may be accommodated without structural frames. Note that, for the design of small or medium openings, location and spacing of the openings should also be considered. A close grouping of penetrations transverse to the span direction of the decking should be treated as a single large opening.■
While many clients seek to pinpoint a singular cause for cracking of welds, it can rarely be attributed to one single mistake. Most often, a crack is produced in a “perfect storm” of errors made during the design, procurement, and execution phases of fabrication. Individually, these oversights would be unlikely to cause weld failures but, combined, they can cause disastrous results to any welding operation, even in reputable shops.
A large steel fabrication shop was assembling and welding built-up columns for a new high-rise building in Manhattan. During fabrication of one column, the shop’s quality control staff encountered visible cracking on the base metal of a welded joint. At the time of the discovery, welders were joining elements of 5½-foot-wide columns to be encased in concrete, which contained 3¼-inch-thick plates offset from the column’s web that would serve as connecting elements for the steel framing once encased. These embedded plates were joined to the column via 3-foot-wide, 3¼-inch-thick stiffeners extending from the web of the column to create a plate surface in the outside face of the future encasement of the column. The 3¼-inch plates were joined at perpendicular angles to each other by welded double bevel tee joints with back-gouging.
To confirm the extent and origin of the crack, magnetic particle testing (MT) of the welded joint and surrounding base metal was conducted by the shop’s quality control inspector. It revealed the crack shown in the photos, with yellow powder accumulating in the cracked metal to distinguish the extent of cracking. It is clear from the powder’s location that this fracture had originated in the heat affected zone (HAZ) at the weld’s termination and propagated as a transverse crack into the base metal. Ultrasonic testing revealed that the crack extended 1-inch-deep in the 3¼-inch-thick material.
This fabricator had diligently monitored welding parameters in accordance with a prequalified welding procedure specification (WPS). This WPS for Group II base metal required the use of a gas-shielded, semi-automatic flux cored arc welding (FCAW) process with 70 ksi wire. This is a process often favored by shops for both its productivity from a wire feeder as well as its penetration, attributed to its reverse polarity. The fabricator’s quality manager was able to provide valuable information such as wire diameter, shielding gas, preheat and interpass temperature, and post weld treatment (PWHT) details.
In this case, a preheat temperature of 225°F had been achieved. This is acceptable by AWS standards for Category B base and filler metal combinations in AWS D1.1:2015 Table 3.3. The FCAW wire was classified as H8, with less than 8 mL/100g of diffusible hydrogen. The double-sided tee joint had even been welded by alternating sides, a practice recommended by AWS to control thermal stresses during welding.
This prompted an investigation of the base metal by the fabricator, who assumed that since everything was prequalified and executed with good practice, there must have been some flaw in the base material. The fabricator had gone so far as to hire laboratories to perform limited chemical analysis of the steel, yielding no reliable results to indicate why the cracking had occurred.
Upon first inspection of mill test certificates of the steel received, it was evident that, while the WPS was perfectly acceptable for the designed ASTM A572 Grade 50 steel, it did not account for the properties of the steel that was actually received and being welded. In fact, the steel far surpassed the minimum yield and tensile strength specified for ASTM A572 Grade 50 steel, with yield values in the 62-63 ksi range and tensile values in the 91-93 ksi range. From a welding perspective, this steel would fall into Group III base metal, becoming undermatched by the 70 ksi filler metal being used to weld it. Undermatching of filler metal is favored where acceptable, such as in this case, where the design only demanded 50 ksi base metal. However, the extremely high tensile strength also pushed the base-filler metal combination into Category C, a category which requires a minimum preheat of 300 degrees F.
After determination of preheat via a hydrogen control method (Annex H of AWS D1.1:2015), it was verified that, indeed, this base metal should have been preheated to a minimum temperature somewhere between 300° and 320°F.
One can argue that the fabricator was entirely within its right to use AWS D1.1:2015 Table 3.3 and that the material was indeed certified as a Group II metal. However, whether or not this material can be classified as a different grade by ASTM or AWS is not the point. Instead, the mill test certificate’s information should have raised a flag that this material and and its required preheat needed special consideration beyond AWS’s general Table 3.3. This is confirmed in the AWS code’s commentary, which advocates against the use of Table 3.3 without careful consideration of factors as covered by Annex H used in the analysis. Simply stated, Table 3.3 is an available tool but it is up to the fabricator to determine if it satisfies the conditions required to make sound welds. In this case, elevated preheat beyond Table 3.3 would undoubtedly have been warranted. Annex H of AWS D1.1:2015 is an excellent tool for structural engineers tasked with reviewing mill certification reports since it aids in the determination of preheat using a combination of factors: chemistry, restraint level, and hydrogen control.
Despite its importance, insufficient preheat is rarely the sole cause of cracking. In this particular case, the weld was joining two very thick pieces of material, each 3¼-inch-thick. The volume of weld metal alone produces a joint of extremely high restraint, with stresses far exceeding the tensile strength of the steel during welding and cooling that occurred with each pass. The addition of stress relief holes at each end of the joint would provide a path for relief of heating and cooling stresses. Instead, the weld starts and stops abruptly at the ends of the tee joint, a perfect location for crack formation and subsequent propagation into the base metal.
Another noteworthy aspect of this operation was that the WPS did not have any provisions for post weld heat treatment (PWHT). AWS D1.1:2015 does not mandate the use of PWHT, but it does repeatedly emphasize that joints must be considered on an individual basis and, where needed, PWHT must be prescribed. In the case of steel over 2 inches in thickness, PWHT in the form of a controlled cooling rate would have been quite beneficial in relieving the stresses induced during welding.
Besides the measures previously discussed, other steps can be taken by production crews to improve the execution of this joint and prevent cracking. For example, utilization of H8 consumables places this gas-shielded FCAW process in a low-hydrogen category, which is a good start. However, current, voltage, and gas moisture contamination are variables of low-hydrogen demand projects that can be monitored and controlled to avoid increasing the amount of diffusible hydrogen in the joint.
In conclusion, finding a singular cause for weld cracking can be a challenging task, particularly in a shop with proficient welders and established welding procedures that are rarely questioned. Fortunately, control of at least some of the most common contributing factors can often be enough to preclude weld cracking. In this case, the contractor’s determination of appropriate preheat and interpass temperatures for thicknesses over 2 inches and providing stress relief holes in the joint would likely have been sufficient to prevent the welds from cracking.■
Photos courtesy of Atlantic Engineering Laboratories (AEL).
Structural engineers typically design standard connections that can be solved in several minutes using Design Guides, spreadsheets, or simple software. The non-standard connections are the real challenge. The 80/20 rule applies: 80% of the time is spent on 20% of connections. Non-standard connections are not only more challenging to design but also more costly and prone to errors. Finite element modeling comes to the rescue, allowing the calculation of complicated problems automatically. It has been used mostly for research purposes at universities or very large and costly projects. However, it is now becoming available for even small design firms to use on a daily basis. The desire for architecturally appealing and structurally complex solutions can lead to the use of novel, nonredundant systems with no prior record of proven performance. This makes safe, reliable engineering tools especially critical.
In connection design, the Component Method, where the connection is divided into simple discrete components and a basic model is constructed, has become a standard method for those designing with the Eurocode. Design rules are provided to determine the strength and stiffness of each component. AISC Design Guides for steel connections describe methods for particular joints, but the Component Method is more general and is implemented in most software for structural engineers. The components are designed by standardized analytical models, and internal forces are derived based on engineering practice. In current European research into steel connections, the design properties of components are refined or newly developed. The aim is to make the Component Method also available for conditions such as joints of composite steel-concrete structures or for, until now, non-standard connectors (e.g., hollo-bolts). Research into the deformation capacity of components is also being carried out, which is useful, especially for cyclic loading during an earthquake.
The design methods are still available only for the most common connection types. The Component Method model employs significant simplifications, containing only several springs with linear stiffness. The neutral axis is approximated for some loading cases, and the weakness of the method is revealed for a combination of loading, e.g., by biaxial bending moment.
An alternative is the use of finite element modeling, which is useful, especially for non-standard connections. The model is divided into simple small elements with defined properties by the process of meshing. The stress and strain in each element are determined by a numerical method. Two model types are recognized:Research-oriented finite element model (ROFEM) Design-oriented finite element model (DOFEM)
A standard approach for ROFEM is to perform an experiment and then create an advanced numerical model with fine meshing utilizing measured material properties and initial imperfections, often including residual stresses. The results of ROFEM should fit as closely as possible to the experimental results. By this process, a validated ROFEM is created, which may be used for further numerical experiments, in which the design material properties are often used. The influence of the main parameters is examined in a sensitivity study, where these parameters are varied and their effect on the load resistance is investigated. The creation of a validated ROFEM is very time consuming and costly, yet still cheaper and more feasible than experiments. ROFEM also provides further information that is difficult to obtain by experimental measurements.
The design-oriented finite element model uses design material properties (e.g., bilinear material curve with von Mises yield criterion instead of a true stress-strain material diagram) and standard safety factors. The DOFEM should ideally contain a significantly reduced number of finite elements and nodes compared to a ROFEM. The reduction in the number of elements and nodes significantly reduces computational effort. However, it must be proven by a mesh sensitivity study that the results are not affected significantly by this reduction. The DOFEM must be compared to either a validated ROFEM or traditional design methods – this process is called verification.
A special type of DOFEM is a model using the Component-based Finite Element Method (CBFEM). The method is a synthesis of the Component Method and the finite element method. The plates are modeled by shell elements and the components, e.g., bolts or welds, by nonlinear springs with their properties based on design codes and state-of-the-art research. CBFEM provides code checks of failure modes that are very difficult to capture by finite element analysis alone, such as crushing of concrete in compression or weld fracture. CBFEM removes the restrictions and most simplifications used in the Component Method. The neutral axis and forces in components for any type of load combination are determined by the finite element method.
Validation and verification ensure that the finite element analysis of the model is correct. The whole process is described in an example of a block shear of a bolt group.
The experiments by Huns et al. performed at the University of Alberta in 2002 are used for validation of a ROFEM created by Sekal in 2019 in ANSYS software (Figure 1). The tested gusset plates are 0.26 inches thick, the bolts have a diameter of ¾ inch, and the bolt holes are match drilled. Therefore, the bolts are directly in bearing. A true stress-strain material diagram is used. Only the thinnest plate predicted to fail is modeled. The model contains 190,264 hexahedron elements and needs around 26 hours of computational time on a dedicated server. The ROFEM model shows excellent agreement with the test results (Figure 2). (The model is considered validated, and it can be used for further parametric studies such as the effect of bolt pitch or edge distance on the block shear resistance.
A DOFEM using CBFEM is created based on the numerical experiments performed using the ROFEM validated on experiments. The models are compared to each other to prove the validity of CBFEM. This way, the effect of random imperfections of the specimens in experiments is removed. The DOFEM is further compared to several analytical models for block shear resistance of bolted connections. The models from AISC 360-10, CSA S16-09 (Canada), EN 1993-1-8:2005 (Eurocode), and prEN 1993-1-8: 2020 (Eurocode-draft) codes are investigated. Furthermore, the results of analytical models by Driver et al. (2005) and Topkaya et al. (2004) are presented.
The design-oriented CBFEM model uses shell elements with a rather coarse mesh. The finite element model is created in the background of the software and does not require a high level of expertise about the numerical method from the user. The mesh is predefined near bolt holes. Bolts are modeled as nonlinear springs which are connected to the nodes at the edge of the bolt holes by links with nonlinear load-displacement behavior. The bilinear material diagram with insignificant strain-hardening is used for plates. The slight slope of the plastic branch improves the convergence of the solver, and the impact on the precision of results is negligible. The limit resistance of a group of bolts in bearing is determined when the plastic strain at the plate reaches 5% (EN 1993-1-5: 2005). The bearing and hole tear-out resistances of each bolt are checked by formulas from the appropriate code. The computational time on a personal computer is in seconds.
The comparison is shown in Figure 3. All design models are conservative compared to this experiment and corresponding ROFEM. The results of the CBFEM model and ROFEM do not match each other perfectly because match drilled bolts were used in the experiments. The shear stiffness of a bolt in the CBFEM model is set to conform to the average behavior of a bolt in standard holes. The resistance of the CBFEM model is smaller due to the neglected strain-hardening of plates and small limit of plastic strain; the guaranteed strain at fracture of structural steel in tension must be at least 15% (Figure 4).
On the other hand, the coarse mesh leads to higher load resistances. The resistance of the CBFEM model nearly matches the resistance determined by AISC 360-10 and prEN 1993-1-8: 2020. It is conservative compared to the model by CSA S16-09 and, at the same time, unsafe compared to EN 1993-1-8: 2005. The current Eurocode analytical model is known to be too conservative and will be modified in the next generation published in the final draft of prEN 1993-1-8: 2020.
The design-oriented finite element model using CBFEM is extensively verified, and the studies are published. It is implemented in several commercial software, such as IDEA StatiCa or Hilti Profis. The results of finite element analysis are first compared to the traditional analytical design procedures in current codes. The aim is to differ from the analytical procedure by 10% at most. If CBFEM provides unconservative results, the model is also verified against ROFEM validated by experiments. Analytical models often contain several simplifications, e.g., rigid base plate assumption or linear interaction of bending moments around two axes perpendicular to each other. Finite element models are, from their underlying principle, much more precise.
Often, the structural engineer is required to make conservative assumptions and educated guesses when designing non-standard joints, which are not described in Design Guides. CBFEM is a tool able to calculate such estimates in minutes, and provide not only design load resistances but also a visual presentation of behavior and a risk of possible failure modes.■
Latour, M., Rizzano, G. A theoretical model for predicting the rotational capacity of steel base joints. Journal of Constructional Steel Research. 2013, 91, 89-99. DOI: 10.1016/j.jcsr.2013.08.009. ISSN 0143974X.
Gödrich, L., Wald, F., Kabeláč, J., Kuříková, M. Design finite element model of a bolted T-stub connection component. Journal of Constructional Steel Research. 2019, 157, 198-206. DOI: 10.1016/j.jcsr.2019.02.031. ISSN 0143974X
Wald, F. et al. Benchmark cases for advanced design of structural steel connections, Prague, Česká technika, 2019.
Sekal D. Analysis of Block Shear Failure, Diploma Theses, TU Munich and CTU in Prague, 2019.
Huns B. B. S., Grondin G. Y., Driver R. G., Block Shear Behaviour of Bolted Gusset Plates, Department of Civil and Environmental Engineering, University of Alberta, 2002
Robert G. Driver, Gilbert Y. Grondin, Geoffrey L. Kulak, Unified block shear equation for achieving consistent reliability, Journal of Constructional Steel Research, 2006, 62, 210–222.
Topkaya C., A finite element parametric study on block shear failure of steel tension members, Journal of Constructional Steel Research, Ankara, 2004
AISC 360-10: American National Standard – Specification for Structural Steel Buildings, American Institute of Steel Construction, Chicago, 2010
S16-09: Design of steel structures, CSA Group, Toronto, 2009.
EN 1993-1-8: 2005: Eurocode 3: Design of steel structures – Part 1-8: Design of joints, CEN, Brussels, 2006.
prEN 1993-1-8: 2020: Eurocode 3: Design of steel structures–Part 1-8: Design of joints, Final draft, CEN, Brussels, 2019
EN 1993-1-5: 2005: Eurocode 3: Design of steel structures – Part 1-5: Plated Structural Elements, CEN, Brussels, 2005.
IDEA StatiCa Connection: Theoretical background. Available at https://resources.ideastatica.com ANSYS®, Help System, ANSYS Parametric Design Language Guide, ANSYS, Inc.
Many of the advances we have seen in mass timber construction in recent years are due, in large part, to the availability of modern wood fasteners. The two most common types, self-tapping screws (STS) and glued-in rods (GiRods), will be discussed in this two-part series. Neither of these fastenings is directly addressed by the current U.S. National Design Specification for Wood Construction (NDS®) or the Canadian Standard for Engineering Design in Wood (CSA O86). These articles provide background and relevant design considerations to assist structural engineers in designing with these novel products.
Many large-format structural timber products have become popular in recent years. Further information on mass timber products can be found in STRUCTURE’s January 2017 article, Mass Timber: Knowing Your Options. The success of these new mass timber products is partly due to the availability of new, modern wood fasteners. Traditional bolts, lag screws, nails, wood screws, timber rivets, split rings, and shear plates have been the recognized tools by timber engineers for their reliable record of performance. For example, Teco (split ring) timber connectors were common in large-span heavy timber trusses and bridges during World War II, offering high load capacity. Unfortunately, these same connectors often require high skill and manual labor with specialized tools for installation. Modern mass timber construction fastenings, on the other hand, are quick and easy to install and uninstall and can be concealed for aesthetics and fire protection. Modern fasteners can also provide ductility and energy dissipation under earthquake or blast loads. Some examples of modern fastenings were covered previously in STRUCTURE’s August 2014 article, Modern Timber Connections – since then, long self-tapping screws have begun to dominate the mass timber world.
Wood screws and lag screws have been around for a long time and are often what comes to mind for threaded fasteners. The design criteria for wood screws and lag screws are clearly defined in the NDS and CSA O86, and fastener sizes and shapes are detailed in ANSI/ASME standards. Material properties for traditional wood screws are not specified; however, most lag screws, as specified in ASME B18.2.1, must conform to ASTM A307, Grade A for low carbon steel.
Wood screws and lag screws have proven track records. However, there are some drawbacks. For example, lag screws must be installed in pre-drilled holes, typically drilled in two steps for some sizes of screws with different diameter bits for the threaded and unthreaded parts of the shank. Lag screws can be challenging and slow to install using a wrench, because larger diameter lag screws may require high torque. Power drivers for lag screws are prone to overdriving, which can compromise withdrawal capacity and fixity. Traditional wood screws, in comparison, generally do not require pre-drilling, but are limited in size and capacity and can fail in torsion during installation.
This is where self-tapping screws enter the scene. High-performance structural screws were developed by researchers and manufacturers in Europe starting in the late 1990s. Now available from both European and North American manufacturers, these screws range in diameter from 5⁄32 inch (4 mm) to 9⁄16 inch (14 mm) with lengths up to and exceeding 3 feet (1 m). Although sometimes referred to as “self-drilling,” Self-tapping Screws is a more commonly used term.
A key feature of self-tapping screws is the material: special carbon steel with tensile strength up to 145 ksi (1000 MPa), significantly higher than the steel used for lag screws and wood screws. Another key feature is the screw geometry. Through extensive design and test programs, manufacturers have developed features such as thread shapes (for strength and ease of installation), the extent of threading (partially or fully threaded), head shape (for different applications), and drilling/tapping tips.
Many of the features, developed for ease and speed of installation, also have the added benefits of reducing wood splitting and eliminating the need for drilling pilot holes in many cases. The high strength steel also makes it possible to drive long screws under high torque without breaking the screw in torsion during installation. Many different head shapes are available for different connection configurations, such as wood-to-wood and steel-to-wood applications. Some heads have built-in washers to dramatically increase head-pull-through resistance, which is an essential property for partially threaded screws, as described below.
Although wood screws, lag screws, and self-tapping screws are all used to resist shear loads and/or withdrawal loads, self-tapping screws also possess the ability to transfer load in tension or compression from one end of the screw to the other when fully threaded. Fully threaded screws made from higher-strength steel change the type of failure mechanism generally associated with screws. As a result, fully threaded self-tapping screws can be used for new applications like reinforcement, as shown in Figure 1.
Fully threaded screws transfer load from one part of a wood member into another by the threads of the screw, making it possible to prevent wood splitting, perpendicular-to-grain crushing, and shear along the grain. Splitting and shear are brittle failure modes that often control the capacity of connections in wood. When splitting or shear failure is prevented, the overall connection capacity is increased until another failure mode is reached, but at a much higher load level. Figure 1 illustrates a variety of cases, including notches and bolt groups, both of which have high stress concentrations in shear and perpendicular-to-grain tension, respectively. Openings in large glued-laminated beams for ductwork or pipes can be reinforced using self-tapping screws. Another benefit of the fully threaded screws, in addition to high withdrawal capacity, is the elimination of head-pull-through failures because the thread transfers the load, not the bearing around the head. Other examples shown in Figure 1 are shear reinforcement of deep beams, radial tension reinforcement of arches and tapered glulam beams, and compression (bearing) reinforcement at supports.
Wood screws and lag screws are typically installed perpendicular to the face of wood members to transfer shear forces. Screws can also be loaded in withdrawal (i.e., tension). The withdrawal capacity of traditional fasteners is limited by the withdrawal resistance of wood and the tensile resistance of the fastener shank. Since the quality and the strength of traditional screws are usually unknown to the designer, the penetration length of the threaded portion greater than 10 times the diameter of the screw is not considered in the design to minimize the risk of tensile failure of the screw. This uncertainty is accounted for in Allowable Stress Design (ASD) using conservative reference values (1⁄5 and 1⁄6 of the mean values for lag screws and wood screws, respectively) and low resistance factors in Load and Resistance Factor Design (LRFD) and Limit State Design (LSD) (0.65 and 0.6 in the NDS and CSA O86, respectively). This significantly limits the effectiveness of traditional fasteners in modern mass timber structures.
Self-tapping screws, on the other hand, provide the unique benefit of withdrawal resistance approximately three times higher than their shear resistance, as shown in Figure 2. It is better to take advantage of the screw’s withdrawal capacity rather than its shear (lateral) capacity. The connection can still transfer the shear force, but an inclined screw, as shown in Figure 3, develops a much higher capacity. The angle of inclination, 30° to 60° to the grain in the loaded wood member, results in a combination of axial and shear forces in the screw. As shown in Figure 3, under shear loading, a single self-tapping screw installed at 45° to the grain can be equivalent to multiple screws installed conventionally, perpendicular to the face.
Another interesting behavior of axially loaded self-tapping screws is that the connection stiffness is nearly ten times higher than the stiffness under lateral loading, as shown in Figure 2. This stiffness advantage does come at a cost: brittle failure can occur if screws are overloaded in pure withdrawal, without visible warning, unlike ductile behavior. However, by inclining self-tapping screws, as shown in Figure 3, the designer can take advantage of the overstrength in axial resistance of the screw and may also benefit from plastic deformation through bending.
Fully threaded self-tapping screws are mostly used to connect mass timber panels in floor-to-floor, wall-to-wall, and floor-to-wall joints with and without steel hardware. A variety of connection configurations are shown in the recent edition of the CLT Handbook (free download at clt.fpinnovations.ca). Likewise, these screws can be used in glulam header-to-beam connections and for local reinforcement of members, as noted above. They can also be used for attaching lifting anchors for CLT panels, as shown in Figure 4, for loads in the range of 2.9 kips (13 kN).
Partially threaded self-tapping screws also can be used in a wide variety of applications with and without steel hardware to resist shear between two adjacent members. These screws can also be used to develop composite action between mass timber beams or panels and concrete, as shown in Figure 5. Other applications for partially threaded self-tapping screws include attaching insulation to mass timber members.
The NDS and CSA O86 do not currently address the design of connections with self-tapping screws. While codes and standards tend to lag behind product development and market demand, specific product approvals can be used in lieu of explicit code recognition. In Europe, designers rely on suppliers for their National Technical Assessment (NTA) and European Technical Assessment (ETA) reports for each screw and connector model – dozens have been tested and approved. Several of these screws are available in the North American market and some with production, service centers, and design guides for the U.S. and Canada. A few have ICC-ES or CCMC (Canadian equivalent to ICC-ES) approvals. It is best to ask screw manufacturers or suppliers for technical support and copies of their design guides. Pay attention to the following technical considerations:Quality control. The supplier must ensure proper manufacturing quality control (material quality) since connection capacity is highly reliant on the tensile strength of the screw. Fastener selection. Self-tapping screws have many features such as thread and shank diameter, full or partial threads, type of head and tip, material and coating, and more. The designer must choose the right screw for the application and consider the overall cost to the project as well as availability. Contractor requests for substitutions also require careful review. Design values. Conversion of European design values is required to determine ASD or LRFD design values (and LSD in Canada) to be compatible with building codes accounting for load-duration and other adjustment factors. Group effects must also be considered. Ask the supplier for guidance. Spacing. Determine spacing requirements parallel- and perpendicular-to-grain, including end and edge distances, screw lengths for thickness of the members, angle of inclination, and wood density. Tight spacing may induce brittle failure modes, such as splitting, row shear, block shear, or group tear out. Pre-drilling. Although self-tapping screws can be installed without pre-drilling, screws of larger diameters (3⁄8 inch or 10 mm and greater) may require pilot holes, especially in denser wood species and those prone to splitting (Douglas-fir, Hem-fir, and Western Red cedar). The manufacturer should provide the diameter and length of pilot holes. Pilot holes are recommended for installing long screws in compact joints and for reinforcement applications to ensure accurate installation. Insertion torsion. Suppliers limit installation torque to stay below the torsional capacity of the screws. Long, fully threaded screws should be inserted without interruptions. Corrosion. Self-tapping screws used in exterior applications should be stainless steel or have appropriate treatment such as electro- or hot-dip galvanization.
Trends to follow include self-tapping screws used for punching shear reinforcement in mass timber panels and new specialty connectors that combine prefabricated steel components with the screws. In life-cycle assessment analysis, screws can be backed off and allow for disassembly of structures for future re-use.
Self-tapping screws have a significant foothold in mass timber construction and will likely find their way into U.S. and Canadian building codes and standards soon.■
Round hollow structural sections (HSS) are used in a plethora of applications – from bridges to transmission towers and stadium roofs, or from handrails to posts. HSS are also used beyond structures. For example, HSS are used as sprinkler pipes, oil transmission lines, and pistons, which can make sourcing a confusing headache. This article assists in navigating it all from a structural engineer’s point of view.
Round hollow structural sections are not only aesthetically pleasing and a favorite for architectural design, but they are also efficient structural members. With their lack of a weak axis, they are superior in compression. Their closed shape makes them preferred when torsionally loaded. When designing connections to round HSS, there are fewer limit states to consider due to the geometric nature of the section. Round HSS can also be filled with concrete to increase compression capacity and provide fire resistance.
Currently, Steel Tube Institute (STI) producers dual-certify all of their products to ASTM A500 Grade B/C, meaning that the material meets the specification requirements for both A500 Grade B and Grade C. In 2017, the American Institute of Steel Construction’s (AISC )15th Edition Steel Construction Manual was released. In it, the capacity tables are calculated for A500 Grade C to reflect this as the predominant material in the marketplace. Therefore, the design community should design using Grade C, as that is being purchased and what has been provided for many years – not only for round sections but for all HSS.
Round sections should be specified as either A500 or A1085. Historically, the belief was that A53 was the most available round section and, therefore, the most cost-efficient. This is not the case. A53 is the standard specification for steel, black lacquer coated, welded, and seamless steel pipe. It is intended for use in mechanical and pressure applications as well as for use in ordinary steam, water, and air lines. ASTM A500 is the standard specification for cold-formed, welded, and seamless carbon steel structural tubing. Available in four grades, A through D, it is intended for use in construction and structural applications. Unlike A53 piping, which is only round, A500 is available in more shape options, most commonly round, square, and rectangular.
In addition to these differences in intended use between the two steel products, many additional details are critically important for engineers, especially as they relate directly to matters of cost and quality. Consider yield strength. No matter the grade, A500 material’s yield strength will be greater than A53 piping. Although A53 was, at one time, the standard specification for round shapes, specifying A53 for columns or braces of a building results in a thicker, larger section than if using the stronger A500. Structures designed with A500 require less steel by weight; the cost-saving implications are clear.
An A500 round also has a tighter outside diameter (O.D.) and wall tolerances. When using an A500 round for a building column, you could specify an HSS8.625×0.322 with an outside diameter tolerance of +/-0.75% and a wall tolerance of +/-10%. The A53 equivalent, an 8-inch standard pipe, has an O.D. tolerance of +/-1% and a wall tolerance of -12.5%. Another word to the wise: A53 pipe (Figure 1) is available only in lengths of 21 feet and 42 feet. A500 rounds can be produced in lengths from 20 feet to 75 feet.
When selecting section sizes for structural design, you can be assured of not only the desired cross-sectional dimensions but also the necessary straightness with A500, as producers must also adhere to a straightness tolerance specified in A500. With A53, there is no specification in the standard for how straight the pipe must be.
Thus far, this discussion has focused on the structural characteristics of A53 and A500, but what happens on the outside matters just as much. When an A53 pipe is specified, part of its material cost is for the sealant that producers use to coat the outside of the pipe. In order to weld to these pipes, a fabricator must remove the sealant, creating an unnecessary cost and extra step in the fabrication process. The bare surface of the A500 tube makes it easier to paint after fabrication is complete. Also, because A53 pipe is produced to carry pressurized steam, water, or gas, the manufacturer must hydrostatically test the product, ensuring that it can withstand pressure when in use. If A53 piping is used in structural applications, the product includes the cost of those tests that a structural application does not require.
Lastly, if previously designing handrails with the “1⁄3 stress increase,” using A500 Grade C permits the use of the same sections as when specifying A53 with the stress increase.
Round HSS can be specified in a wide variety of shapes. Discerning what shapes are readily available is a little trickier. You may have noticed that there are hundreds of round HSS sizes listed in the software and in manuals used for design, although not all sizes are produced domestically. Engineers frequently wonder why there are fewer options for A53 pipe than A500 rounds. A53 pipes are designated to a Nominal Pipe Size (NPS), referring to a “nominal” outside diameter (O.D.) in inches plus one of three scheduled wall thickness (standard, x-strong, and xx-strong). They are sized this way because A53 pipes, designed to carry pressurized steam, air, or water, must work with standardized fittings and valves. There is no such need with A500 tubes, which are designated with much more precision and, accordingly, more efficiency. With A500 rounds, the outside diameter and wall thickness, in inches, are carried to three decimal places.
A good rule of thumb is to specify an HSS member that is equivalent to the NPS sizes. These are listed in Table 1 with the corresponding callout for an HSS. If deviating from those listed, it is best to check the Steel Tube Institute’s (STI) Capability Tool (www.steeltubeinstitute.org) to see if the section specified is domestically produced and, therefore, commonly available. This can also be done for rectangular sections.
A frequent question deals with the availability of round HSS for handrails. Table 2 lists the sections commonly available in ASTM A500 Grade B/C for handrail construction.
A question often posed when sourcing smaller sections is if ASTM A513 can be substituted because “A500 is not available.” First, challenge the question of availability. Check the Capability Tool and contact STI for assistance. Second, the answer to the substitution request is, “it depends.” ASTM A513 is a mechanical tubing specification intended for applications where dimensional tolerances are critical, but the strength of the member is not paramount. ASTM A513 has no physical requirements (minimum yield, tensile, or elongation), and A513 material is often not provided with a Material Test Report (MTR) indicating these properties. Therefore, if a substitution is requested, it is essential first to perform coupon testing or review the product’s MTR to ensure that it meets the physical requirements assumed in your design.
As the construction market has grown over the last decade, it seems that the desire for larger pipe and tube sections continues to grow as well. The availability of these sections should be a concern when considering specifying them.
ASTM A500 and ASTM A1085 have limitations for sizes with peripheries less than or equal to 88 inches. Anything larger than a 28-inch O.D. round section cannot be specified as A500. However, rounds even that large are not produced to the A500 specification domestically. Currently, the largest A500 sections made in the U.S. are 20-inch O.D. It is worth noting that, by the end of 2021, there will be a new domestic mill producing sections up to 28-inch O.D. In addition to the periphery limits, A500 and A1085 also have limits on wall thickness. Currently, the maximum thickness of an A500/A1085 member is 0.875 inches. It is anticipated that this limit will be increased to 1 inch in time for the opening of the aforementioned new mill.
If a project requires members that exceed what is currently produced in A500 or A1085, there is piping produced for other industries that can be used in structural applications, with caution. Most commonly, products that meet specifications such as ASTM A252, used for pipe pile foundations, or API 5L, for the oil and gas industries, can be procured in diameters up to 80 inches.
From a structural engineer’s point of view, the following are some of the notable differences between API 5L and ASTM A500/ASTM A1085:API 5L products come in many grades, denoted by “X65” or “X70,” which refers to the yield strength (e.g., X65 has a yield strength of 65,300 psi). Although API 5L is produced in very large diameters, the thicknesses of domestically produced pipes are limited to 1 inch. Imported material, especially from Asia, is available with walls exceeding 1 inch in thickness, although the availability of such products is often challenging to nail down. As API 5L is intended for use as pipelines in the transport of petroleum and natural gas, the tolerances and finishes that are expected for building products do not apply. API 5L is similar to ASTM A53 in that they are both hydrostatically tested; however, API 5L material is of a much higher quality as it is expected to withstand higher pressures and much higher temperatures than A53 pipe. API 5L is not an approved material per AISC 360-16, Specification for Structural Steel Buildings, as specified in Section A3.1a. However, the Commentary to this section states: “Other materials may be suitable for specific applications, but the evaluation of those materials is the responsibility of the engineer specifying them.” It is the EOR’s responsibility to prove the material used conforms to an ASTM Specification specifically listed in AISC 360-16, Section A3. API 5L has two product specification levels, PSL 1 and PSL 2. PSL 1 provides a standard quality level for line pipe. PSL 2 includes additional requirements for chemical composition, fracture toughness, a maximum yield strength, and additional nondestructive testing. Today, the most common grade of API 5L pipe available for structural applications is Grade B or X42 (PSL 1); however, there are 40 other grades given in API 5L, many of which may be available. In an additional requirement, PSL 2 stipulates a yield-to-tensile-strength ratio of 0.93 maximum for Grade B and X42 up to X80. This is important, as some of the connection strengths given in Chapter K of AISC 360-16 are rooted in the ductility of the material that produces the anticipated connection deformation. The maximum yield-to-tensile ratio for the materials used in the development of AISC 360-16, Chapter K, is 0.80. If a large section is required, but the stringent chemical and testing requirements of the API 5L specification are not, it may be prudent to call out the section as “ASTM A500 Grade C or approved equivalent.” This allows a mill that has not gone through the rigorous certifications necessary to obtain an API license to produce the material needed for a construction application, which may save significant project costs.
ASTM A252, Standard Specification for Welded and Seamless Steel Pipe Piles, is a material specification for steel pipe piles for foundations where the steel either acts as the permanent load-carrying member or as the form for cast-in-place concrete piles. STI does not recommend the substitution of ASTM A252 for ASTM A500 unless extreme care is taken. A few items of note follow:ASTM A252 can be specified in one of three grades. Yield strengths vary from 30 to 45 ksi, and tensile strengths vary from 50 to 66 ksi. There are no chemical composition requirements in ASTM A252. Although A252 is frequently produced in large sections, the specification does not speak to the tolerance for sections exceeding 24 inches in diameter and/or 1⁄2-inch thickness. The tolerances in A252 are more lenient than A500 for wall thickness, and it has no tolerance for straightness. Similar to API 5L, ASTM A252 is not an approved material per AISC 360-16.
If A252 is substituted, the EOR should account for its thinner wall, the lower yield strength, and the variable chemistry that may affect the members’ weldability.
When considering the total cost of a structure, the fabrication is a significant portion of the steel package cost. The handling of the material during fabrication is a contributor to the overall fabrication cost; it should be noted that round HSS can be more challenging to handle in the shop as it tends to roll. Marking and adding pieces to quadrants at 90 degrees to each other on a round piece is not quite as easy as it is on a rectangular section. Additionally, when connecting a round section to another round section, like in the truss shown in Figure 2, the cut necessary to connect the branch member to the chord is complex. This fabrication step has been simplified with the implementation of lasers into fabrication shops. However, without lasers, it can be quite complicated. While round sections are often the most efficient per weight, it may be more cost-effective to use a square or rectangular section to aid in the fabrication costs.
The requirements for the chemical composition of the commonly specified structural steels and, in particular, the limiting values of carbon equivalents, have been selected to facilitate weldability. The American Welding Society’s AWS D1.1, Structural Welding – Steel, in Table 3.1, lists prequalified steel materials and grades that have been selected because they have historically displayed good weldability. ASTM A53, A500, A1085, and API 5L Grade B, X42, and X52 are all listed as approved base metals for prequalified welding procedure specifications (WPS). Steel grades not listed in Table 3.1 may be new and have simply not been incorporated into D1.1 or, as is the case for ASTM A252, have been excluded because their mechanical properties and chemical compositions are not sufficiently defined. For these materials to be used, a special qualification test is required.
ASTM A500 and A1085 round sections are produced with a straight seam weld, with the outside weld bead scarfed or cut smooth with the outside surface. Specifiers should be aware that other specifications for round sections, particularly large pipes, are also produced with a spiral weld (Figure 3). These weld seams wrap around the member rather than straight longitudinally down the member. This is of particular importance if the member is to be used as an element in architecturally exposed structural steel (AESS). In that case, it is likely necessary that the member should be specified on the contract documents that it shall be “straight-seam welded.”
All of the materials mentioned in this article have different tolerances innate to their specifications (Table 3). As noted above, it is vital to ensure the assumptions made about the material in the development of the code meet or exceed what is provided in the actual member proposed to be used. Additionally, there are other requirements, like straightness, that may be worth investigating if an alternate material is sourced for a project.
When designing with round HSS, if designers stay in the “wheelhouse” (get it?), with outside diameters ranging from 3.5 inches to 12.75 inches, stick to A500 Grade C. These are the most economical sections because they are the most readily available and demonstrate the most efficient use of the material. If the project demands going outside that range, keep this article handy or contact STI for assistance.■
A Díj odaítélésére írásbeli javaslat alapján kerül sor. Javaslatot bármely főépítész, önkormányzati és hivatali vezető, vagy bármely szakmai és önkormányzati szervezet, illetve szövetség tehet. A Díjra nem javasolható hivatalban lévő állami főépítész, továbbá olyan személy, aki az Alapító Okirat szerint részt vesz a Díj odaítélésének véleményezésében A konferenciát rendező település...
A szervezők szeretettel várják mindazok jelentkezését, akik megnyitják értékes, érdekes épületük kapuit a látogatók előtt (lehetőleg épületvezetéssel), vagy több épületet bemutató tematikus sétát szerveznek. Várják azokat a szakembereket is, akik vállalják, hogy bemutatják az érdeklődőknek a jelentősebb helyreállításokat, restaurálásokat, valamint azt, milyen folyamatok szükségesek az örökség megőrzéséhez, megújításához. Várják azok...
A felsőoktatási pótfelvételi eljárás során a Simonyi Károly Műszaki, Faanyagtudományi és Művészeti Karán, a 2020/2021-es tanévben induló költségtérítéses képzések közül két építészeti pótfelvételi is indul augusztus 9-i jelentkezési határidővel. Az Építész MSc mesterképzés célja építészmérnökök képzése elsősorban az építészeti tevékenységek - épülettervezés, építészeti környezetalakítás, településtervezés, műemlékvédelem, építés- kivitelezés és -szervezés,...
(HOUSTON – July 27, 2020) Stafford Municipal School District (SMSD), the only municipal school district in Texas, will open its new facilities for middle school and administration next month. The district has plans for a ribbon cutting event and virtual tours, but these are being adjusted due to the pandemic and to accommodate community participation.
The new facilities are being constructed as part of SMSD’s $62 million bond program that passed in November 2017. The bond program provided funds to address growth and expansion at SMSD, which enrolled approximately 3,600 students in the 2019-20 school year.
“We are thrilled with our new space. We can’t wait for staff, students and the community to see the final result and enjoy the renovations of our complex in person one day soon,” said SMSD Superintendent Dr. Robert Bostic.
The new $26 million middle school will accommodate 950 students in sixth, seventh and eighth grade. The three-story building, encompassing 139,360 square feet, includes 21st century classrooms, science laboratories, robotics, engineering and computer labs, band and two art rooms, fitness room, library, two gymnasiums and a cafetorium. The existing middle school was built in 1983 during the district’s inception.
The new two-story, 26,362-square-foot administrative building includes office areas, training and conferences rooms, and a board room for meetings. The $6.9 million facility includes a district memorabilia area where there will also be a 3D model of the complex installed. Both buildings were designed by AutoArch Architects and are being constructed by Drymalla Construction.
“The new facilities are aesthetically appealing and offer unique instructional opportunities for Stafford MSD students,” said JP Grom, vice president at Lockwood Andrews & Newnam, Inc. (LAN), the firm serving as the program manager for the bond program.
Other elements of the bond program include converting the existing middle school into a new Science, Technology, Engineering & Math (STEM) magnet school for grades 3-8 that will open in 2021-22 – the only one of its kind in Fort Bend County, a repurposed community center in place of the former administration building, a new outdoor educational plaza, converting the former intermediate school into an early childhood center, and renovation of the existing elementary and high schools.
LAN is a full-service consulting firm offering planning, engineering and program management services for the nation’s heavy civil infrastructure needs. With more than 350 employees across the United States, LAN is a national leader in the engineering industry and is consistently ranked among the “Top 100 A/E Firms” according to Engineering News-Record. LAN is a LEO A DALY company, an international architecture and engineering firm.
About STAFFORD MUNICIPAL SCHOOL DISTRICT
The mission of SMSD is for every student to graduate college and career ready without remediation. The district is extraordinarily diverse and serves approximately 3,600 students from preschool to 12th grade at six campuses — Elementary School, Middle School, High School and the College Career Center with new campuses for STEM, Middle School, and Early Childhood underway. In addition to outstanding students and excellent teachers, SMSD is extremely fortunate to have a high level of parental involvement in the schools and very strong partnerships with the city. Additional information about SMSD is available at www.staffordmsd.org.
The post Stafford MSD to Open New Middle School and Administrative Facility Next Month appeared first on Civil + Structural Engineer magazine.
A multifunkcionális csarnok koncertek, előadások, kiállítások megrendezése mellett helyet biztosít több sportág részére is. Kézilabda, kosárlabda, jégkorong, teremfoci, röplabda, tenisz, tollas, boksz, birkózás, lovas sportok, vívás, torna, küzdősportok, súlyemelés, egyéb tömegsportok hazai és nemzetközi versenyeinek is helyszíne lesz. A Kézilabda Szövetség elnöke, Kocsis Máté Facebook-oldalára tette fel a kézilabdacsarnok legújabb...
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Az elmúlt hetekben megtartottuk az első 3 hivatalos magyar GRAPHISOFT online tréningeket “Kreatív látványtervezés”, “Listázás és mennyiségkimutatás” és “Parametrikus tervezés – Grasshopper&ARCHICAD” témában. Nagyon jó tapasztalatszerzés volt és jó volt látni, hogy bár más a dinamikája mint az élő tréningnek, de ez is szuper hasznos és van létjogosultsága.
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The post Megtartottuk az első magyar online GRAPHISOFT tréningeket appeared first on Brick+Data.
ArchiCAD 24 delivers four years of under-the hood development to revolutionise model collaboration
Several high-profile AEC firms have written to Autodesk CEO, Andrew Anagnost, to voice concerns about Revit and getting value from subscription
Civil and environmental engineering experts Land & Water is pleased to announce that it has been awarded a contract to carry out essential maintenance works on the lakes at Blenheim.
With the lakes being fed by the River Glyme, Land & Water is currently undertaking essential works which involve the demolition and assessment of the Grand Cascade Apron which forms the lakes from the river. The work will allow Land & Water to create a new resin injection curtain wall, which is also currently the largest resin injection works undertaken in the UK to date.
A final step will include the construction of a new concrete apron and stone faced walls. This will help mitigate any further wash over and across the length of the apron works, in addition to the replacement of an existing wave wall which will ensure the protection of the pool which was built over 300 years ago.
The works are part of the large restoration projects taking place at Blenheim Palace that aims to future-proof the grounds of the World Heritage site. Land & Water is extremely proud to be supporting these works and ensuring that the iconic landscape created by one of England’s most renowned landscape designers, Capability Brown, is preserved.
Discussing the project, Blenheim Estates Director Roy Cox says: “Whilst for obvious reasons we have delayed the main dredge for a year, we have been able to start work with Land & Water to go ahead with the essential repairs to the cascade at the bottom of our lakes. The craftmanship employed by Capability Brown nearly 300 years ago is remarkable and it’s a credit to them that we are only now following in their footsteps to make sure we can preserve such important landscapes at Blenheim.”
Meanwhile, Kevin Kirkland, Construction Director at Land & Water, says: “We are extremely proud to be working on this prestigious project and look forward to working alongside the team at Blenheim. We have ensured that our team are aware of all safe practices on site during the current health pandemic and will continue to ensure that our client’s needs are met whilst following Government guidelines.”
This prestigious project, starting with the apron works and culminating in one of the largest inland dredges, will protect Blenheim Palace’s grounds for decades to come, maintaining the estate’s wonderful, historic lake. Works will continue as restrictions ease and all health and safety recommendations will be carefully followed.
Texas Landscape Creations utilized Caldwell’s 6,000-lb. capacity adjustable lifting grab to lift 3,000-lb. concrete blocks during a recent landscaping project.
The lifting grab was used over a three-week period with a SkyTrak telehandler (from Sunbelt Rentals) as the full-service landscaper installed a layer of 5 ft. by 2 ft. by 2 ft. blocks in the grounds of what will be a place of worship. In this instance, the end user honored a landscape and irrigation contract that covered installation of plants, trees, grass, retaining walls and the quarry blocks.
The grab, which is ideal for blocks of concrete, stone, rough marble, granite, or any other solid material, can handle loads as narrow as 3 in. and as wide as 60 in.—and everything in between. Custom configurations are available upon request. Here, it was utilized to move the concrete from the on-site parking lot, across a creek, to their eventual location.
Jeff David, owner / manager at Texas Landscape Creations, said: “We will definitely use it on future work. It is a very efficient product and its adjustable nature was of benefit to this installation, as it will be on other sites. We even changed the orientation of one handle to suit our requirements, which enhanced user friendliness even further. It also proved to be a real time-saver; I would guess that we saved 30% of the total time estimated for that project by using the new clamp.”
The Caldwell Group Inc., of Rockford, Illinois, design and manufacture the product to ASME B30.20 and BTH-1, design category B, service class 3 standards. It is suitable for high duty cycle environments and a color-coded decal indicates to the user the amount of travel remaining during each adjustment. Extended handles keep the operator away from the load, while the lifting eye allows for easy hook attachment, self-centers rigging, and will accommodate a fork, as was utilized on the church project.
David said: “Safety is our number one goal and as of now this is the safest way to install such blocks. Previously, we would have used forks and / or slings—usually a combination of the two.”
Texas Landscape Creations will continue to use the adjustable lifting grab for upcoming projects. David explained that the company is typically hired for commercial installations at office buildings and apartment complexes; homeowner’s association (HOA) entrances; and roadways. It has also been involved in projects on the campus of Texas A&M University. However, it retains a crew for smaller, residential work and has three mowing teams and two irrigation repair technicians.
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