| mérnökvagyok.hu
2020.10.21 11:08
Koppenhágában a hulladékégető merész terve valósággá vált: az Amager Resource Center többféle síelési lehetőséget kínál a körülbelül 16 ezer m²-es tetőterületen túrautakat a kirándulóknak és lépcsőket azoknak, akik gyalog másznak fel a Copenhill-re.

Az új koppenhágai hulladékégető üzem számára a központhoz közel találtak helyet, Amager szigetén, a régi északi kikötőben, ahonnan mintegy 100 ezer háztartást látnak el villamos energiával és hővel. A Bjarke Ingels Group vizionárius építészei az Amager Resource Center-t többcélú szabadidős létesítményként képzelték el, pozitívvá varázsolva a hulladékégető üzem imidzsét. Tekintettel az épület csaknem 90 méteres magasságára, a 60 méter széles és 200 méter hosszú épületen átnyúló sípálya ötlete valósult meg. A 450 méteres lejtő – amelynek egyaránt vannak meredek és sík szakaszai – egész évben használható, kezdőknek és profiknak egyaránt ajánlott, száguldjanak síléceken vagy snowboardon. Ez a tetőre épített száraz lejtő egyedülálló a világon.

Az erózióvédelem miatt a bitumennel lezárt és 30°-ig döntött beton tetőfelületbe ferde küszöböket építettek, amelyek a vizet az oldalsó elvezetőkbe terelik. Ezenkívül csavarhorgonyok segítségével számos oszlopot is bebetonoztak, gondolva a későbbi növénytelepítésre; ezekhez rögzítik majd a gyökeres földlabdákat. 3000 m²-es területen az erdei tájat idézik meg, legalább 300 fával. Az alapot az ABS műanyag jelenti, amelyek az alsó oldalukra laminált védő gumiszőnyegnek köszönhetően csúszásállóak. Erre jönnek a szűrők és 5000 tonna földréteg 20-100 cm vastagságban. Az ültetésnél Dániára jellemző növényfajokat választottak ki. A facsoport alatti nagyon meredek és erózióra hajlamos területeken úgynevezett vegetációs szőnyegeket használtak.

A 8000 m²-es sípálya alapját vízelvezető panelek képezik. Erre jön az aljzatréteg, két műanyag hálórétegbe ágyazva, és amelyeket félmillió kábelkötegelővel kapcsoltak szorosan össze. Körülbelül 70 000 fémlemezt is beépítettek, amelyekre rácsavarozták a 30 x 30 cm-es műanyag martaclapokat. Ez a tényleges lejtőfelület. A szőnyegek színe a világostól a sötétzöldig terjed, és a különböző lejtésszögek miatt az egész „hegyoldal” természetesnek hat, amelyen még a valódi fű is átnő. Természetesen a három tányéros lift és a három mozgójárda is igazi. Alternatív megoldásként lift is rendelkezésre áll, hogy egyetlen gombnyomásra a 90 méteres magasságban megépült kilátóhoz és a kávézóhoz repítse a látogatókat.

A sípálya mindkét oldalán körülbelül 3000 m²-es felületet alakítottak ki lépcsőkkel és többszörösen ívelt pályaszakaszokkal a túrázók igényeihez igazodva. Ezen a részen vulkanizált gumiból készült, rendkívül nagy teherbírású vízelvezető és épületvédő matracréteget telepítettek.

Az Amager Resource Center hulladékégető tetőkialakítása futurisztikus módon ötvözi a technológiát, az ökológiát és a sportot. Az a nagyra törő ötlet, amely szerint a hulladékégetőt sikerrel integrálják a városba, Koppenhágában sikeres lett, hozzáadott értéket teremtett és egyben úttörő példaképül szolgál.

*Forrás: *

**


| Tervlap
2020.10.20 17:07

Indokolttá vált a váltás egy mai igényeknek megfelelő, méretes, új stadionra. Az 1990-es évektől az egykor virágzó kikötővárosban az Albert Dock területén egyre-másra nyíltak a kiállítások, így a Tate Liverpool is. A rozsdaövezetként nyílvántartott, kihasználatlan dokkok revitalizálása beindult. Ennek hatására Dan Meis építész a Royal King’s Dockra képzelte el az...


| mérnökvagyok.hu
2020.10.19 18:07
A Cobe és a Dissing+Weitling irodák közös tervezésében jött létre Dánia új futurisztikus gyalogoshídja, mely a Køge Nord állomást köti össze két vasútvonal és egy nyolcsávos autópálya keresztezése felett. A nemrég átadott műtárgy kivitelezésében egy magyar mérnökcég, a Baumetall Design Kft. is komoly szerepet vállalt.

A két stúdió kígyószerű gyalogos hidat álmodott meg a vasútállomást használók komfortjának növeléséhez, amely két fontos vonalat – egy nagysebességű és egy elővárosi vasútvonalat – köt össze, és Dánia legforgalmasabb autópályája felett fut. A Koppenhágából érkező gyorsvonat naponta mintegy 8000 utast szállít, így különösen fontos a fenntartható fejlődés, illetve a környezetbarát közlekedés szempontjából.

A projekt lehetővé teszi az ingázók számára, hogy leparkolják autóikat, és nagysebességű vonattal juthassanak el a 35 km-re található Koppenhágába.

„Mivel az állomás naponta több mint 100 ezer autós és utas számára látható, ikonikus tulajdonságokkal kell rendelkeznie, egyszerűnek, mégis emlékezetesnek kell lennie úgy, hogy mindeközben jól illeszkedik a tájba” – mondta Steen Trojaborg, a Dissing + Weitling ügyvezető igazgatója a Dezeennek.

A tervezők céljai között szerepelt, hogy kellemes és vonzó környezetet teremtsenek az állomást használók számára. Az előtereket és a park-and-ride létesítményeket úgy tervezték, hogy megőrizzék a környezet harmóniáját, még akkor is, ha a jövőben városfejlesztésre kerül sor. Öt lifttel és lépcsővel lehet megközelíteni a 225 méter hosszú gyalogoshídat, amelyek mindegyike kiemelkedik a finoman hajlított, alumíniummal bevont hengerből. Hatalmas panorámás ablakok keretezik a kilátást a híd mindkét végén, míg a homlokzatok napernyőként szolgálnak.

A híd betonból és alumíniumból készül, szerkezeti acélelemekkel. Belül tölgyfa burkolatot választottak a tervezők, hogy lágyabb, melegebb, kellemesebb érzetet nyújtson az építmény. „Figyelemmel és tisztelettel, emberközpontú nézőpontból megközelítve a közinfrastruktúra és az ehhez kapcsolódó közterek kialakítása nagy hatással lehet sok ember életére. Rendkívüli mindennapi terek létrehozására törekszünk” – nyilatkozták a tervezők.

Forrás:

Skandináv áthidalások

Dr. Toldy Gábor (Baumetall Design Kft.)

A skandináv design már sok 10 éve világhírű és előremutató. Legyen szó Lego-ról, vagy az Ikea-ról, nemzetközi szinten a siker egyik záloga az, ha skandináv (dán, norvég, svéd) a designer. Eszköz, autó, tárgy vagy akár épület, a skandinávok mernek olyan dolgokat megálmodni, amelyek tágítják a mérnöki gondolkodás határait, felrázzák az elkényelmesedett mérnököket és fordítanak egyet a megszokottnak vett mérnöki gondolkodáson. Jó marketing, stabil környezet, fizetőképes kereslet, kísérletező készség, elfogadás ezek az alkotó és megvalósító erői a skandináv designnak. Az elmúlt 3 évben volt szerencsénk határozott részt vállalni két olyan mérnöki tárgy megvalósításában, amely egy külső szemlélő számára akár egyszerű is tűnhet, de a homlokzat mögé tekintve komplex mérnöki gondolkodás és tudás volt szükséges a megvalósításhoz.

A Køge Dánia legforgalmasabb vasúti vonalának bővítéséhez csatlakozó beruházás. A híd, amely 10 autópálya sávon és Dánia elővárosi vonalát és legfontosabb fővárosba közlekedő vasútpályáját köti össze. Ez a vasútvonal nem csak Dánia, hanem Svédország és az Európai Unió számára is kulcsfontosságú, mivel a világhíres Oresund alagút és hídrendszerrel köti össze Dániát Svédországgal, lehetővé téve megépülése óta a direkt közúti és vasúti kapcsolatot. Már önmagában az utal a híd hosszára, hogy milyen széllességű autópályát kell áthidalnia, a 225m hosszúság azonban nem rövid. A két vasútvonalat köti össze, Køge városával. Az elővárosi vonal, a déli és keleti irányba közlekedő távolsági és a nemzetközi vonalak között teremt kapcsolatot. Koppenhága gyors fejlődése, a jellemző fővárosiasodás, az egyre növekvő ingatlan árak miatt, nem csak a tömegközlekedés hatékonyság növelésében játszik kulcs szerepet a beruházás, hanem új ingaltan területek a városi szövetbe való integrálódását is segíti. Az elipszoid keresztmetszet és az arra kerülő Rib-Roof burkolat nem lenne érdemes Mérnök Újság cikkre, mivel azonban az épület nem egyenes, hanem magassági és alaprajzi eltérés is van benne, ez már alábecsült, jelentős kihívások elé állította az eredeti tervezőt. Magasságilag 3 méter, alaprajzilag 15m elhúzás van benne. Ez éppen elég ahhoz, hogy az ellipszoid csövön kétszer görbült felületek alakuljanak ki. Ezen felületek szerkezeti megoldásait, rétegrendjeit eredetileg nem gondolták végig kellőképpen. A már korábban írt cikkekben jeleztem ezzel kapcsolatos meglátásomat, miszerint a projekt korai fázisában szükséges olyan szakértőt bevonni, aki ezen problémákat előrelátja és még a tervezőasztalon megoldja azokat.

A hídszerkezet legfőbb statikai szerkezete a platform, amelyet 6 szegmensre osztottak és asszimmetrikusan pillérekre helyeztek. Az alsó platform részre kerültek rögzítésre a gerenda tartók, amely a zár burkolatot hivatott tartani. Sajnálatosan a rétegrend vastagságot alul tervezték a dán kollégák, emiatt a projektbe érkezésünk után módosítani kellett a vastagságot, ellenkező esetben a forma nem alakult volna ki megfelelően, abban törés lett volna látható. A 6 darab híd elemet a helyszín 2 oldalán szerelték össze, ahol a homlokzati rétegrend előszerelése is végezhető volt. A burkolat 4 részre osztódott, amelyre az ellipszoid forma miatt vált szükségessé. 1 üveg homlokzati rész, amelyet a Baumetall Design Kft. az Orosháza Glass-tól rendelt meg. A további 3 rész homlokzati részt az északi oldali víz elvezető csatorna és az épület alján meghagyott, cseppentő sáv adott ki. Az ablak alatti vízelvezető csatornába integrált ablak tartó bakok szintén nem szokványos megoldás, de erre lehetőséget adott az a tény, hogy bár az épület maga zártnak tűnik, az nem fűtött, inkább csak és eső védett. A szegmensek előszerelése után, 2-3 darab párhuzamos munkájára volt szükség az egységek beemeléséhez, amely igen látványos munkafolyamat volt. A beemelések után lehetett elvégezni a burkolatok véglegesítését és a pillér szerkezetekhez való zárását.



| MMK
2020.10.16 17:07

A Magyar Mérnöki Kamara Elnöksége 2020. október 14-i ülésén a szeptemberi küldöttgyűlés döntéseinek végrehajtásáról és a Választmány október 30-ra tervezett ülésének előkészítéséről tárgyalt. Kiemelt téma volt a mérnöki díjszabás aktualizálása is.


| mérnökvagyok.hu
2020.10.15 17:07
Egy debreceni családi ház, a budapesti Metrodom-Panoráma lakópark, valamint a szentendrei Ferences Gimnázium új épületszárnya nyerte a Wienerberger által kiírt, 2020. évi Építészeti Nívódíjat. Három kategóriában: új építésű ingatlanok, innovatív projektek és rekonstrukciós kategóriában keresték a legjobb épületeket.

Új építésű ingatlanok, innovatív projektek és rekonstrukciós épületek kategóriákban választották meg 2020 Építészeti Nívódíjas épületeit a Wienerberger által kiírt pályázaton. A kiírás szerint 2016 és 2019 között átadott épületek vehettek részt a megmérettetésen. Az elismeréseket október 15-én, Budapesten adták át a győzteseknek.

Az újépítésű ingatlanok kategóriában a mátészalkai Nagy Béla által tervezett debreceni családi ház kapta az elismerést. Az ingatlan kapcsán a zsűri az egyszerűséget és a funkcionalitást emelte ki, a tökéletes területhasználat mellett hangsúlyozták a projekt során megvalósult erős ökonomikus szemléletet.

Az innovációs díjat a budapesti Metrodom-Panoráma lakópark (képünkön) érdemelte ki, a Hajnal Építésziroda tervezésében. A bírálóbizottság kiemelte, hogy a lakópark ikonikus zöld homlokzatával vonzza a tekintetet, míg műszaki, szakmai megoldásával olyan minőségi szintet képvisel, ami kiemelkedő és méltó példája lehet a jövő épületeinek.

A Szentendrén található Ferences Gimnázium már 1950 óta működik a városban, az épület azonban egy ideje nem tudta megfelelően kiszolgálni a megnövekedett igényeket. Éppen ezért szükség volt egy új épületszárny kialakítására. A Golda János, Híves Melinda, Mészáros Erzsébet által megálmodott épületegyüttes így két belső udvar köré szerveződik. Az új, korszerű épületrész, amely többek között rendházi lakásokat, közösségi és kiszolgáló helyiségeket foglal magába olyan magas szinten valósult meg, hogy a rekonstrukciós díj kategóriájában első díjjal jutalmazta a zsűri.

A három kategória első helyezettjei mellett a zsűri még három okleveles elismerést is kiosztott. Ezeket egy szentendrei lakóépület (Bársony István tervezésében), a pécsi református iskola (Kokas és Társa Tervező Kft. tervezésében) és a kaposvári informatikai képzőközpont (Arker Stúdió Építészeti és Kereskedelmi Kft. tervezésében) megálmodói vehették át.


| MMK
2020.10.15 17:07

Egyhangú szavazást követően október 9-én a mérnökszervezetek európai szövetségének tagjává választották a Magyar Mérnöki Kamarát.




| Consteel Blog
2020.10.13 18:07

In this brief tutorial, we will look at the two main ways of defining sections in Pangolin for your structural model.

  • Loading them from a predefined section bank

  • Pangolin provides 7000+ predefined sections collected in the section bank, these include standard profiles like IPE and HEA from various continental regions (Europe, American (imperial), American, British, Chinese, Continental Steel, Russian) and also some manufacturers like Lindab, SBE, Brausa and so on.

    First, we have to filter out the section we are interested from the bank so as to avoid loading all 7000+ of them and bogging Grasshopper down.

    Here I use the Section Bank Previews component, which outputs a list of “Section Previews” based on the provided filters from the bank (as seen in the rightmost text box). After we are satisfied with the filtering, we have to actually load in the sections by providing the preview and material to the Section From Bank component as seen below:

    2. Defining them with parametric section macros

    We can also define custom sections with a slew of parametric section macros. For this, first place the Macro Section component, then choose which kind of section you wish to create using the Select Macro button on the placed component (eg.: hot rolled I profile, welded maltese cross, cold-formed sigma and so on).

    After this, we have to specify the name of the new custom section, its material. Finally, specify any parameters that you wish to change like the height or web thickness of the section. You can preview the defined custom section in the Rhino Viewport to get an idea about the section your parameters resulted in.

    For cold-formed sections, Pangolin and Consteel provide the unique ability to accurately model and calculate custom intermediate and edge stiffeners. For these cases, you have to first define the stiffeners using the Intermediate Stiffener and Edge Stiffener components with their own parameters then connect these stiffeners into the Macro Section components corresponding input parameters like below:

    Deconstructing Sections

    Finally note that these objects are not just the surface denoting the cross-section, but complex objects containing design parameters for Consteel as well as other information. You can access some of these extra attributes using the Deconstruct Section component.

    You can use this to for example parametrize the eccentricity between beams based on their sections' geometry. In the below example, I deconstruct a section, pull its outline into the deconstruct box component (where it gets converted into a bounding box before deconstruction) and use the Y domain of this box to get the actual height of the current section. This unlike just using the macro’s input height also takes into account possible additional height gained by a protruding stiffener.

    You can download the example file here.


    | mérnökvagyok.hu
    2020.10.13 18:07
    A NIF Zrt. beruházásában 2018 tavaszán kezdődtek meg az M8-as autóút Körmend-Rábafüzes közötti, 2×1 sávos, 28,9 km-es szakaszának munkálatai. A szakasz teljes hosszán zajlik a kivitelezés, azonban egyes szakaszok műszaki készültsége eltérő, bizonyos szakaszokon a beton burkolat alap készül, más helyszíneken már az aszfalt kötőréteg is elkészült.

    A projekt két szakaszra bontva valósul meg. A Körmend-Vasszentmihály közötti szakasz várhatóan 2021 augusztusára készül el, míg a Vasszentmihálytól Rábafüzesig tartó 9,45 kilométeres szakaszt már jövő áprilisban forgalomba helyezik. A kivitelezési munkákat az idei évben nehezítette a térséget érintő csapadékos időjárás és a Rába árterülete miatti folyamatos magas talajvíz.

    A szakaszon épül Magyarország egyik leghosszabb völgyhídja, az 575 méteres vasszentmihályi völgyhíd. A jelenleg zajló hídfejlesztések közül az egyik legnagyobbak számító műtárgyon az alépítmény már elkészült, az acél főtartók is a helyükön vannak, jelenleg a vasbeton pályalemez építése zajlik. A 11 támaszú völgyhídnak 22 méteres pillérei is lesznek annak érdekében, hogy átívelje a Vörös-patak völgyét, illetve a Nemesmedves-Vasszentmihály közötti utat.

    Körmend és Rábafüzes között négy különszintű csomópont (Körmend nyugat, Csákánydoroszló, Vasszentmihály, Szentgotthárd), egy szintbeni csomópont (86. sz. főút, kezdő csomópont), egy pár egyszerű pihenő (Gasztony) és egy pár komplex pihenő (Szentgotthárd) létesül.

    A teljes szakaszon 22 felüljáró, 13 aluljáró, 8,6 km útkorrekció, 5,1 km szervizút, 700 m kerékpárút (Körmend Nyugati csomópontnál) és 1,2 km zajárnyékoló fal (Körmend-Horvátnádalja térségében) épül.

    A projekt során 10,2 hektár csereerdőt telepítenek, 336 175 db fát, cserjét ültetnek, s több mint 2 millió m3 töltésanyagot kellett beépítenie a kivitelezőnek.

    (Forrás: NIF)


    | Tervlap
    2020.10.13 15:07

    A beruházás közel 300 milliárd forintba kerül. Ebbe az összegbe beletartozik az orvostechnikai műszerpark beszerzése is, de a közlekedésfejlesztési infrastruktúra kialakítása már nem. Az összesen 1 200 férőhelyes, kizárólag egyágyas szobákkal és a legkorszerűbb technológiákkal felszerelt intézmény természetesen integrálódik majd a hazai közellátásba. A tervezői koncepció törekvése szerint jól áttekinthető...


    |
    2020.10.13 11:11
    • A perspektíva-beállító ablak is megjegyzi a pozicióját
    • Import/export javítások (SAF modul)
    • TEKLA Structures vasalás export javítása bekapcsolt részletek esetén (TI modul)
    • Spirálkengyeles oszlop csavarási ellenőrzés javítás (RC2 modul)
    • Vasbeton gerendaméretező ablakban nem lehetett a támaszokat módosítani, ha az automatikus felismerés alapján ezek egymásba nyúltak (RC2 modul)
    • Átszúródás vizsgálatnál körönkénti vasalásnál is dokumentálja u_out értékét valamint az a_out és n_sr számítását (RC3 modul) • Acélméretezőben C szelvénynél Zsuravszkij képlet javítása (SD1 modul)
    • EC(PL) Téglafal méretezőben fal nyomószilárdság csökkentés a falkeresztmetszet függvényében (MD1 modul)
    • Az SC1 modul újdonsága: 4 oszlopba rendezett csavarokkal szerelt véglemezes kapcsolatok ellenőrzése
    • Az SC1 modul újdonsága: véglemezes oszlop-gerenda kapcsolatban az oszlop gerinclemezzel is megerősíthető

    | STRUCTURE magazine
    2020.10.13 08:22

    Available to download for free

    The American Society of Civil Engineers (ASCE) Structural Engineering Institute (SEI) has published Performance-Based Structural Fire Design: Exemplar Designs of Four Regionally Diverse Buildings using ASCE 7-16, Appendix E. This guidance, available free-of-charge to download, presents guidance for proper execution and potential benefits of structural fire protection.

    SEI received a research grant from the Charles Pankow Foundation for $230,000 to develop and publish the state-of-the-art exemplar procedural guidance to properly execute a performance-based structural fire design (PBSFD) complying with the nationally adopted standard Minimum Design Loads and Associated Criteria for Buildings and Other Structures, ASCE 7-16, Appendix E Performance Based Design Procedures for Fire Effects on Structures, with guidance contained in Structural Fire Engineering, Manual of Practice 138.

    Performance-Based Structural Fire Design includes the analysis of four regionally diverse, protected, steel-framed building designs by design teams from four leading structural engineering firms: Simpson Gumpertz & Heger (SGH), Magnusson Klemencic Associates (MKA), Thornton Tomasetti (TT) and Walter P Moore (WPM). The design teams worked closely with a panel of academic advisors from four institutions: University at Buffalo, Oregon State University, Johns Hopkins University and University College London (previously with University of Maryland).

    Part I includes an overview of the methodology, a description of the project’s design procedures, and summaries of each design team’s analyses, results and conclusions. Part II includes four design team reports that further document and detail the evaluation of the design scenarios.

    These exemplar designs demonstrate the most significant benefit of PBSFD, which is its explicit process to confirm structural system performance under fire exposure. This is a valuable resource for new building project stakeholders, including building officials, fire marshals or the appropriate Authority Having Jurisdiction (AHJ) for final approval.

    ASCE SEI prepared this exemplar guidance document with exclusive grant funding from the Charles Pankow Foundation. The project would not have been possible without the financial support to the Charles Pankow Foundation from the following project sponsors: American Institute of Steel Construction, American Society of Civil Engineers Industry Leaders Council, ArcelorMittal and MKA Foundation.

    Performance-Based Structural Fire Design is available as a free download from the ASCE Library, the Structural Engineering Institute, and the Charles Pankow Foundation.

    ASCE


    | mérnökvagyok.hu
    2020.10.09 17:07

    Látványos videót tett közzé a Budapesti Fejlesztési Központ a tervezett új, Dél-Budát és Dél-Pestet összekötő Duna hídról. https://www.youtube.com/watch?v=OiYQlu_O4eo

    Budapest új körútjának fejlesztéséről október 12-én, 17 órától online lakossági fórumot tartanak (bfk.hu/forum).


    2016-ban döntés született arról, hogy az Új Duna-hídhoz (közismertebb nevén a Galvani hídhoz) kapcsolódó úthálózatot a Fehérvári úttól az Üllői útig kell megtervezni, a tervezési feladatok megvalósítására pedig a Nemzeti Infrastruktúra Fejlesztő Zrt. kapott megbízást.

    2017-ben a Kiemelt Kormányzati Beruházások Központja nemzetközi tervpályázatot bonyolított le, melynek eredményeként 2018 áprilisában választották ki Budapest, emblematikus Új Duna-hídjának tervezőit, holland UNStudio és az brit Buro Happold Engineering alkotta tervezői konzorciumot, akik egy olyan 2×3 forgalmi sáv széles híd terveit vetették papírra, amelyen az autóforgalom mellett ugyanilyen prioritást kaphat a közösségi közlekedés, illetve a környezetbarát közlekedési módok: a hídon villamos haladhat, kétoldalt széles gyalogos járdák, kerékpárutak is kialakításra kerülnek.

    Ami a hídhoz kapcsolódó úthálózatot illeti: az eredetileg tervezett nyomvonal Gubacsi út és Üllői út közé eső szakasza a Kiserdőt jelentős mértékben érintette volna, ezért a kialakuló lakossági tiltakozások hatására a tervekre többféle alternatív javaslat született.

    Végül 2020. február 27-én a Fővárosi Közfejlesztések Tanácsa – a Fővárosi Önkormányzat és a Kormány közös városfejlesztési szerve – úgy döntött, hogy Budapest belváros forgalomcsillapítása, valamint a külvárosi kerületekben élők közlekedési lehetőségeinek javítása érdekében megerősíti az Új Duna-híd és az úthálózat első szakaszának (a Fehérvári úttól a Gubacsi út-Illatos úti csomópontig) megépítésének szükségességét.

    Ezzel egyidejűleg az úthálózat második szakasza kapcsán a tanács a Gubacsi út-Illatos úti csomópontból kiindulva 2 irányban összesen 6 műszaki változat kidolgozását és hatásvizsgálatát rendelte el.

    Ezek közül 4 műszaki változat esetén az út a Gubacsi úti csomópontot elhagyva a Határ út irányába kanyarodik, és így éri el az Üllői utat. 2 műszaki változat esetén az út a Gubacsi úti csomópontot elhagyva a Ferencvárosi rendezőpályaudvart keresztezi, majd az Ecseri úton keresztül éri el az Üllői utat. Arról, hogy a 6 változat közül melyik valósuljon meg, 2020. december 31-ig kell döntést hoznia a Fővárosi Közfejlesztések Tanácsának.

    A döntés meghozatala során az érintett lakosság véleményét is figyelembe veszi a Fővárosi Közfejlesztések Tanácsa, ezért az elkészült nyomvonalváltozatokat társadalmi egyeztetésre bocsájtották, ami elérhető a https://budapestujkorutja.hu webcímen.

    Forrás: BFK


    | Octogon
    2020.10.09 15:07

    Közel 20 000 négyzetméteren kínál majd irodahelyiségeket és egyéb szolgáltatásokat jövő nyártól.


    | Tervlap
    2020.10.09 12:07

    Teleki József főispán egy katonai árverésen jutott hozzá ahhoz a foghíjtelekhez, melyre 1789-ben bérházat építtetett. Miután ő maga sosem lakott ott, 1816-ban a magyarországi hadak főparancsnoki tisztjét átvevő Ferdinánd főherceg beköltözött a falai közé, de 1850-től már a királyi kancellária hivatalait találjuk itt. József főherceg 1892-ben vásárolta meg a kincstártól...


    | Tervlap
    2020.10.09 11:08

    A legégetőbb problémák Az Építési Vállalkozók Országos Szakszövetsége (ÉVOSZ) idén szeptemberben a koronavírus okozta építőipari nehézségekről is készített felmérést. A kérdőívet kitöltők között 400 építőipari kivitelező, illetve tervező vállalkozás szerepelt. A szeptemberi felmérésben részt vett vállalkozások elmondása szerint a piaci tevékenységüket leginkább akadályozó tényező a szakemberhiány volt, a második helyen...


    | AECbytes Blog
    2020.10.08 21:31

    In this article, Erik Hultgren of Tech Soft 3D, discusses the advances made in visualization within the AEC space that keep making it taking quantum leaps forward, unlocking exciting new use cases and capabilities.

    The combination of hardware, software, and computing resources that is now available means that everything has scaled up tremendously, enabling the AEC industry to venture into some exciting areas, starting with the ability to ensure that buildings are being built as designed.

    URL: http://www.aecbytes.com/viewpoint/2020/issue_94.html


    | mérnökvagyok.hu
    2020.10.07 16:07
    Megnyílt a 39. Construma építőipari és otthonteremtési szakkiállítás október 7-én Budapesten, a Hungexpo vásárközpontban csaknem 150 kiállító mutatkozik be október 7-11. között.

    Boros Anita, az Innovációs és Technológiai Minisztérium építésgazdaságért, infrastrukturális környezetért és fenntarthatóságért felelős államtitkára elmondta, az építőipar termelékenysége 2017 óta folyamatosan bővült, 2019-ben pedig a rekordok éve volt. A koronavírus-járvány magyarországi megjelenése ezt a folyamatot törte meg. Kiemelte, a járvány belföldi megjelenésére reagálva a kormány gyorsan lépett, és a magyar gazdaság további fejlődése érdekében kidolgozták a gazdaságvédelmi akciótervet, amely egyebek mellett a beruházások ösztönzését, és a munkahelyek megtartását is célozta. Az akciótervnek köszönhető, hogy az építőiparban júniusban már a javulás jelei mutatkoztak – tette hozzá.

    Boros Anita beszélt a nemzeti fenntartható építésgazdasági startégiáról, amelyben fontos célkitűzésük, hogy Magyarországon legyen a legegyszerűbb és legkönnyebb építeni, hogy Magyarország ebből a szempontból is vonzóvá váljon a befektetők számára.

    A megnyitót követően adták át a Construma díjakat. Idén ezt az elismerést a Bachl Hőszigetelőanyag-gyártó Kft., a Horizont Global Kft., az Internorm Ablak Kft., valamint a Nilan Légtechnika Kft. és a Solar Hero Innovációs és Megújuló-energia Zrt. vehette át. (MTI)


    | mérnökvagyok.hu
    2020.10.07 09:26

    Ahogy arról korábban beszámoltunk (), júliusban zajlott az 1980-as évektől napirenden lévő velencei árvízvédelmi rendszer első tesztelése. A nyári próbaüzem után, október első hétvégéjén szükségessé vált a Mózes-gátrendszer éles bevetése: 130 centiméteres emelkedést jósoltak a szakemberek – jóval a tavaly novemberi Velencét sújtó és pusztító 187 cm-es áradás alatt, – de így is megbizonyosodhattak az ott tartózkodók arról, hogy a mélyen a vízszint alatt fekvő területek is szárazak maradtak.

    A cölöpökön álló észak-olasz város az éghajlatváltozás és a globális felmelegedés miatt fokozatosan süllyed, komoly árvizek károsítják, melyre a mobilgát-rendszer jelentheti a megoldást. Október első hétvégéje szó szerint vízválasztó pillanatot jelentett Velence számára, amikor a velencei lagúna bejáratához telepített 78 árvízkorlát eltorlaszolta az évszakos dagályt, amely rendszeres áradást okoz október és március között Velencében.

    Az előrejelzésre való tekintettel a kikötői hatóságok időkorláttal megtiltották a hajózási forgalmat a három hozzáférési ponton keresztül, ahol az akadályok vannak felszerelve.

    „Ma minden szárazon maradt. Megállítottuk a tengert” – jelentette be Luigi Brugnaro, a város polgármestere az újságíróknak, és ünnepélyesen emelte poharát arra a néhány mérnökre és tisztviselőre, akiknek a Mózes névre keresztelt, több milliárd eurós árvízvédelmi projekt köszönhető. A velencei lagúnák bejáratát őrző, 78 élénk sárga gátból álló hálózat felemelkedett a tengerfenékről, amikor az erős szél és az eső miatt emelkedni kezdett a víz szintje, megvédve ezzel a történelmi várost.

    *Videó hír: *

    *Forrás: *


    | mérnökvagyok.hu
    2020.10.07 09:13
    Újabb fontos lépcsőfokához érkezett a Lánchíd felújításának kivitelezéséről szóló közbeszerzési eljárás. Szeptember végén lezárult a részvételi szakasz, amelyből kiderült, hogy mind a négy jelentkező megfelelt a felhívásban megfogalmazott elvárásoknak. A négy ajánlattételre felhívott ajánlattevőnek 2020. október 28-ig kell benyújtania ajánlatát.

    Sikeresen zárult a Lánchíd közbeszerzési eljárásának részvételi szakasza. A négy jelentkező közül ugyanis mindegyik megfelelt a részvételi felhívásban megfogalmazott elvárásoknak. Így a BKK mind a négy társaságot felkérte az ajánlattételre az eljárás második, ajánlattételi szakaszában. Ezáltal teljesült a Fővárosi Önkormányzat és a Budapesti Közlekedési Központ célja, hiszen több szereplő vehet részt a közbeszerzésben.

    Az ajánlattételi szakasz a dokumentumok feltöltésétől kezdődően 25 nap. A kiválasztott gazdasági szereplőknek – az A-Híd Építő Zrt-nek, a Közgép Építő- és Fémszerkezetgyártó Zrt-nek, az SDD Konzorciumnak (DÖMPER Kft., Subterra – Raab Kft., Pannon-Doprastay Kft.) és a STRABAG Általános Építő Kft-nek – 2020. október 28-ig kell elküldeniük az első ajánlatukat.

    Kedvező ajánlatok esetében a BKK 2021 februárban köthet szerződést a leendő kivitelezővel. Magyarország szimbólumának felújítása egy hónappal később, márciusban kezdődhet el, amennyiben Magyarország kormánya is biztosítja az ígért támogatást. A megújult Lánchidat – az előzetes ütemezés alapján – 2023-ban vehetik újra birtokba a közlekedők.


    | Tervlap
    2020.10.05 12:48

    Lezsák Sándor, a Népfőiskolai Alapítvány elnöke a székházátadáson köszöntőjében elmondta: a kiemelt kormányzati beruházás hátterében a magyar költségvetés, az adófizető polgárok támogatása és jogos elvárása van. Ez az épület szolgálja "a magyar kultúra szent ügyét", a Kárpát-medencei magyarok közösségi életét – tette hozzá. A történelmi jelentőségű helyszínen átadott új központ...


    | Rhino News
    2020.10.05 12:07

    Do you want to use dynamic blocks in Rhino?

    Do you want to learn how to create your custom parametric objects? In this webinar, you will learn what the VisualARQ Grasshopper styles are. You will see some examples of how to bring your Grasshopper definitions into custom parametric objects in Rhino.

    No Grasshopper knowledge is required to follow this webinar. But you will learn what’s behind a VisualARQ object created by a Grasshopper definition, and the unlimited possibilities this combination of tools offers.

    The webinar will take around 30 minutes, with some Q&A.

    Registration is free but seats are limited...


    The variability in netting system quality and design illustrates the critical role of third-party experts when selecting fall protection and debris control systems for construction projects

    By Jeff Elliott

    Construction managers, general contractors, and building owners are certainly familiar with safety netting systems and the reasons to install them, which include protecting workers and debris from falling from structures, as well as façade and ceiling containment. They also believe these passive systems create and maintain a safe work environment.

    However, when it comes to specifying the appropriate solution for a construction project, many see netting systems as, well, pretty much all the same.

    In reality, this could not be further from the truth, given the broad variability in the quality and construction of nets, suitability for the stated safety purpose, quality of testing, and other factors that impact the ability to meet a broad range of national and state fall protection and debris control standards.

    While this list is extensive, it only serves to underscore the fact that netting system selection should squarely rest in the domain of experts and engineers, and not viewed as a mere commodity item. As such, contractors and building owners often rely on third parties with a wealth of netting-specific knowledge and expertise when devising safety plans or designing and installing rented or purchased nets and systems.

    “You can’t just put a netting system together that you feel is going to work, only to realize at the end of the day it was not sufficient for the purpose,” says Harry Weidmyer of Construction Safety Service and Solutions. “You are taking something that is a vital part of safety on a project and so you can’t take shortcuts and put up netting that seems easier, or maybe requires a little less labor.”

    There are other reasons that well manufactured and designed netting system also makes good business sense beyond the safety aspect. It can also reduce insurance costs, improve safety ratings, speed productivity, boost worker morale, and create a positive public image.

    No Shortcuts

    As vice president of risk management at a major construction firm in New York for 20 years and now president of his own company, Weidmyer has witnessed the variability in netting system installation first hand.

    Given his company’s focus on risk assessment and loss control, Weidmyer has had the opportunity to work with contractors in New York, Connecticut, New Jersey, and Florida to review their insurances and to monitor their safety program and protocols.

    Outside of New York City, which is known for the some of the most stringent netting system codes in the country, Weidmyer says, “I’ve seen netting system installed by contractors that I feel slice it thin in terms of protection. For example, they install a debris net that serves only the minor purpose of catching light debris, but if somebody fell into it, it is not going to support them.”

    Weidmyer says that in New York City, the nets specified and installed are often expected to serve double duty of catching heavy debris as well as providing personnel fall protection. The codes even require paperwork that verifies the integrity of the manufacture of the net itself.

    OSHA Guidelines Subpart M and Article 19 of the NYC Building Code require specific safety systems on a construction site. To meet the guidelines, contractors must submit a site safety plan to the city.

    For high rise buildings 15 stories or more, netting is typically mandated in the safety plans from the 6th floor up. Nets are the primary passive fall arrest system option on the market and usually the most cost effective. They provide not only fall protection and the separation of trades, but also protection of workers and the public, in addition to other property below from falling debris.

    In addition, netting can be used for other purposes including as a scaffold and barrier netting and for façade containment, to protect the public from falling debris from deteriorating buildings until permanent repairs can be undertaken.

    For the past 35 years, Weidmyer says he has relied on Pucuda – Leading Edge for the netting system designs in his safety proposals. Pucuda – Leading Edge designs the system and can submits the relevant paperwork and follows through until it is authorized by the Department of Buildings, if needed.

    Pucuda – Leading Edge is one of the few netting system manufacturers that produces nets in the United States and that has a history of innovation in product design. The company was founded 27 years ago by hands-on netting expert John Rexroad, President, Founder and CEO of the company.

    Weidmyer says the company is basically a one-stop-shop and he also turns to them for the nets as well, all of which conform to all ANSI, OSHA, Army Corps of Engineers, and ASTM standards.

    “John is a phenomenal net system designer and so is his team,” says Weidmyer. “I have recommended him to quite a few contractors in New York City because I know his systems are designed properly and there is no second thought or concern about them working properly.”

    Cape Canaveral Launch Towers

    Pucuda is also involved in a unique project at the Kennedy Space Center at the Air Force station at Cape Canaveral, supplying netting systems for a structural steel project to construct a launch tower and a lightning strike tower.

    “On a portion of this particular project, we are building two towers and the primary function of the netting is to catch debris,” explains Alan Bukis of S&R Enterprises, the on-site project manager for the structural steel construction company. “So, if somebody is working up on level 400 and accidentally drops something, the debris netting will catch it before it goes to the ground and potentially hurts somebody.”

    In addition, the nets are technically rated for fall protection even though it is not the intended use. In addition to the netting, workers are expected to tie off using a fully body harness whenever they are six feet above the floor.

    These towers represent protection for the first new build of a Launch Pad in several decades. Therefore, it was important for S&R to interview several netting manufactures.

    “Overall, [Pucuda – Leading Edge] had the best presentation as far as we were concerned,” says Bukis. “John Rexroad definitely knows the netting industry inside and out, and it was very evident in our initial discussions.”

    One important aspect of the presentation was a review of samples of the netting, brought in by two of the three companies. “By appearance alone, you could see there was a higher quality netting with Pucuda – Leading Edge,” says Bukis. “The other company brought a sample and it was a considerable difference.

    Quality in the manufacturing and materials of netting is a major factor in the selection process. Many nets supplied by U.S. based companies are imported from China or India where the manufacturing process is driven by supplying an inexpensive product in mass quantities.

    Even nets that appear adequate may have quality issues lurking under the surface that are not easily identifiable by the untrained eye. One example is a deterioration condition caused when an overseas supplier manufactures a net with a linked polymer that begins to deteriorate almost immediately. The condition is referred to as “wooly bear” syndrome, due to its appearance. This can dramatically affect the longevity and safety of the products.

    Although in the construction industry nets are often rented for a project, S&R Enterprises decided to purchase the nets from Pucuda in anticipation of additional future projects. For this reason, it was even more important the net and system was manufactured with the highest quality materials and with longevity in mind.

    Bukis says there were installation challenges to overcome as well., as one of the towers was a sloping triangle that progressively narrowed as it went up.

    “When our team was installing the nets, they had a ton of questions about installing the netting correctly,” says Bukis. “So, we asked John to come to the site.”

    “He is not afraid to come out and go up in a structure and actually look at the installation,” adds Bukis, noting that this was also during the COVID-19 pandemic. “Just him being here and knowing that he’s the expert and him confirming that the installation was correct alleviated all their concerns. So, it was definitely beneficial that he was willing to come out and do that.”

    With netting systems, the most well-designed and manufactured systems are those that go unnoticed and can be taken for granted. It is only when someone, or something falls and causes damage or injury to people or property and it makes the evening news that netting systems take center stage.

    With so much at stake, contractors and building owners would be well served to seek out expert advice from netting system experts to avoid installing defective products that fall below the safety standards.

    “It all comes down to safety,” explains Bukis. “If something or someone happens to fall, you are going to want the best nets available. I feel much more comfortable with a higher quality product, because the goal is, we don’t ever want any of our people hurt.”


    Jeff Elliott is a Torrance, Calif.-based technical writer. He has researched and written about industrial technologies and issues for the past 15 years.

    The post Avoiding Costly, and Potentially Deadly, Shortcuts in Netting System Selection appeared first on Civil + Structural Engineer magazine.


    By Jamie Hodges

    The construction industry is no stranger to prefabrication – it’s been used for decades as an efficient way to build components of a structure offsite and then transport and assemble them at the jobsite for less cost and less labor without compromising on quality. While this type of construction has been used by many in the industry, it’s popularity is growing given the many additional benefits it brings in a world dominated by COVID-19-related safety concerns, which include minimizing worker interactions and increasing social distancing. The following benefits have always been inherent to prefabrication but are even more so in the world of COVID-19.

    Better quality and control

    One of the top benefits of prefabrication is the ability to design and construct a high-quality product in a controlled environment. Unlike at a jobsite where there are different aspects of a project happening simultaneously, a prefabrication shop allows for a portion of the project to be built offsite in a quiet, weather-resistant, controlled environment. This provides for less distractions and less unknowns, helping to keep projects on track.

    Prefabrication is also typically planned in advance so you have a better sense of what needs to be created and can utilize a crew who has the skill set to construct the materials according to set standards, which are quality checked throughout the process. Put together, this helps contribute to better craftsmanship and better quality as well.

    Faster and more efficient

    Prefabrication helps accelerate your work since you’re not out in the field subject to weather delays or other distractions like trucks and traffic that can naturally slow a project down. You also usually have the same skilled workers assigned to the project who can hone in and complete it with less interruptions since they know what to expect, taking a lot of the guesswork out of day-to-day operations.

    Having the same crew work together can also give them a bit of insulation because they’re separated from other workers at the jobsite and thus at less risk of exposure. When the pandemic hit in March, many prefabrication shops didn’t skip a beat because they were able to social distance quickly and easily, ensuring proper safety precautions were taken immediately.

    Prefabrication also usually takes less people to produce and install, in addition to being done more quickly due to upfront planning and fewer subcontractor delays.

    Significant cost savings

    One of the biggest benefits of prefabrication is cost savings, which is the result of many of the previous benefits mentioned – i.e. anything that is more efficient, has less interruptions and requires less labor will naturally cost less. In fact, it’s not uncommon for prefabrication to cost anywhere from a third to half as much as producing and installing on site.

    It’s also not uncommon to prefab in more than one shop, sharing production with partners whom you know and trust. If you sell your services as a package deal, it can help drop the price and further increase your ability to win the job, in addition to helping should you have scheduling or capacity issues.

    One recent noteworthy project developed in partnership was between ICM Colorado, a general contractor with locations in Denver and Pueblo who specializes in prefabricated steel projects, and rocket manufacturer United Launch Alliance (ULA). The project entailed developing prefabricated structural columns and beams for a rocket simulator test pad, which was developed after three design changes to ensure precision tolerances. ICM Colorado was able to construct all of the steel offsite, helping to speed up the timeline and reduce the overall project cost.

    Constructing offsite can also enable a client to keep their facility operational during construction, helping them avoid any reduction in revenue since a large portion of construction happens offsite, minimizing interference with normal operations. This can be a huge selling point when bidding for projects as it provides clients with additional cost savings.

    Less waste and more environmentally friendly

    Finally, because prefabrication tends to be pre-planned, materials can be more accurately measured leaving less waste. Materials from one project can also be easily recycled in-house towards the next project vs. sending them to a landfill.

    Prefab shops also tend to have exposure to the outdoors so employees can easily work on projects outside, helping with ventilation. As we know now, this is another benefit to COVID-19-related health concerns, as it enables workers to have easy access to good air circulation while still benefiting from a more tightly-controlled environment.

    Final thoughts

    Prefabrication is clearly here to stay and will only continue to grow in popularity given its many benefits – both those that were always inherent to the industry, but which are even more helpful in today’s world. The faster the industry adopts prefabrication, the better off many contractors will be in ensuring that their projects are done quickly and efficiently, for less cost and with less environmental impact, all without compromising on quality. Plus, prefabrication helps keep workers safer by being in a controlled environment with less people and thus less risk for infection. At a time when safety is paramount, there is no better benefit than that.


    Jamie Hodges is the Executive Vice President of Industrial Constructors/Managers, Inc. and has worked as a specialty contractor in industrial construction and management for over 15 years.

    The post The Benefits of Prefabrication in a COVID-19 World appeared first on Civil + Structural Engineer magazine.


    Bringing to life California’s first long-span cable-stayed bridge

    By Josh Mattheis and Matt Carter

    After over 50 years in operation, the Gerald Desmond Bridge is at the end of its useful life and will be replaced with a new six-lane cable-stayed main span bridge slated for completion in late 2020. The 2000-foot-long Gerald Desmond Bridge replacement is set to become California’s first long-span cable-stayed bridge.

    Approximately two miles of new cast-in-place concrete approach viaducts rise 200 feet off the ground from both the east and the west as they transition to the main span cable-stayed bridge. Composed of two 500-foot back-spans and a 1000-foot main span, the new main span bridge provides increased vertical clearance over the Port of Long Beach back channel for future generations of commercial maritime shipping. Safe, optimized flow of people and goods is underpinned by the bridge’s geometric and structural design, featuring truck climbing lanes and shoulders on both sides of the highway for reduced congestion and a state-of-the-art Type 3 AASHTO global seismic design strategy.

    An incredible fifteen percent of all North American maritime container traffic crosses the Gerald Desmond Bridge, making it a critical infrastructure link and a vital component of the regional and national economy. The bridge replacement responds to its critical role by providing a resilient, efficient, and aesthetically distinct structure in terms of performance, maintenance and architecture. The aesthetic dimension of the main span bridge is accented by faceted 515-foot-tall mono-pole towers augmented by customizable architectural lighting, making the new bridge a landmark for the Port and the City of Long Beach.

    Arup is prime designer for the project and Engineer of Record for the main-span bridge Gerald Desmond Bridge Replacement Project and high-level approach viaducts. Arup also provided the cable-stayed bridge erection geometry control and erection engineering support services.

    Figure 1: Depiction of tower dampers at maximum seismic distortion. Photo: Port of Long BeachDouble Texas U-turn

    The project’s bid package reference design (RID) proposed a grade-separated flyover ramp for west-bound traffic seeking to exit the main roadway and cross to the southern side of the project. Arup’s value engineering identified that the same functionality could be delivered while eliminating the entire flyover structure. Arup proposed a roadway geometry that passed below the main roadway with a dedicated free-flowing two-lane U-turn, facilitated by a new underpass constructed through the existing main roadway embankment. As this is a common geometric configuration in the state of Texas, the arrangement is dubbed the “Texas U-turn.” Through innovative highway engineering, Arup rearranged the Port access roads so that truck traffic accessing the terminal facilities would use the same underpass both to get on and off the bridge, hence the “Double Texas U-turn” moniker.

    The proposed solution reduced project costs by close to $70 million while providing numerous functional advantages. Land previously reserved for the RID flyover ramp bridge piers is now free to be used for other, revenue generating purposes. It also reduced the carbon footprint associated with construction volume, as well as reduced environmental risks: A known hydrocarbon contaminant plume in the area meant that deep foundation tailings would have had to been processed as hazardous waste. By removing the need for foundations, this cost and risk were eliminated.

    Seismic design

    The Gerald Desmond Bridge Replacement Project is the only cable-stayed bridge of its size on the highly seismic west coast of the United States. Arup designed the bridge towers and end bents to remain essentially elastic during seismic events in alignment with an AASHTO Type 3 seismic design strategy. To achieve this, the bridge deck is seismically isolated from the towers and end bents by and array of 34 structurally-fused viscous hydraulic dampers.

    Thanks to integrated structural fuses, the viscous hydraulic dampers only activate during seismic events superior to the one in one-hundred-year return period event. The damper fuses take the form of structural steel tubing encompassing the dampers, designed to release at a force corresponding to the controlling seismic event. After the steel fuse releases, the viscous dampers begin to dissipate cyclic energy in the same way that a car’s shock absorbers do on a bumpy road. The fused damper design reduces maintenance requirements by isolating sensitive damper components from ambient cyclical movements, ensuring optimal performance during the design seismic event.

    Fuses and dampers are designed specifically for ease of maintenance, redundancy and future-proofing. Integrated pressure gages, observations windows, and transducers facilitate routine maintenance. The overall quantity of dampers was determined to make the damper size manageable for installation, maintenance, or replacement. Dampers and fuses are provided by Taylor Devices, Inc. Testing of the full-scale dampers was performed at the University of California, San Diego (UCSD) laboratory.

    Figure 2: Gerald Desmond Bridge main span bridge tower sectional evolutionReducing the need for maintenance

    Figure 3: Development of the tower sectionArup’s monopole tower and fused viscous damper solution provides a non-invasive post-seismic remediation plan where the bridge deck is repositioned with jacks, and broken fuses are replaced without the need to alter the bridge substructure. Towers and end bents are simplified to be less congested with fewer items to inspect and maintain, while means of access are provided to conveniently access each viscous damper for inspection or fuse replacement without the need for hoists or manlifts.

    Tower geometry, aesthetics and practicality

    The two 157-meter high main span bridge mono towers are a dominant aspect of the project’s visual impact. Tower geometric form is critical.

    Once the project team decided on a single-shaft tower design, the tower’s geometric form began to take shape. A conical form was originally developed, because the circular form is visually pleasing and responds well to the pattern of the stay cable anchorages and governing seismic demands, which can be of the same order of magnitude in any direction.

    The team reviewed a similar conical geometry adopted for the 308-meter tall Stonecutters Bridge towers. In that case, the conical form was constructed with a self-climbing formwork system designed to adapt to the reducing radius of the section. However, given the shorter height of the Gerald Desmond Bridge Replacement Project towers, such a specialized formwork system would not be economical. The conical form was not developed further.

    Two further sections were contemplated:

    • A modified cone with constant radius corners and a tapering flat section
    • An eight sided geometry transforming from an octagon base to a square form at the top.

    Of which the octagonal base was retained.

    The octagonal transformation is carried out by tapering four of the eight sides while maintaining the other four at a constant dimension. This approach lends itself to an efficient climbing formwork arrangement because out of the eight jumping vertical formwork components, only four change dimensions at each jump.

    Figure 4: Evolution of tower cross section from tower base (left) to top of tower (right)A design decision was made to taper the faces which are orthogonal to the bridges primary axes. Tapering faces at 45 degrees to the primary axes would have resulted in a “square geometry” that is incompatible with stay cable geometry: the fan of cables will intersect with the corner of the tower meaning that some of the anchorages will pass through the section’s corner. Keeping the diagonal faces constant resulted in a “diamond geometry”, simultaneously resolving the geometric conflict between cable stays and section corners and creating a unique and instantly recognizable tower form.

    The octagonal tower geometry uses light and shadow to define the form while bringing practicality to the construction. The team considers the “diamond geometry” solution to be aesthetically superior to the modified cone and more efficient in construction.

    The tower cross-section is a great example of form meets function and exemplifies the total architecture perspective of design and construction.

    Moving forward

    Many technological and performance innovations were achieved during the design and construction of the Gerald Desmond Bridge Replacement Project, of which only a very few have been touched upon here. The end result is a structure that successfully rationalizes performance, maintenance, aesthetic and environmentally efficient objectives into a best-fit product, to the benefit of all.


    Matt Carter is a Principal in Arup’s New York office, and serves as the Bridge and Civil Structures Skills Leader for Arup’s Americas region. He has 23 years’ experience in the conceptual and detailed design of long span and complex bridge structures in North America, East Asia, Europe, Africa and Australia. Notable projects include major cable stayed bridges such as the Samuel de Champlain Bridge in Montreal, Gerald Desmond Bridge Replacement in California, the Queensferry Crossing in Scotland and Stonecutters Bridge in Hong Kong. Through his work on major bridge projects, Matt has gained significant experience in the seismic and aerodynamic design of bridges and ship collision risk. In recent years, he has worked primarily on design-build projects and public private partnerships with both owners and contractors as clients, gaining unique insights by working from different perspectives.

    Josh Mattheis is an Associate Principal in Arup’s Los Angeles office. He has 17 years of experience in design and design management of large rail and roadway turn-key design and build contracts. After working for international design firms and contractors, his experience is balanced between both. Josh enjoys leveraging this experience to create optimized and integrated designs that provide value to all parties. Recent projects include design and design management work on the Gerald Desmond Bridge project at the Port of Long Beach, followed by the Port Miami Tunnel project and the Gautrain Rapid Rail project. Typical design activities on these (and previous projects) include alignment optimization, selection of structure types, development of adapted construction methods and detailed design production in collaboration with state, municipal and county agencies.

    The post Gerald Desmond Bridge Replacement Project: appeared first on Civil + Structural Engineer magazine.


    | STRUCTURE magazine
    2020.10.02 19:36

    Development, Achievements, and Possibilities

    Cable-stayed structures are the youngest, fastest-developing, and most promising bridge systems.

    Cable-stayed bridges are a subcategory of suspended structures. A cable-stayed bridge is similar to a suspension bridge in having towers and a deck-girder supported by cables; however, its diagonal cables transfer the vertical loads from the deck directly to the towers. Thus, the main deck-girder of a cable-stayed bridge works like a continuous beam on cable supports (more flexible than pier supports) with additional compression force throughout the deck. A cable-stayed bridge is also a prestressed system as its cable-stays are additionally tensioned to counterbalance a significant part of the vertical loads on the main deck-girder.

    The Strömsund Bridge in Sweden, completed in 1956 with a 182-meter (597-foot) main span, is considered the first modern cable-stayed bridge. For the following 65 years, cable-stayed bridges have seen a dramatic increase in both the number of new structures and in long-span achievements. By 1995, there were only 3 cable-stayed bridges with spans over 500 meters (1,640 feet); 25 years later, there are already 67 cable-stayed bridges with spans over 500 meters (including three over 1,000 meters or 3,280 feet). Another 29 with spans over 500 meters, with some over 800 meters (2,624 feet), are currently under construction.

    The efficient range of cable-stayed bridges is moving towards even longer spans. There is no other bridge structural system exhibiting such rapid development. Most cable-stayed bridges are visually beautiful, and some are among the most impressive of engineering achievements.

    Origins and Precedents

    The idea for the cable-stayed system was perhaps inspired by the drawbridges of medieval castles and the rope-braced masts of tall ships. The very first documented image of a cable-stayed bridge appears in the Machinae Novae, a book by Fausto Veranzio published in 1615.

    Predecessors for modern cable-stayed bridges appeared in the 19th century in the form of different hybrid combinations of suspension systems with additional diagonal straight cables, as in the case of the Albert Bridge, UK (1873). The best known of these hybrid structures is the Brooklyn Bridge, New York, 1883, with a 486-meter main span (1,594 feet), for which John Roebling used diagonal cables for stiffening the structure.

    Figure 1. Russky Island Bridge.Figure 1. Russky Island Bridge.

    In the 1960s and 1970s, the system was developed further to replace many of the bridges destroyed in Germany during World War II. In this period, the system was also used for roof structures requiring long, column-free spaces in buildings. Initially, cable-stayed structures were used for bridge spans of 60 to 250 meters (196 to 820 feet) but today they span much longer distances and are the only system that challenges suspension bridges in super-long spans. Their spans grew to 302 meters (990 feet) in 1959 with the Severin Bridge (Germany), to 404 meters (1,325 feet) in 1974 with the Saint Nazaire Bridge (France), and 856 meters (2,808 feet) in 1995 with Michel Virlogeux’s Normandy Bridge (France). Today, the Russky Island Bridge (Russia) has the longest span of this system, 1,104 meters (3,622 feet) achieved in 2012 (Figure 1).

    In the United States, we can mention the second Sunshine Skyway Bridge with a span 366-meter (1,200 feet) in 1987 (Florida), the Dames Point Bridge with a 396-meter span (1,300-foot) in Florida, and the Arthur Ravenel Bridge with a 471-meter span (1,545-foot) in 2005 (South Carolina).

    System Specifics

    The main elements of a cable-stayed bridge are towers or pylons, deck girder(s), cable-stays, anchorages, and foundations. Tower and pylon are interchangeable terms; lighter, slender towers are often called pylons. The classic cable-stayed bridges are symmetric with one central span, two side spans, and two towers; such are most cable-stayed bridges with spans above 600 meters. The back-up cables may extend over several side spans.

    Asymmetric cable-stayed bridges have one main span and one side span, with a single tower. Multiple-span cable-stayed bridges have two or more (usually equal) main spans. Several examples are shown in Figure 2.

    Figure 2. Span options: main with two sides spans, asymmetric and multi-span.Figure 2. Span options: main with two sides spans, asymmetric and multi-span.

    Some sub-divisions are used for cable-stayed bridges: extradosed, under-spanned (under-deck), cradle, inverted Fink truss, and tensegrity. The cables at the towers can be arranged in parallel (harp), fan, star, or mixed configuration. Various structural solutions are used for the towers: single pylons, double-leg portals (vertical, slightly angled, free-standing, or interconnected as a portal frame, with “A,” “H,” “Y,” or inverted “Y” shaped arches).

    Figure 3. Tower configuration options.Figure 3. Tower configuration options.

    The towers can be continuous above and below the deck supporting both the deck and the cables, or the upper part can support only the cables while the deck-girder is supported directly by piers. Examples are shown in Figure 3.

    The primary construction materials used in cable-stayed bridges are:

    • For decks: reinforced or prestressed concrete, composite concrete-steel, or orthotropic steel decks;
    • For deck-girders: beams of prestressed concrete or steel, box girders of prestressed concrete or steel, similar to those in modern suspension bridges;
    • For towers: steel, reinforced or prestressed concrete, composite steel-concrete;
    • For cables: high-strength steel wires, usually 270 grade (270 ksi, or 1,860 MPa), built from 7-wire, ⅜-inch (9.5 millimeters) strands per ASTM A886, other higher-grade steel wires, carbon fiber-reinforced polymers (CFRP), or composites. Prestressed concrete has been used in the past, but should be avoided as it has been proven unsafe on some failures such as the Morandi Bridge;
    • For piers and foundations: reinforced concrete with or without piles depending on the soil.

    For long-span bridges, foundations on soft soils, or for bridges in high seismic areas, it is preferable to use predominantly steel structures to reduce the self-weight and the related earthquake forces.

    Conceptual Design

    The most important part of bridge design is the overall concept for the structure and its elements: the selection of the appropriate structural system for the bridge considering its specific function, site location, and required spans. A well-selected concept determines the efficiency and economy of the bridge, saves materials, cost, and construction time. Good design concepts minimize problems and future difficulties both in the design office and on the construction site.

    For the design of early cable-stayed bridges, engineers used a relatively small number of cables. After acquiring more experience and with the introduction of structural design software, engineers were able to use a larger number of cable stays, reducing the demand on the deck girder and leading to greater efficiency and longer spans.

    The basics of cable-stayed bridge design are as follows: the vertical loads on the deck are supported by diagonal cable stays that transfer these loads to the towers. At the tower, the horizontal components of the cables from the main span are in balance with those from the side/adjacent spans. The towers support and transfer the vertical load to the foundations. Similarly, the cumulative compression horizontal components of the loads from the main span are in balance with the compression load components of the side spans. Therefore, the entire bridge system is in balance with predominant compression forces in the towers and the deck system, and with tension forces in the cable stays. The system is self-balanced, provided that all elements are designed correctly to sustain the maximum demand from the highest possible combination of loads.

    The challenge for the design engineer is to select an appropriate combination of the multiple possible variations of towers, cable-stay arrangements, and deck systems. Like all suspended structures, cable-stayed bridges are sensitive to deformations and it is necessary to check the deformed condition of the system for all load combinations, including those during the different phases of construction.

    Today’s structural design software greatly assists engineers in the calculation of cable-stayed bridges. After choosing the main parameters of the system, it is essential to establish the start-up dimensions and sections of the deck-girder, cables, and towers. A simple design approach will help in setting up these dimensions.

    For a start, the designer can use a substitution simply-supported beam for determining the approximate bending moments for the main span deck-girder. The upward cable-stays pretension can offset most of the moments from permanent loads on the deck. This is achieved with additional tensioning of the cables after erecting the main elements to counteract permanent loads, resulting in minimal vertical bending in the deck-girder. The cables should be additionally tensioned to counteract 50% of the combined temporary downward loads (live loads, wind, snow, ice, and earthquake). This way, the working bending moments of the deck-girder will vary during operation approximately between 50% of the positive moments (from the worst temporary load combination) to 50% of the negative moments from temporary loads. This “first step” determines the design moments for the main span deck-girder. The compression in the deck-girder due to the horizontal components of cable stays forces is the cumulative sum of these components, approximately 55 to 65% of the total vertical loads on the main span depending on the span, the number of cables, and the height of cable connections at the tower. The cumulative compression force (ΣPc) in the deck-girder is equal to the sum of all compression forces Pci at cable connections (Figure 4) at the deck: the tension cable force Pcable = Pv/sin α,

    Pci is the compression force in the deck-girder from the horizontal component of the cable force,

    Pvi is the vertical DL + LL force applied at the cable connection at the deck-girder plus the vertical component of the additionally-applied tension force,

    Li is the horizontal distance from this connection to the tower, and

    Ht is the height of this cable connection at the tower above the deck.

    A simplified initial calculation for the cumulative compression force is provided by:

    where:

    ΣPc is the cumulative compression force in the deck-girder, maximum at towers,

    ΣPv is the sum of all downward vertical forces on the main span deck,

    Lmax is the main span length,

    Ht is the height of the cable connections at the tower above deck, as shown in Figure 4 for fan or harp cable configuration, and

    Lgr is the total length of the cable group for harp configuration.

    Figure 4. Compression forces in deck-girder: at single cable (a); and total compression force for “fan” (b) and “harp” (c) cable configurations.Figure 4. Compression forces in deck-girder: at single cable (a); and total compression force for “fan” (b) and “harp” (c) cable configurations.

    The sum of the horizontal forces of all cables at the tower (from the main span) is equal to the cumulative compression force in the main span deck-girder, balanced by an equal force on the opposite side.

    These calculations will allow the designer to establish the initial design dimensions for the cables, deck-girder, and tower to be used in the computer model for further adjustments and refinements of the system. The deck-girder has to be designed for the compression and bending from the cable-stay system and the typical bridge deck design for vertical dead and live loads. The initial approach described above will help to achieve the desired final goal faster.

    Efficiency and Economy

    Cable-stayed bridges are efficient in cost, materials, and construction time. They have better efficiency than other bridge systems, with the only competitor being suspension systems, while allowing for more straightforward construction methods. An additional advantage of cable-stayed bridges is their larger efficient span range from 100-meter spans (328 feet) to over 1,000-meter spans (3,280 feet).

    The multitude of possibilities of the system provide engineers and architects with many design options. The “mid-long range” structures allow more creativity, originality, and possibilities for innovative work. A cable-stayed bridge does not need to be extravagant. The most straightforward bridge with a “sincere” structure is often the best and is usually elegant and attractive.

    Cable-stayed bridges have a combination of elegance, slenderness, and a feeling of robustness. The national infrastructure’s demand for more bridges requires the priority of efficiency and economy.

    The art of engineering requires creativity and fantasy, but engineers should avoid repetitive and illogical shapes. Creativity is essential, but “excessive originality” should only be found in justified exceptions (e.g., Christian Menn and Michel Virlogeux).

    Pros and Cons

    The main system advantages are:

    • Fast and relatively easy construction, requiring less time to build
    • Less expensive
    • Multiple design options
    • Large efficient span range
    • Strong and resilient structures
    • Attractive appearance

    The main system disadvantages are:

    • Still inferior to suspension bridges for super-long spans
    • Requires checking deformations at all conditions
    • Requires experience in both design and construction

    Further Development

    Like all other bridge systems, cable-stayed bridges are continuously improved based on the development of high-strength materials and new construction technologies. More valuable for engineers are the modifications of established structural systems and newer sub-systems. In addition to the increased number of cable-stayed bridges with longer spans (above 600 meters or approximately 2,000 feet), there is increasing use of the system for pedestrian bridges. The lower loads and shorter spans allow engineers to explore new approaches, transforming the building of these bridges into a testing lab for innovation. As such, we may consider the extradosed, under-spanned, and inverted Fink truss sub-bridge systems, all oriented to improved efficiency.

    Figure 5. Hybrid cable-stayed and suspension bridge system for super long spans.Figure 5. Hybrid cable-stayed and suspension bridge system for super long spans.

    One area of further development is the pursuit of combinations/hybrids of cable-stayed and suspension bridge systems for achieving super-long spans. The idea is to reduce the suspension span length by moving the suspension support points inward along the span. This not only reduces the suspension span length but the required tower height as well while allowing a longer clear span. This is obtained with “cable-stay cantilevered alternatives” at the bridge towers, adding “on-deck” cable-stayed pylons (Figure 5). With 500-meter (1,640-foot) cantilevers and cable-stayed “on-deck” pylons used on each side of a total clear span of 3,000 meters (9,842 feet), the suspension part is reduced to 2,000 meters (6,561 feet). Such reduction would allow using main suspension cables of the size and type of those already used in bridges, like the Akashi-Kaikyo at 1991 meters (6,532 feet), for a much longer main span.

    Conclusions

    Based on current technical progress and fast development, cable-stayed bridges may reach spans 2,400 to 2,600 meters (7,600 to 8,500 feet) in a short while; such design will require towers about 500 to 570 meters tall (1640 feet to 1,870 feet), something achievable, considering already completed skyscraper structures. This will extend the efficiency range for cable-stayed bridges to very long spans above 2,000 meters (6,561 feet). A hybrid cable-stayed-and-suspension system would make possible even longer spans of up to 3,000 to 3,400 meters (9,842 to over 11,000 feet), incorporating a “pure” suspension bridge of “only” 2,200 to 2,400 meters (7,218 to 7,874 feet).

    Based on the efficiency and advantages of cable-stayed structures, American engineers and transportation agencies should consider more cable-stayed bridges when planning new projects. Greater use of cable-stayed bridges may upgrade the infrastructure with these efficient, faster built, and elegant structures. Making cable-stayed bridges more popular may also help our bridge engineering profession regain its position of leadership in the design and construction of long-span bridges.■


    | STRUCTURE magazine
    2020.10.02 19:36

    Reconnecting Communities through Creative Infrastructure

    The recently constructed Beehive Bridge in New Britain, Connecticut, and winner of the American Council of Engineering Companies (ACEC) Engineering Excellence National Merit Award, is a testament to the power of structures to connect people and connect to people. The Beehive Bridge reconnects long-divided neighborhoods, encourages pedestrian use, and represents its community through its singular design (Figure 1).

    Figure 1. Beehive Bridge elevation.Figure 1. Beehive Bridge elevation.

    A Community Divided

    When State Route 72 was installed through the center of New Britain in the late 1970s, rapid access to the adjacent interstate system was the driving force behind the construction. At that time, the fact that the sunken roadway ran straight through the middle of the city was a secondary concern. Though several bridges were installed to reconnect the now separate neighborhoods, connectivity to the downtown areas was irrevocably damaged. People found it more convenient to avoid the bridges and stay on their side of the highway. The result was a city divided by a highway installed to serve it.

    Merging Form and Function

    In visualizing a fix to this long-standing condition, New Britain Mayor Erin Stewart initially planned to incorporate public art into one of the Route 72 overpasses to create a public space that would draw people to cross the highway and shelter them from the highway bustle and noise. To help realize this vision, the City hired a design team led by engineering firm Fuss and O’Neill of Manchester, CT, along with design team members Svigals + Partners, Pirie Associates, and Richter & Cegan, Inc. The actualized design takes inspiration from the City’s seal, which includes bees, a beehive, and the motto in Latin of “industry fills the hive and enjoys the honey” that pays homage to the City’s industrial past.

    Figure 2. Pedestrian view from the sidewalk at day.Figure 2. Pedestrian view from the sidewalk at day.

    The unique focal point of the project is the pedestrian enclosure, which consists of more than 2,100 amber-honey-colored, ½-inch-thick polycarbonate panels arranged in the shape of a giant honeycomb. Its unique appearance shines as a landmark for the City and changes the landscape throughout the day. During daylight hours, the enclosure paints the bridge in ever-changing shades as the sun moves through the sky (Figure 2). At night, programmable LED lighting creates a 21st-century beacon inviting travelers to the City (Figure 3).

    Figure 3. Bee sculpture watching over the structure at dusk.Figure 3. Bee sculpture watching over the structure at dusk.

    Transformation

    The existing bridge carries Main Street over Route 72. The bridge is 270 feet long, split evenly over two 135-foot spans. It is a typical overpass from its time, consisting of 10 haunched steel plate girders supporting a composite concrete deck. Before the redesign, the bridge carried 5 lanes of traffic and had two 10-foot-wide concrete sidewalks on either side, for a total out-to-out width of 86 feet 6 inches.

    Figure 4. Approach to the bridge showing widened sidewalks.Figure 4. Approach to the bridge showing widened sidewalks.

    In its finished state, the bridge has undergone a road diet to favor pedestrian foot traffic over vehicular traffic. While the out-to-out width remained unchanged, each sidewalk was expanded from 10 feet wide to as much as 21 feet wide. The sidewalks were edged with a 5-foot-wide brick paver strip embedded in the concrete adjacent to granite curbs. Traffic lanes were reduced to three lanes plus two new bicycle lanes. As part of the artwork, the larger of the two sidewalks has a giant aluminum beehive sculpture on a raised dais. At each of the four corners of the bridge, 11-foot-tall aluminum bees greet travelers to their hive from their vantage point on raised plinths tied to the concrete abutments (Figure 4).

    Figure 5. Closeup of beehive lattice at dusk.Figure 5. Closeup of beehive lattice at dusk.

    The spine of the pedestrian enclosure is made up of 138 individual 6-inch x 2-inch x 1⁄4-inch-thick galvanized structural steel tubes evenly spaced at 4 feet on-center. The posts form the rough outline of the pedestrian enclosure shape, with each post varying in length between 3 feet 4 inches to 7 feet 8 inches tall. The posts are all bent inward towards the sidewalks, starting at the same inflection point, creating symmetry at eye level. As the post lengths vary, the end of the frame terminates at different points overhead, creating a dynamic curving and swooping envelope that undulates gradually overhead as one walks from one end of the bridge to the other (Figure 5).

    Figure 6. Schematic of panel connections. Each flat piece of polycarbonate panel (transparent) needs a single co-planar aluminum frame (multicolor) to support it. The frames connect at the edges.Figure 6. Schematic of panel connections. Each flat piece of polycarbonate panel (transparent) needs a single co-planar aluminum frame (multicolor) to support it. The frames connect at the edges.

    Between the steel-post spine is a lattice network of aluminum members arranged into geometric shapes (mostly triangles, with a few quadrilaterals) to support each edge of every half-inch polycarbonate panel (Figure 6). The legs of this lattice consist of a structural angle with a third aluminum fin welded onto it, making a lopsided “T.” The fins were individually measured and custom-welded to control the angle of the fin to the aluminum angle base. This was necessary because each of the three sides of every polycarbonate support frame, made up by three separate aluminum “Ts,” need to be co-planer to flush-mount cleanly behind each piece of polycarbonate. Most of the aluminum frame members support two separate polycarbonate panels, one panel resting along one leg of the main structural angle, and another adjacent piece of polycarbonate along the aluminum fin. Each leg of the support needs to be bent at a slightly different angle to work as a system, with matching sides of the members under the same piece of polycarbonate being always co-planar, while also following the geometry established by the posts of the installation (Figure 5). Significant parametric computer modeling, prototyping, field coordination, and shop work was needed to accomplish this geometric jigsaw. It was imperative to ensure that the panels would each have their required edge supports while still keeping bolt holes within tolerances, both at the polycarbonate panels and the connection points along the spine.

    The bridge is skewed 18 degrees out of perpendicular to the roadway below it and is built along a vertical highway curve, which adds to the geometric complexity of the enclosure. This was a design challenge because, though the two parapets match the vertical curve at the same given point along the highway baseline due to the skew of the bridge, the two pedestrian enclosures on either parapet start and stop at different points along the curve. The net result for fabrication was that no two panels of the bridge were precisely alike. In essence, each panel piece (all 137 panels between the 138 posts) had to be custom manufactured horizontally and vertically to properly fit its exact spot on the bridge deck.

    Creation

    Structurally, the pedestrian enclosure had to be designed for the American Association of State Highway Transportation Officials (AASHTO) Bridge Design Guide’s prescribed loadings, including wind, ice, snow, standard pedestrian loadings, and thermal expansion. Geometry from the architect’s computer model was adjusted to account for the latest measurements of the bridge’s existing shape. The model was fed directly into the structural engineer’s finite element analysis software to confirm the frame’s ability to withstand the required loading. The polycarbonate panels were checked against a wind- and vandalism-type impact loading. Thermal movements were designed to be dissipated over the numerous oversized bolted connections throughout the structure’s lattice.

    The pedestrian enclosure was built on top of reconstructed concrete parapets that were fastened to the existing deck with drilled and epoxied steel dowels. The parapets were built lower than standard to bring the bottom half of the pedestrian enclosure’s shape to eye level and built wider to support the full width of the base plates of the enclosure’s posts. They also conceal several embedded conduits that feed the LED lighting scattered throughout the structure. Paraffin joints, traditional parapet contraction joints coated with paraffin wax, were deliberately spaced to match up with scoring lines in the sidewalk to help blend them into the overall aesthetic.

    The City’s desire for real brick pavers embedded into the concrete deck to match the streetscape on the approaches was unusual for a bridge. The design team accomplished installation by deepening the notch for the bricks to include a drainage mat at the bottom. This mat is rated for pedestrian and tire loads, and is pitched to deposit water out of the paver notch and toward one of several scupper downspouts on the structure.

    A Community Reunited

    The seals on one end of the bridge proudly state, “Do the Impossible.” The public, press, and civic leaders have recognized this project as the significant innovation that it is. The ribbon-cutting ceremony was a huge event, bringing together the project team, City officials, project stakeholders, community groups, families, the press, and residents. The Connecticut Main Street Center advocated and contributed early financing for transit-oriented development in the area. Under construction is Columbus Commons, a $58M mixed-use transit-oriented development with 160 new apartment units, which is a short walk from the Beehive Bridge. City leaders have pointed at an uptick in commercial and residential activity in both of the previously divided neighborhoods, and they anticipate future returns on their investment. The Beehive Bridge is truly a community showpiece that fosters both its people and its infrastructure.■


    | STRUCTURE magazine
    2020.10.02 19:36

    Why and How the Structure Failed

    On March 15, 2018, a pedestrian concrete truss bridge in Miami, FL, collapsed during construction. The span that collapsed had been designed as a concrete truss bridge with prestressed members. Figure 1 shows the bridge site before and after the collapse of the main span. The collapse caused multiple fatalities and raised serious concerns regarding the design and construction of the bridge, including the emerging concept of Accelerated Bridge Construction (ABC). ABC usually involves innovative planning, design, and construction methods to reduce the onsite construction time that occurs when building new bridges or replacing existing bridges. In this project, the main span of the bridge was constructed offsite, then transported and placed onto its piers overnight. The bridge collapsed five days later with the roadway underneath it open to traffic. According to the preliminary report from NTSB, workers were re-tensioning tendons in diagonal member 11 (Figure 1) at the time when the bridge collapsed.

    Figure 1. Main span of the bridge: a) before collapse; b) after collapse. Courtesy of NTSB.Figure 1. Main span of the bridge: a) before collapse; b) after collapse. Courtesy of NTSB.

    The National Transportation Safety Board (NTSB) investigated the collapse and released photographs that showed that the bridge exhibited significant signs of distress before the collapse. Most prominent were cracks in the joint area between diagonal member 11, vertical member 12, and the deck. Forensic material testing showed no significant issues in material strength or quality. An investigation of the bridge deck at the north end showed that reinforcement bars were correctly placed. The NTSB’s final report judged the design of the concrete joint at the north end (between members 11, 12, and the deck) to be flawed and attributed the failure to it. The NTSB investigation also noted that peer-review of the bridge design was rushed, underfunded, and, therefore, more likely inaccurate and incapable of detecting critical design errors.

    Although the NTSB investigation identified the north end joint as the cause for failure, the report was not clear on the specific sequence of processes that led to failure. In this article, a high fidelity computational model was used to develop a forensic understanding of the collapse process. A simulation model of the bridge was created based on the as-built drawings and run on the LS-DYNA platform. The different construction stages were simulated using the model, and parametric studies were carried out to investigate how various influential parameters could have influenced the collapse resistance of the bridge.

    Computational Modeling

    The computational model was constructed using the finite element method, wherein the structure and its components were discretized into a multitude of small elements, each with specific properties associated with its parent material. For example, steel bar elements could yield and fracture, while concrete elements could crush, crack, and exhibit confinement and tension stiffening effects. Tension stiffening is the beneficial effect of reinforcement on the mechanical behavior of surrounding concrete. Prestressing was explicitly accounted for through the introduction of prestressing tendon finite elements. The model was designed to represent member separation and falling of debris to represent the failure process faithfully. Figure 2 shows a schematic of the computational model of the main span of the bridge.

    Figure 2. Simulation setup of the bridge: a) overall computer model of the bridge; b) close-up of reinforcement at the joint; c) steel rebars detailing; d) prestressing tendons detailing.Figure 2. Simulation setup of the bridge: a) overall computer model of the bridge; b) close-up of reinforcement at the joint; c) steel rebars detailing; d) prestressing tendons detailing.

    Numerical Simulation Results

    Before the bridge collapsed, the main span went through four construction stages: prestressing, transportation, relocation, and re-tensioning. The behavior of the structure under each of the stages was simulated using the computational model. The main findings from the simulations are as follows.

    Prestressing Stage

    The simulation results showed that, after releasing the prestressing force in the truss members and deck, localized concrete cracking occurred around the north end joint in accord with the documented damage. At the time, the observed cracks were deemed benign, and additional construction stages were allowed to proceed. These cracks were initial indicators of a serious design problem.

    Transportation Stage

    After assembly on the ground, the main span was transported on two self-propelled modular transporters (SPMTs) and placed onto the piers. The simulation model indicated that the north end joint of the bridge suffered additional minor damage in the concrete adjacent to the prestressing tendon anchor plates for member 11, which were embedded in the deck. This zone was highly stressed due to the confluence of prestressing tendon forces and other bridge member forces. The damage was internal and likely did not manifest as external cracks on the surface of the joint. The computed deflection at the northern end was small, less than 0.12 inches.

    Relocation and Re-tensioning

    Extensive cracking appeared around the joint at the north end of the bridge after the main span was placed on the piers. Figure 3 shows the concrete cracking observed in the real bridge and computed from the simulation model. There is a reasonable correlation between the observation and the simulation, providing confidence in the simulation model’s fidelity. The east side of the joint experienced severe cracking damage in the heel of member 11 (Figure 3a) due to excessive sliding along the cold joint between members 11 and 12 and the deck. Other cracks extended into the deck, creating a pattern consistent with punch-out failure distress associated with the excessive force demand imposed by diagonal member 11 onto the deck. The simulation model suggests that the bridge was on the verge of two different types of failure modes: sliding along the cold joint and punch-out failure in the deck region.

    Figure 3. Cracks in the joint area of Member 11 after relocation: a) actual bridge, courtesy of NTSB; b) simulation.Figure 3. Cracks in the joint area of Member 11 after relocation: a) actual bridge, courtesy of NTSB; b) simulation.

    After observing the cracked condition of the bridge at the north end joint, bridge engineers decided to re-tension diagonal member 11 in an attempt to close the cracks in the joint region. During this operation, the bridge collapsed. The simulation model suggests that collapse occurred due to sliding on the cold joint between members 11, 12, and the deck (Figure 4). In essence, the north end joint was pushed out, causing the bridge to fall off its support. Instead of remedying the cracking symptoms as intended, re-tensioning member 11 aggravated the situation and precipitated the progressive collapse process. Figures 5 and 6, show the collapse process, the final configuration of the actual bridge, and as-computed from the simulation model. The simulation results captured the collapse mode of the bridge reasonably well.

    Figure 4. Sliding action triggered by re-tensioning member 11.Figure 4. Sliding action triggered by re-tensioning member 11.

    Figure 5. Failure mode of the bridge from a) accident video frame, courtesy of Instagram/@o2webdev; and b) computer simulation.Figure 5. Failure mode of the bridge from a) accident video frame, courtesy of Instagram/@o2webdev; and b) computer simulation.

    Figure 6. Close up of failure of member 11 during the collapse: a) simulation; b) accident photo. Courtesy of NTSB.Figure 6. Close up of failure of member 11 during the collapse: a) simulation; b) accident photo. Courtesy of NTSB.

    Parametric Studies

    The simulations clearly showed that the cold-joint design and decision to re-tension were critical factors in the bridge collapse. Parametric studies were conducted using the simulation model to draw broader lessons from the accident to prevent future failures.

    Coefficient of Friction

    The coefficient of friction used in the simulation model was selected as 1.0 based on the as-designed condition of the joint. Since cold joint slip depended on this parameter, the coefficient of friction was increased to 1.4 to see if additional roughening of the cold joint surface could have prevented failure. A coefficient of friction of 1.4 corresponds to an extremely rough surface and represents an extreme value. The simulation showed that, even with this high number, a slip of the joint still occurred and resulted in bridge failure. These results indicate that relying on friction for the stability of the entire structure is risky. Shear keys or some other explicit shear resisting mechanism should have been employed and would have been more reliable and helpful in meeting the horizontal shear demand in the joint.

    Re-tensioning

    Different re-tensioning forces were applied to the tendons in member 11 to reach a stress level that ranged from 55% to 100% of the yield strength of the tendons to study the effect of re-tensioning. The simulation showed that increasing the prestress levels in member 11 led to more damage in the joint area, specifically more heel damage and widespread damage in the body of the joint itself. The simulation clearly showed that increasing the re-tensioning level caused the rate of joint slip to increase significantly. At 95% of the yield strength, the joint quickly slid off the deck. Failure was prevented when the joint was modeled as monolithic (i.e., there was no cold joint).

    Even if member 11 had not been re-tensioned, the bridge would likely have failed as creep exacerbated sliding at the cold joint or punch-out failure. However, since the process would have been slow and entailed widening cracks that serve as a significant warning sign of structural distress, action could have been taken to address the situation. Overall, the simulation results suggest that re-tensioning member 11 should not have been considered as an appropriate solution to reduce the cracking symptoms observed in the cold joint area since it aggravated the sliding of the joint and damaged the integrity of the structure in a catastrophic manner.

    Conclusions and Lessons Learned

    The simulation results showed that cracking damage was initiated as soon as prestressing was applied to the concrete members. After placing the bridge on its supports, severe punch-out cracking patterns developed around the northern joint. The computed damage locations coincided reasonably well with the documented pre-failure crack locations around the cold-joint. The simulation results also suggested that the damaged cold joint at the north end experienced sliding behavior under the re-tensioning forces applied to diagonal member 11, which precipitated the collapse of the bridge. Based on the detailed analysis and simulations, the authors believe that several lessons can be drawn from this accident:

  • A concrete truss with prestressed members supported the collapsed bridge deck. The use of a concrete truss for aesthetic reasons unnecessarily introduced complications related to prestressing and cold joints in the bridge, both of which likely played critical roles in the collapse of the bridge.
  • Relying on friction at a critical joint (between members 11, 12, and the deck) is risky in a non-redundant system like that used in the bridge. Friction is unreliable by nature and can lead to sudden failure when the demand exceeds capacity. Shear keys or some other explicit shear resisting mechanism placed in the cold joints would have been more reliable and helpful in meeting the horizontal shear demand in the joint.
  • Re-tensioning diagonal truss members should not have been considered as an appropriate solution to remedy the cracks in the cold joint area since it promoted more sliding across the cold-joint, making the bridge more vulnerable to collapse. Cracks in the cold joint area should be viewed as a meaningful warning sign of impending collapse, and immediate action should be taken to ensure the stability of the structure after detailed calculations or modeling.
  • The collapse of the bridge does not necessarily imply that accelerated bridge construction is risky. Certainly, it shows the need for adequate analysis simulating construction aspects, such as the presence of cold joints or utility conduits, to ensure the safety of the bridge during and after the construction. Peer review should necessarily be concerned with assessing the impact of such details.
  • The bridge was kept open while it was under construction (member 11 was being re-tensioned), probably to showcase the accelerated construction aspect of the project. This accident reemphasizes the lesson that public safety should never be compromised simply to showcase the application of a new construction technology, even though the technology itself may have been shown to be safe in prior applications. Any construction area is, by nature, hazardous to the public.■
  • References

    Cao, R., El-Tawil, S., Agrawal, A.K., (2020). “Miami Pedestrian Bridge Collapse: A Computational Forensic Analysis” Journal of Bridge Engineering, ASCE. DOI: 10.1061/(ASCE)BE.1943-5592.0001532

    NTSB (2018a). “Preliminary Report: Collapse of Pedestrian Bridge Under Construction Miami, Florida.” www.ntsb.gov/investigations/AccidentReports/Reports/HWY18MH009-prelim.pdf

    NTSB (2018b). “Investigative Update1 (August 09, 2018): Collapse of Pedestrian Bridge Under Construction Miami, Florida”. www.ntsb.gov/investigations/AccidentReports/Reports/HWY18MH009-investigative-update.pdf

    NTSB (2018c). “Investigative Update2 (November 15, 2018): Collapse of Pedestrian Bridge Under Construction Miami, Florida”. www.ntsb.gov/investigations/AccidentReports/Reports/HWY18MH009-investigative-update2.pdf

    NTSB (2019). “Pedestrian Bridge Collapse Over SW 8th Street Miami, Florida March 15, 2018”. Highway Accident Report, NTSB/HAR-19/02.


    | STRUCTURE magazine
    2020.10.02 19:36

    ROW DTLA Building 2

    Envisioned by developer Atlas Capital Group and design architect Rios Clementi Hale Studios, ROW DTLA reinvigorates the vast and historic Alameda Square warehouse and industrial building complex. The project updated the area into a vibrant district of offices, retail, and restaurants, and provides a network of public spaces for live music, entertainment, and festivals in Downtown Los Angeles. Renovated in 2017 under the provisions of the California Historical Building Code (CHBC), ROW DTLA Building 2 is among the first buildings that could be shown to meet the City of Los Angeles’ earthquake hazard reduction requirements for non-ductile concrete buildings per Ordinance No. 183893. The project sets a precedent of how a historic, non-ductile concrete building can be retrofitted without losing its historical nature and visual appeal.

    ROW DTLA Building 2ROW DTLA Building 2

    Building 2 was designed in 1918 by renowned English architect John Parkinson and originally built for the Los Angeles Union Terminal Company. The 400,000 square-foot reinforced concrete building is a significant component of the ROW DTLA development, one of the newest and largest additions to the burgeoning Arts District redevelopment in Downtown LA. Building 2 is approximately 100 feet by 600 feet in plan and consists of six stories with a basement and several rooftop penthouses as well as a rooftop water tower – originally for fire suppression, now maintained as a familiar beacon in the Arts District. New work added a rooftop deck with sweeping, north-west facing views of Downtown Los Angeles, a rare and stunning view of the heart of the city.

    An ownership change in the middle of the project’s design phase was one of the project’s more formidable challenges. The initial owner had directed the Structural Focus team to mimic the retrofit design of a similar building on the campus, a strategy with prominent new moment frames on the exterior, significantly altering the rhythm and proportions of the façade. The new owner had a much different vision for the project, part of which was to maintain the “New York City” feel of narrow streets and formidable building façades – a style incompatible with highly visible retrofit elements. A series of shear wall cores down the center of the long, narrow building was the ideal solution for the new owner’s design vision. The architecture of the rehabilitation fits well with the new design – the building behavior was simplified, and the performance was significantly improved (Figure 1).

    Figure 1. Typical floor plan, showing four new reinforced concrete shear wall cores (blue). Columns highlighted in red received FRP wrapping; typically the outer thirds of the building experienced greater interstory drift due to torsion.Figure 1. Typical floor plan, showing four new reinforced concrete shear wall cores (blue). Columns highlighted in red received FRP wrapping; typically the outer thirds of the building experienced greater interstory drift due to torsion.

    With no dedicated lateral force-resisting system, the building presented challenges and opportunities requiring the structural team to think quickly, adapt to existing conditions, and make the best use of the building’s characteristics. Utilizing ASCE 41, Seismic Evaluation and Retrofit of Existing Buildings, as specified by the Los Angeles ordinance, an ETABS model with existing structural elements was built for understanding the behavior of the historic building and strategically locating the new shear wall additions. With four full-height, specially reinforced concrete shear wall cores, the collection of forces was critical. The team employed the robust and generously reinforced existing beams and slabs, designed to support a historic warehouse live load of 250 pounds per square foot, for double duty in collecting forces in compression, tension, and shear and delivering the load to the new shear walls (Figure 2).

    Figure 2. Detail at the thru-bolt connection between the new shear wall and existing girder. Also showing vertical wall bars passing through cores in the slab.Figure 2. Detail at the thru-bolt connection between the new shear wall and existing girder. Also showing vertical wall bars passing through cores in the slab.

    Because shear wall cores were employed inside the building, the contractor was able to utilize the existing structure for construction staging as they went up the building, largely eliminating the need for extensive scaffolding. Existing beams were attached to new shear walls with thru-bolts, providing easy access and a visible link to the existing structure (Figure 3). Suspecting they would exhibit good behavior, the team performed nonlinear finite element analysis on the existing round, spirally-reinforced concrete columns, and compared their inherent ductility to anticipated building drifts. The goal was to achieve a maximum 2% inter-story drift without inducing a column shear failure. The drift behavior of each column was analyzed by inputting linear and nonlinear properties and axial loads into the MATLAB program CUMBIA, used for force-displacement response of reinforced concrete members under moment. Only columns that could not sustain the imposed drift at the damage control limit were strengthened with Fiber Reinforced Polymer (FRP). This strategy allowed the team to eliminate the need for FRP wrapping on hundreds of sufficiently reinforced concrete columns throughout the building.

    Figure 3. Reinforcement installation at new shear wall core. Note doweling to the existing corner column and force-transfer bolts into the existing girder at the top of the wall.Figure 3. Reinforcement installation at new shear wall core. Note doweling to the existing corner column and force-transfer bolts into the existing girder at the top of the wall.

    The four new shear wall cores required substantial mat foundations which had to be integrated with the existing spread footings. Each original column was supported by a multi-tiered, “wedding-cake” style spread footing. In the original construction, there was evidently no set footing elevation. Rather, crews likely excavated only until competent soil was reached, and that is where each footing went. Since the depth to competent soil varied across the large building footprint, footing elevations varied randomly within an approximately five-foot range. The bottom of the mat sloped to accommodate the varying elevations, always matching the bottom elevation (Figure 4).

    Figure 4. Crews install foundation reinforcement at the bottom of the new mat foundation. Notice “wedding-cake” style original concrete foundations at varying elevations.Figure 4. Crews install foundation reinforcement at the bottom of the new mat foundation. Notice “wedding-cake” style original concrete foundations at varying elevations.

    Since the top of the mat was level, the mat thickness varied as well, while maintaining a required minimum thickness of 60 inches. Several thousand epoxy dowels were required to integrate the existing footings with the new mat system.

    Each shear wall core has a single mat foundation supporting it, with the mat resisting vertical loads, shear loads, and overturning of the core. The structural team worked with the geotechnical engineer to arrive at a rational, allowable bearing value below the mat in the most extreme seismic load cases, permitting settlement greater than typical design allows. This reflected the desired performance level of Collapse Prevention per the CHBC.

    To maintain the early 20th-century charm of the building, engineers carefully surveyed and analyzed the rooftop water tower and façade fire escapes to prove that they could safely remain (Figure 5). With a few suggested upgrades from the team, the water tower sits proudly on top of the finished building; ultimately, however, the five 100-year old fire escapes could not be saved. Untenable strengthening requirements from the City of Los Angeles would have dramatically changed their visual character and proved cost-prohibitive.

    Figure 5. Rooftop water tower elevation from original 1916 Parkinson drawings. Notice support frame is of reinforced concrete.Figure 5. Rooftop water tower elevation from original 1916 Parkinson drawings. Notice support frame is of reinforced concrete.

    The building’s size, age, and countless functionalities presented surprises until the very last days of the project’s construction. Electrical transformers from the early 20th century lined a dark room in the basement; in-floor industrial ovens capped with concrete years ago remained undisturbed, still full of ash and charred concrete; sheet metal spiral chutes used to deliver packages from upper stories down to the loading dock level were found; hidden slab overload damage that previous tenants had attempted to repair was found; and, even windows that had once been above grade were now below the street level with plywood holding back the soil behind them. Design changes and hidden conditions required many unanticipated drawing submittals, bulletins, and addendums.

    Figure 6. Aerial view.Figure 6. Aerial view.

    The $25 million retrofit and adaptive reuse of ROW DTLA Building 2 presented unusual and complex challenges for the design team. However, positive collaboration, flexibility, and adaptability proved key to the project’s successful completion while setting a precedent for the application of the Los Angeles Ordinance No. 183893. ROW DTLA is a considerable part of the revitalization of the Arts District in Los Angeles (Figure 6). Standing as an eclectic and elegant example of adaptive reuse without displacement, ROW demonstrates how maintaining a physical connection to our past is not at odds with a promising economic and cultural future.■


    | STRUCTURE magazine
    2020.10.02 19:36

    Since 2004, there have been 10 hurricanes in the Atlantic Ocean that have each caused over $20 billion in damage. Since the late 1800s, sea levels have risen by 10 inches (250mm) and are expected to continue to rise, according to the National Aeronautics and Scape Administration (NASA). Because of this, Departments of Transportation, transit authorities, and private owners have decided it is necessary to add robustness and reliability to new and existing infrastructure, some of which are over 100 years old. Transportation infrastructure, in particular, is essential, as these weather events sometimes make it necessary to evacuate many people from large areas of the country, and the highway system is the primary evacuation route for most metropolitan areas. Additionally, emergency responders need to be able to move freely, maintaining access to as many areas as possible during and immediately after a storm event.

    Bridges are one of the most vulnerable and critical components of the surface transportation network. A bridge that is out of service in normal conditions can result in long delays and significant detours. What is an inconvenience in normal times can become catastrophic in an emergency.

    Major storm events impart loads on structures in several ways, resulting in varying degrees of damage. Wave action can push and lift the bridge, creating both global lateral and vertical forces. There are additional local impact loads where waves directly strike the bridge. Both flooding and wave action impart a vertical upwards force from buoyancy. The buoyant force can be enough to lift the bridge off its bearings and move it away from its supports. Floods with moving water can push debris against the side of the structure or deposit debris on top, which adds to the gravity loads. Barges and ships break free from their moorings in storm events and can impact bridge superstructures and substructures.

    Most existing bridges were not designed for these additional loads and may not be able to resist them. The best chance of the structure’s survival in the event of an extreme storm is to prevent the structure from being subject to these loads, ideally by ensuring the bottom of the superstructure will be above the highest water or wave level. This is easier to accomplish on a new bridge as the approaching roadway profile can be set to accommodate the necessary bridge elevation. However, it can be difficult on an existing bridge where the travel profile may be set.

    In 2000, Modjeski and Masters raised the Norfolk Southern Shellpot Swing span three feet to keep it out of the flood zone because the machinery used to operate the bridge was frequently flooded from high water events. Normally, a railroad would not be able to take a line out of commission for the time it would take to raise a span. However, this was an unusual situation in that the line was not in use and was being restored. The bridge was floated out on barges, the pier top elevations were increased by three feet, and new bearings were installed. The rehabilitated superstructure was floated back in place and put into service. The bridge has not experienced flood-related damage since.

    While raising the bridge above the flood level is the best method to protect the superstructure, the substructure and foundation will still be subjected to flooding loads, and damage can still occur. Wave action and increased streamflow forces from trapped debris can cause increased loads on piers. Higher water flow velocities increase the likelihood of scour around foundations. Because these issues occur below the waterline, they are not easily or quickly identified. If no monitoring system is present, divers are used to confirm that bridges are safe to continue carrying traffic. However, there is a limited number of qualified underwater inspectors – and immediately after an extreme event, there may not be enough of them to service an area. Bridges that are designed to resist the loads from flood events and increased scour levels are less likely to be damaged. They will be less of a concern, reducing the risk of not having an inspection immediately after an event.

    Movable bridges are used over navigable waterways when the vertical clearance below the bridge is inadequate for the size of the vessels that traverse the channel. This bridge type is particularly vulnerable to flood damage because their profile usually sets them close to the water, and they have sensitive machinery used to operate the bridge. These bridges are opened and closed for marine traffic with machinery that can be on the pier top or inside rooms designed into the piers. These spaces are not watertight once the water elevation is too high. If the machinery is flooded, the bridge will likely not be able to operate until, at minimum, it is repaired and, at worst, completely replaced.

    The Florida Avenue Vertical Lift Bridge in New Orleans was opened to traffic in May of 2005. In August of 2005, the costliest hurricane on record for the United States, Hurricane Katrina, caused $125 billion in damage and over 1,200 deaths. New Orleans was in the direct path of the hurricane and suffered extreme damage. The Florida Avenue Bridge survived the storm, but the electrical operating system was severely damaged. Without a functioning operating system, the bridge could not be raised. This meant the waterway was blocked from allowing emergency supplies to be brought in by water. The US Army Corp of Engineers was prepared to demolish the three-month-old bridge to clear the navigable channel if it could not be made operational. Modjeski and Masters’ engineers were flown in by helicopter to assess the damage and attempt to make the bridge function. After two days of onsite trouble-shooting, the bridge was operating. It was able to be lifted, allowing marine traffic to resume and keeping the new bridge from being destroyed.

    At the time the Florida Avenue Bridge was designed, there was little guidance for engineers to anticipate the types of loads caused by such an event. In 2008, the American Association of State Highway and Transportation Officials (AASHTO) released the Guide Specifications for Bridges Vulnerable to Coastal Storms. The specifications contain guidance for owners and designers on the design of bridges in coastal areas. Methods for calculating wave forces on both substructures and superstructures based on numerical simulations of wave passage under a bridge, including local impact forces, are provided in the guidelines. Physical wave tank tests and numerical simulations were used to develop the Physics-Based Method (PBM), which is used to calculate the forces and verify the results. Bridge failures due to storm surge and wave loading in Gulf Coast states provided field data that was used to verify results.

    Loadings, as outlined in the Guide Specifications, are only one side of the design equation. The engineer must still address the resistance of the structure to the load. Various mitigation methods are used when it is not possible to raise the bridge above flood levels. Some methods can be installed as a retrofit to existing bridges, and others must be incorporated as part of the original design.

    One failure mode observed in previous coastal storms is the unseating of the superstructure due to the combined effects of buoyancy and vertical wave loading. Air trapped in the areas between the beams can also add to the buoyancy effect. To significantly reduce the buoyancy, relatively small and frequently spaced holes that do not affect the structural integrity can be placed in the deck, allowing trapped air to escape. This can be done as a retrofit to existing bridges or as part of a new design. Alternatively, ensuring air can move longitudinally by not using solid diaphragms can also reduce the forces working to unseat the structure. Additionally, effectively tying the superstructure to the substructure through structural means can prevent unseating. However, the vertical loading – including the effects of impact from waves – can be very large and require robust tie-down systems, which may not be practical due to the requirement of the anchorage system placed into the concrete and limited space at the bearings.

    Wave effect substructure.Wave effect substructure.

    In addition to the uplift forces, streamflow and wave effects cause increased horizontal loading. These loads can be high enough to push the bridge laterally off its supports. Lateral restraints at the bearings can be used to resist these forces. These can be added as a retrofit, but it is easier if they are added as part of the initial design. Another option for dealing with lateral loads is to reduce their magnitude by using castellated beams. The large holes designed into the webs of castellated beams create a load path that mimics that of a truss. These large holes significantly reduce the area of the beam, allowing the wave to pass through rather than impact on the surface.

    Wave effect superstructure.Wave effect superstructure.

    Scour is the result of the increased stream flow velocity around bridge piers. Scour results when the flow velocity is high enough to move supporting soil out from under bridge foundations. Scour can occur even under base conditions; however, it is much more likely to occur in a flood event when flow velocity has significantly increased. In new designs, scour depths are predicted based on soil properties and streamflow velocity, which can be selected to reflect an extreme event. The foundation elements are then designed, assuming the scour has occurred. For existing structures that were not designed for scouring, armoring the soils around the piers with riprap can control the impacts. This has been proven to significantly mitigate the risk of scour, even in an extreme flood event.

    Apart from storm events, flooding can also be caused by a tsunami. There are many similarities between the tsunami-generated loadings of structures and coastal storm loading. However, the nature of the waveforms can be very different, which changes the interaction between the structure and wave and results in significant enough differences in structural loading that additional guidelines are needed. Similar to other types of flood load mitigation, raising the superstructure above the top of the expected wave elevation is often the best option for a designer to consider, if at all practical. Efforts are currently underway to develop design guidance based on numerical and experimental studies of tsunami waves and their interaction with bridges for designers and owners considering this unique threat.

    In conclusion, the existing transportation infrastructure – particularly bridges – is susceptible to damage from flooding and high-water events. Measures are being taken to retrofit existing structures and design new structures to make them more likely to survive these impacts. Research is ongoing to help better understand these events. Practicing design engineers should become familiar with published guidance, as part of their due diligence, to provide more robust and reliable designs.■


    | STRUCTURE magazine
    2020.10.02 19:36

    What we had here was a failure to communicate – corrosion engineers found an excellent method to make high-performance coatings stick to steel much better than previous methods. However, nobody talked to the structural engineers to notice that bridge safety was reduced.

    Overlooked as a design problem for decades, grit blasting is the standard process to improve coating adherence to steel surfaces. This process significantly degrades the strength of steel bridges, endangering safe design. In particular, engineers design a bridge, construction and welding are performed, and then construction is inspected and accepted. After acceptance of structural construction, painting staff grit blast steel surfaces and the fatigue limits from cyclic loading that were used in the design are inadvertently altered.

    Figure 1. Grit blasting effects on 4140 steel before thermal sprays (Adapted from K. Padilla, et al.).Figure 1. Grit blasting effects on 4140 steel before thermal sprays (Adapted from K. Padilla, et al.).

    These new fatigue limits provide a lower estimate of the minimum failure stresses required to cause cracks experienced by a bridge due to repeated traffic loads from passing trucks. That is, grit blasting impacts high-speed shards of grit into steel to create a jagged steel surface that significantly reduces the fatigue failure limit (Figure 1) and consequently endangers previous and future designs.

    Figure 2. A fatigue crack is shown on an X-braced bridge, but nearly all cracks start at weld toes (U.S. DOT, Bridge Design Handbook, Design for Fatigue).Figure 2. A fatigue crack is shown on an X-braced bridge, but nearly all cracks start at weld toes (U.S. DOT, Bridge Design Handbook, Design for Fatigue).

    Fatigue Failures of Bridges

    Consider fatigue failures of steel bridges, where fatigue cracking has long been known as a failure problem for bridges. Although corrosion is a contributor to some bridge failures, fatigue is the primary cause. Fatigue cracks occur when a structure is subjected to repeating loads that flex, or stretch, the structure (Figures 2 and 3). Undetected cracks have resulted in the collapse of bridges, and numerous other cracks have been identified and repaired before major bridge damage occurs. In fact, significant industry improvements since the 1960s reduced the number of failures, where biennial inspections and improved inspector training find many cracks in time to make repairs before significant bridge damages occur. Even so, cracks still occur that potentially endanger bridge safety. The goal of this article is to enlighten a recently discovered cause of cracks, i.e., grit blasting fatigue.

    Figure 3. Fatigue crack at the end of a cover plate fillet weld toe (U.S. DOT, Bridge Design Handbook, Design for Fatigue).Figure 3. Fatigue crack at the end of a cover plate fillet weld toe (U.S. DOT, Bridge Design Handbook, Design for Fatigue).

    Testing

    Fatigue curves are necessary to gain a basic understanding of fatigue failures. Extensive research and numerous fatigue tests were performed (J. W. Fisher, et al.) and were published in 1974. Their research – extended by research from others through 1986 – is the basis for the fatigue curves in use today.

    Various design details were tested that are used in bridge design to explain fatigue failures. There are eight design categories, or design details, that include butt welds, stiffener attachments, plate girders, and cover plates (Figure 4).

    Figure 4. AASHTO Fatigue Curves (U.S. DOT, Design and Evaluation of Steel Bridges for Fatigue and Fracture).Figure 4. AASHTO Fatigue Curves (U.S. DOT, Design and Evaluation of Steel Bridges for Fatigue and Fracture).

    Design Rules

    There were numerous important findings during bridge fatigue failure research.

    • All fatigue cracks are initiated at defects or flaws in the steel.
    • The size of the defect does not affect whether or not a crack will occur. Only the presence of a flaw is essential to crack formation.
    • The amplitude, or magnitude, of the changing stress dictates whether a crack occurs or not. The dead load, or constant load due to the weight of the bridge, is not critical to fatigue failures.
    • Nearly all fatigue failures occur at the toes of butt welds and fillet welds, where the sudden change in geometry induces high stresses and occasional microscopic, sharp-pointed valleys caused by welding serve as defects to initiate cracks. This observation is valid for in-service cracks on bridges as well as cracks during fatigue testing.
    • Residual stresses due to heat contractions following welding initiate fatigue cracks.
    • Grinding butt welds to a flat surface profile on steel plates increases the fatigue limit of those welds since the weld toe is eliminated.
    • Slag inclusions or porosity in welds also cause cracking.
    • The slopes for all fatigue curves shown in Figure 4 are the same for any design detail, but the type of design detail dictates the stresses needed to induce cracks.
    • The fatigue limit, or lower limit to cyclic failure, is dependent only on the type of design detail.
    • Each curve is parallel for different types of steel, and only the design detail dictates the curve to be used in the design.
    • The fatigue limit is also referred to as the constant amplitude fatigue threshold (CAFT). In theory, fatigue failure cannot occur if stresses in bridge structures are below the fatigue limit.
    • Although outside the scope of this article, ASME experimental tests of welded piping indicate that fatigue limits do not exist for welded structures. That is, fatigue limits due to applied loads continue to decrease over time, rather than remain constant, as shown in Figure 4.
    • Codes for bridge materials ensure that fracture toughness is adequate to prevent brittle fractures during cold weather.
    • Codes for bridge materials also ensure that surface finishes are controlled at the time of purchase to inhibit fatigue cracks after installation, but grit blasting changes those surfaces after installation.

    Coatings and Grit Blasting

    Consider the processes for high-performance coatings. Many decades ago, paint was commonly used for coatings, but coatings have been remarkably improved in their performance with a wide selection of different coatings. The National Association of Corrosion Engineers and the Society for Protective Coatings (NACE/SSPC) issue several specifications for surface preparations, which include solvent cleaning, hand tool cleaning, water jetting, power tool cleaning, and several grades of sandblasting (Figure 5).

    Figure 5. NACE/SSPC surface finishes, grades of blast cleaning (Adapted from ISO 850-1).Figure 5. NACE/SSPC surface finishes, grades of blast cleaning (Adapted from ISO 850-1).

    When high-performance coatings were first used, shot blasting with rounded particles was a common form of sandblasting. However, shot blasting forms rounded surfaces, which provide poor adherence for coatings. Consequently, grit blasting with jagged particles is commonly used to prepare surfaces to a commercial finish before coating to ensure excellent coating adherence. A near white metal finish is used in saltwater environments. The finished, grit-blasted surface consists of microscopic, sharp-pointed peaks, and depressions. These sharp depressions or valleys act as stress raisers where cracks can initiate.

    Grit Blasting Fatigue Tests

    Test results for 4140 steel are conclusive, and fatigue limits and cycles to failure are significantly reduced by grit blasting steel. In Figure 1, the number of cycles to failure is reduced by an order of magnitude, and the fatigue limit is reduced by 16%. The AASHTO fatigue curves shown in Figure 4 could change significantly if grit blasting was considered. Consequently, predicted fatigue failure stress calculations for repetitive truck loads on bridges could be in error, and bridge safety that is determined during design is affected. That is, bridges are not as safe as intended.

    Even so, few tests have been performed to understand how fatigue properties are affected by grit blasting. There are a few studies on titanium dental implants and a single study on 4140 steel; these tests are all that have been performed.

    Grit Blasting Effects

    Are these 4140 steel test results applicable to bridge design? For the few failures that occur in locations away from welded toes, the answer to this question is simply yes. But the fatigue effects on bridge steels will be more pronounced since bridge steels are softer than 4140 steel.

    For fatigue cracks at weld toes, the answer to this question requires more discussion.

    • As noted, the size of the flaw has a negligible effect on the initiation of fatigue cracks.
    • Microscopic defects at weld toes are typical weld defects that cause cracks.
    • Historically, differences in surface finish reduce fatigue properties, e.g., polished bars are more resistant to fatigue than milled bars of steel.
    • Accordingly, the number of defects on surfaces is the primary contributor to fatigue cracking.
    • Grit blasting creates many more stress impacts at weld toes to reduce fatigue limits and reduce the cycles to failure. That is, more microscopic, sharp-pointed valleys that are created at weld toes increase the probability of cracks.
    • Embedded grit particles in the valleys were observed to be the crack initiation sites during 4140 steel fatigue tests. These particles compounded the stresses at the sharp points of the valleys, and additional embedded particles are expected during the blasting of softer bridge steels.

    In short, grit blasting fatigue reduces the stresses needed to form fatigue cracks, whether on a flange or at a weld. In Figure 4, all of the sloped lines will move downward, and all of the fatigue limits, or CAFTs, will move downward as well. The extent to which these fatigue curves are revised requires further experimental fatigue testing.

    Solutions

    Bridge designs – past, present, and future – are in jeopardy unless fatigue strength reductions due to grit blasting are evaluated for bridge safety. Yes, more research is needed and recommended, but the verdict is evident. Grit blasting reduces fatigue strengths of bridges, and this problem must be addressed to ensure bridge safety. The full effects on bridge safety are not yet known, and earlier accident investigations are also called into question since blasted surface finishes were not evaluated during previous investigations. Grit blasting fatigue (The Leishear Fatigue Stress Theory) is a new tool to troubleshoot bridge failures.

    The problem of grit blasting and fatigue affects multiple industries. The fatigue designs of grit-blasted structures are potentially unsafe for pressure vessels, industrial and municipal piping, cross country oil and gas pipelines, nuclear power plant piping systems, and any other structure or equipment that is designed for fatigue and grit blasted for coating adherence. Much work remains to be done.■

    References

    ASME B31.3-2018, Process Piping, Appendix W, High-Cycle Fatigue Assessment of Piping Systems, ASME Code for Pressure Piping, B31, 2018, American Society of Mechanical Engineers, New York, New York.

    J. Collins, “Failure of Materials in Mechanical Design,” 1993, John Wiley and Sons, New York, New York.

    C. Hinnant, T. Paulin, Experimental Evaluation of the Markl Fatigue Methods and ASME Piping Stress Intensification Factors, 2008, PVP2008-61871, American Society of Mechanical Engineers, New York, New York.

    R. Leishear, Water Hammer and Fatigue Strength Reduction from Grit Blasting for Coatings, 2020, National Association of Corrosion Engineers, Houston, Texas.

    R. Leishear, “Grit Blasting for Coatings Accelerates Piping and Structural Failure,” 2019, Empowering Pumps and Equipment eMagazine, Tuscaloosa, Alabama.

    Load and Resistance Factor Design (LRFD) for Highway Bridge Superstructures, Publication No. FHWA-NHI-15-047, 2007, Revised 2015, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C.

    Steel Bridge Design Handbook, Design for Fatigue, Publication No. FHWA-HIF-16-002–Vol. 12, 2015, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C.

    Design and Evaluation of Steel Bridges for Fatigue and Fracture, Publication No. FHWA-NHI-16-016, 2016, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C.

    Fatigue Strength of Steel Beams With Welded Stiffeners and Attachments, National Cooperative Highway Research Program Report, 147, 1974, National Cooperative Highway Research Program in association with the U.S. Department of Transportation, Federal Highway Administration, Washington, D.C.

    Bridge Fatigue Guide, Design and Details, 1977, American Institute of Steel Construction, Chicago, Illinois.

    K. Padilla, A. Velásquez, J.A. Berríos, E.S. Puchi Cabrera, Fatigue Behavior of a 4140 Steel Coated with a NiMoAl Deposit Applied by HVOF Thermal Spray, Vol. 150, 2002, Elsevier Press, Amsterdam, Netherlands.


    | STRUCTURE magazine
    2020.10.02 19:36

    Bridge Life Cycle Cost Savings

    Standard practice during bridge design and construction is to consider the biddability of the construction documents, the constructability of the design, and the operability of the asset. Quite often, designers do not consider the inspectability of the bridge over its life cycle. Inspection, required by law on a 24-month cycle at a maximum, presents the bridge owner with costs: labor, equipment expenses, travel impacts, and safety. These costs, especially for complex bridges, signature structures, and high-level river crossings, can be reduced if inspectability is included in the design.

    The link between bridge design and inspectability is explored in a paper submitted to the SMT Conference 2010 in New York City, entitled Designing Bridges for Inspectability, by Alampalli and Yannotti, and in an ASCE Technical Note by Mahamid, et al., entitled Structural Design and Inspectability of Highway Bridges. In the Technical Note, the authors conducted a workshop on structural design and inspection of highway bridges at the University of Illinois at Chicago in November of 2017, with participants from state agencies, design and inspection companies, and academics. Both of these sources, as well as other sources such as the FHWA-IF-11-016 Framework for Improving Resilience of Bridge Design, placed a focus on improving current inspection challenges and offered proposed modifications for future design practices, intending to facilitate inspection practice.

    During design, inspectability can be incorporated by improving the ability to inspect the bridge visually. Considering bridge type selection and/or bridge details and providing or improving safe access for inspectors in the design phase is essential. The benefits include improved system preservation because the condition of the bridge can be more accurately monitored, improved safety for inspectors and the public during the performance of the inspection, and overall cost savings from increased inspection efficiency.

    When considering bridge type selection or design of bridge details, the main objective is to increase the visibility to the inspector by avoiding uninspectable elements. This impacts the owner’s ability to monitor and maintain the overall condition of the bridge; because, as noted in FHWA-IF-11-016, “elements that are difficult to inspect are typically problematic to maintain.” Flaws, cracks, and section loss can occur in inaccessible areas behind end diaphragms or between the ends of box or tub girders. Truss members, tie girders, tub girders, or floorbeam cross girders often have areas that are constrained by the member itself. A prestressed concrete box beam bridge is constructed with internal webs that are not visible. These same areas are susceptible to the accumulation of moisture, debris, roadway deicing materials, and other threats that contribute to the deterioration of the steel or concrete and loss of structural integrity. The inability to have visual access to bridge components means that inspectors cannot monitor the condition of these vulnerable areas over time. In turn, the deterioration will not be reported and maintenance will not be performed, presenting a challenge to system preservation and resulting in costly rehabilitation versus planned routine maintenance.

    Wide sidewalks can provide accessibility.Wide sidewalks can provide accessibility.

    Facilitating safe access to the bridge for both inspectors and the public who would be impacted by inspection operations can be accomplished in several ways. One advantage is that improvements to inspection access can be considered at the initial design level or during rehabilitation later in the bridge’s life. On signature or large structures, this can be accomplished by providing catwalks, railings around piers, fall restraint systems, tie-offs on deep girders, and locations where rappelling or traveler systems can be attached to the bridge. A frequently undervalued need is a pull-off or staging area at or under the bridge for safe coordination of inspection operations. For highway structures over roadways, railroads, or waterways, the inspection access considerations are less complicated. Still, even small accommodations can make work safer for inspectors over the life of the bridge. Conversations with experienced bridge inspectors have suggested access improvements such as ensuring an accessible abutment seat height, providing a flat area at the top of slopes to stand or place ladders, locating the girder splices over outer lanes to reduce the need for double lane closures, or making the access hatches to steel tub girders or box floorbeam/cross girders more accessible. Inspection equipment access could also be limited by the width of outboard sidewalks or the placement of high fences and luminaire poles, which may obstruct snoopers, or poor ground conditions underneath the bridge that could be used by manlifts or bucket trucks. There are many factors to consider when looking for ways to optimize inspection access, including reducing or eliminating the need to perform lane closures as much as possible, removing or reducing obstacles to production, improving safety, and allowing inspectors to reach as much of the structure as possible.

    Traveler rail retrofitted to accommodate a scaffold system for inspections.Traveler rail retrofitted to accommodate a scaffold system for inspections.

    Ultimately, the goal is to improve safety and efficiency, which has the potential to realize cost savings over the life of the bridge. While these modifications certainly would improve efforts toward best practices in design, it is possible that cost increases in design or construction would impact their implementation. However, the cost savings over the life of the bridge can potentially outweigh the costs in design or construction. For example, consider the low cost of planning to place tie-offs or to analyze the access to various portions of the bridge during the design phase versus not having these in place in the future. An example is a signature cable-stayed bridge that cost more than $100 million to build in the 1990s, which was constructed without tie-offs on the top of the pylons to facilitate rope access inspection. In another case, a functionally obsolete lift truss bridge with extremely narrow lanes that required overnight inspections was retrofitted with a maintenance traveler. Design solutions can also include reducing or eliminating the use of certain bridge types or details, like prestressed adjacent box beam bridges or diaphragm configurations at abutments that prevent visual inspection of the beam ends or abutment backwall.

    Other solutions include evaluating whether certain areas of a bridge can be accessed by existing equipment configurations (i.e., the largest underbridge inspection vehicle has a 75-foot reach) while in design, and if not, building in methods of access, such as walkways or connections for travelers or rigging. One suggestion in the ASCE Technical Note was an exciting and innovative discussion point regarding the potential use of BrIM as a way to utilize a digital representation to explore the inspectability of a bridge. If the cost of time spent during the design phase to address inspectability is a barrier, perhaps this innovative solution of using BrIM’s agility can help in making inspectability part of best practices in bridge design. Many agency manuals require that designers consider inspectability during the design process, so a strong case can be made for including an actual review of the plans specifically for inspection considerations. Having a bridge inspection specialist who reviews the plans can provide useful suggestions early in the process. Potential solutions may include flat areas adjacent to the abutments or locating the hatches for tub girders in the bottom face of the tub and making them large enough for extension ladders. And, including a discussion on inspection access improvements in a rehabilitation may provide some value if the improvements can be included at that time.

    The downside for not addressing inspectability is the potential increase in the costs of inspections due to equipment and lane closures needed to perform the inspections every 24-month interval for the life of the bridge. Remember, there are also impacts on traffic and safety during inspections. Inspection-friendly alternatives considered early, if possible, can be significant improvements. Safety for inspectors and the traveling public is the overarching benefit that can be realized by designing for improved inspectability, particularly when many solutions can reduce or remove the equipment and lane closure demands. Equipment such as underbridge inspection vehicles and traffic control setups cost money. Impacts to traffic on already congested roadways result in economic costs, through delays to commuters and the trucking industry, not to mention the cost to the environment from the use of fossil fuels and emissions. By providing alternative methods for access to the bridge, perhaps from beneath or by utilizing rigging, travelers, or walkways, the opportunity exists to be safer and more efficient. Any time that the bridge inspection industry can avoid impacting traffic with equipment and subsequent lane closures, both safety and economic benefits are realized.

    As a bridge inspection subject matter expert, the author encourages more thoughtful consideration of inspectability by bridge designers. Our industry should encourage bridge designers to consider the long-term cost savings of improving inspectability and the corresponding improvement in safety for inspectors and the traveling public.■


    | STRUCTURE magazine
    2020.10.02 19:36

    Before the 2016 version of the American Society of Civil Engineer’s ASCE 7 Load Standard, Minimum Design Loads for Buildings and Other Structures, all snowdrifts were two dimensional. The height and width (horizontal extension) of the leeward roof step drifts were taken to be constant all along the roof step. The same holds for windward roof step drifts, parapet wall drifts, and over-the-ridge gable roof drifts. As such, the wind direction of interest was nominally perpendicular to the geometric irregularity, i.e., perpendicular in plan to the roof step, the parapet wall, or the gable roof ridgeline.

    There are some roof geometries where two, 2-D drifts overlap or occupy the same roof area. One such roof geometry is the Northwestern corner of a roof with parapet walls along both the North and West edges. Wind out of the South would result in a two-dimensional drift along the North wall, while wind out of the East would result in a two-dimensional drift along the west wall. Presumably, each of the 2-D drifts would control design for most of the bays along the North and West sides, respectively. The 2-D drift footprints overlap at the corner. Prior to ASCE 7-16, the design snowdrift for the NW corner bay was open to question. Some structural engineers may well have designed the bay for each of the 2-D drifts separately. Other structural engineers may have designed the corner bay for the sum of the two 2-D drifts. ASCE 7-16 clarifies the situation by specifying that the snow depth at any point in the overlap area is taken as the larger of the two 2-D drift depths at that point, as shown in Figure 1. That is, a 3-D drift is not a new drift; instead, it is the drift at locations where well established 2-D drifts overlap.

    Figure 1. Plan view of a 3-D snowdrift at Northwest corner. The dashed line designates the 3-D drift area.Figure 1. Plan view of a 3-D snowdrift at Northwest corner. The dashed line designates the 3-D drift area.

    Note that this approach is consistent with the ASCE 7 approach for roof step drifts. In that case, both the leeward and windward drifts are determined, and the larger (not the sum) is used for design.

    Figure 2. Plan view of 3-D snowdrift for parapet wall at North end wall of gable with N-S ridgeline. The dashed line designates the 3-D drift area.Figure 2. Plan view of 3-D snowdrift for parapet wall at North end wall of gable with N-S ridgeline. The dashed line designates the 3-D drift area.

    Other roof geometries can lead to 3-D snowdrifts, i.e., the overlapping of two 2-D drifts. A simple gable roof, with a N-S ridgeline and a pediment or parapet at the North end wall, is one such example. For wind out of the South, there would be a regular 2-D parapet wall drift, while for wind out of the West, there would be a regular 2-D gable roof drift on the East side of the gable. These two, 2-D drifts would overlap along a portion of the parapet wall East of the ridgeline, as sketched in Figure 2. Extension of the current 3-D drift provision for parapet wall corners and re-entrant corners to other roof geometries is currently under consideration by the ASCE 7-22 committee. One issue is whether such new guidance, which by necessity would increase the length and complexity of the code provisions, is needed.

    As noted above, there is a single wind direction of interest for the 2-D drifts (e.g., nominally perpendicular to the ridgeline for gable roof drifts). However, there are two wind directions of interest for 3-D drifts (e.g., wind out of South and wind out of the East for the Northwest parapet wall corner case discussed above). This raises the question of the likelihood of multiple wind directions in wintertime. For a site with a single, predominant wind direction (e.g., the winter wind is almost always out of the North), the potential for significant 3-D drift formation would seem limited. On the other hand, 3-D drift formation would seem more likely if winter winds from multiple directions were expected. Boston’s 2014-15 winter season was an example of the latter.

    Boston 2015

    Boston and other parts of New England experienced significant losses due to a series of four primary snowstorms in January and February of 2015. Based on an insurance arbitration hearing at which the senior author attended as an expert witness, the incurred losses due to eave ice dams alone were more than $100 million. Table 1 presents a summary of snowfall and wind for each of the four Boston 2015 primary storms.

    Table 1. Snowfall and wind during winter storms in Boston; January thru February, 2015.Table 1. Snowfall and wind during winter storms in Boston; January thru February, 2015.

    The information in Table 1 is based on National Oceanic and Atmospheric Administration (NOAA) Local Climatological Data Sheets for Logan Airport in Boston. It was assumed that snow remained driftable for 3 days after the end of the storm snowfall (i.e., snow from Storm #1 was driftable until 4 AM 1/31/15)(O’Rourke et al., 2005). Furthermore, the wind speed threshold for snow drifting (i.e., wind-induced snow transport) was taken to be 10 miles per hour (mph)(O’Rourke et al., 2005). Hence, for the 114 hours in Storm #1 from the start of snowfall (10 AM 1/26/15) to assumed cessation of drifting (4 AM 1/31/15), drifting was occurring about 68% of the time, assuming the snow source was not depleted.

    The resulting structural damage, in general, and damage to school buildings in particular, triggered deployment of a Federal Emergency Management Agency (FEMA) Building Science Branch assessment team on February 25, 2015. In early March, the FEMA team inspected four partial school collapses – two south of Boston and two in southern New Hampshire. During the FEMA visit, ground snow depth and load samples were taken. The ground snow depths south of Boston ranged from 2.5 to 2.8 feet, and its ground snow loads ranged from 39 to 44 pounds per square foot (psf). The corresponding southern New Hampshire values were 1.4 to 1.7 feet and 22 to 26.5 psf.

    Concerning snow drifting, O’Rourke and Cocca (2018) developed parameters to quantify the influence of wind. Specifically, they recommended that the size (cross-sectional area) of the drift surcharge be a function of the ground snow load and the upwind fetch (as is currently), as well as a winter wind parameter. Two wind parameters were considered. The first, W2, is simply the percentage of time during the winter (October through April) during which the wind speed is 10 mph or higher. Note that there is no particular direction associated with W2; all wind directions can contribute. A direction-specific winter wind parameter, W4, was also considered. The parameter was defined as the largest of the eight values for the percentage of time the wind speed was above 10 mph along each of the eight cardinal directions (N, NW, W…NE). By its nature:

    W2 = W4N + W4NW + … +W4NE

    Table 2. Wind parameters W2 and W4 for the four primary Boston 2015 snowstorms.Table 2. Wind parameters W2 and W4 for the four primary Boston 2015 snowstorms.

    Table 2 presents the W2 and W4 wind parameters for each of the four primary Boston 2015 storms. For example, during Storm #1, and the three days of potential snow drifting that followed, the wind speed was above 10 mph for 68% of the time, while the wind speed in the north nominal wind direction was above 10 mph for 15% of the time.

    Figure 3. Winter wind roses for Boston 2015 storms.Figure 3. Winter wind roses for Boston 2015 storms.

    Figure 3, shows the wind rose for each of the four primary Boston 2015 storms. Note that the winds were predominately out of the Northwest and North, respectively, during Storms #1 and #3. Storm #4 had strong winds out of two directions (NW and W), while Storm #2 had three strong wind directions (N, NW, and W).

    As noted above, wind out of the North and/or West was common in the Boston 2015 storms. Such a wind pattern, for certain roof geometries, results in the formation of 3-D snowdrifts. As described in more detail in the Snow Study Summary Report: Observations of Snow Load Effects on Four School Buildings in New England (FEMA, 2016), which can be downloaded , two of the four roof collapses were due to 3-D snowdrifts at relatively complex roof geometries. At Mitchell Elementary in Bridgewater, MA, the damaging 3-D drift was due to an overlap of a 2-D gable roof drift due to wind out of the North and a 2-D windward roof step drift due to wind out of the West. Similarly, at Plymouth River Elementary in Hingham, MA, the damaging 3-D drift was due to an overlap of a 2-D leeward roof step drift due to a North wind and a 2-D windward roof step drift due to a West wind. The two partial collapses observed in Southern New Hampshire were both regular 2-D drifts at simpler, less complex roof geometries.

    The Boston 2015 wind roses in Figure 3 demonstrated that a shift in wind direction throughout a single snowstorm or over the course of a single winter is possible. The single storm version is common enough that it has been given a name: a Nor’easter. The classic Nor’easter corresponds to a low-pressure system proceeding up the Atlantic coast. In New England, due to the counter-clockwise rotation about a low, there is wind out of the East when the low is south of New York City, followed by wind out of the North when the low is East of Boston. Note that the Boston 2015 wind roses (wind out of the North and West) were not due to a Nor’easter (wind out of the North and East). The Boston 2015 Storm #2 was consistent with a Canadian low traveling along a Southeastern path, somewhat North of Boston.

    The classic Nor’easter and at least one of the Boston 2015 storms established that 90° wind shifts are relatively common in New England. However, this does not establish that such wind shifts are common in other parts of the United States.

    Winter Wind Shift in the U.S.

    As shown above, a wind rose is a convenient way of characterizing wind direction. Figure 4, presents a multiyear rose for Boston, MA. Unlike the individual storm wind roses in Figure 3, the multiyear wind rose in Figure 4 is for 65 winters (October through April). Also, the wind rose in Figure 4 was not restricted to time during and after snowstorms. The multiyear winter wind rose for Boston shows the NW wind was the most common winter direction with W4 = 0.19, and the West wind with W4 = 0.16 was the next most common.

    Figure 4. 65-year winter wind rose for Boston, MA.Figure 4. 65-year winter wind rose for Boston, MA.

    To use multiyear wind roses for locations across the United States, and to quantify the directional variability of the above-the-drifting-threshold-wind, the multiyear wind roses needed to be rotated and normalized. Specifically, each of the multiyear wind roses was rotated so that the predominant snow drifting wind direction (direction of the largest of the 8 multiyear W4 values) was vertical. For Boston, with NW as the predominant direction, the rose was rotated 45° clock-wise (NW direction now “vertical”). All 272 of the multiyear wind roses were then normalized by dividing each of the eight W4 values by the largest for that location. As a result, each of the 272 multiyear wind roses had an amplitude of 1.0 along the vertical, and smaller amounts for all other directions.

    Table 3. W4 values for 272 rotated and normalized wind roses.Table 3. W4 values for 272 rotated and normalized wind roses.

    Table 3 presents the mean, median, minimum, maximum, and standard deviation of the W4 ratios for all possible wind shifts. That is, 90° CW means 90° clockwise from the predominant direction. Notice that the maximum ratio is close to 100% for all wind directions. That is, there were at least one of the 272 locations where W4 for the next most common wind direction was nominally the same as for the predominant or most common direction. Similarly, the minimum ratio was close to 0% for all directions. That is, for at least one of the 272 locations, there was nominally no snowdrift for some direction other than the predominant direction.

    Given the rectilinear nature of most roof geometries, it would seem that a 90° or 270° wind shift from the predominant direction are the two directions of most interest with 3-D drift formation. Assuming a normal distribution, the mean plus 1.5 standard deviations would account for about 93% of the locations. The W4 value for either 90° or 270° CW from the predominate would be (using 0.23 as an average standard deviation for 90° CW and 270° CW)

    (W4)270° = (W4)90° = 0.279 + 1.5(0.23) = 0.62

    It turns out that the drift height is, as a first approximation, proportional to the winter wind parameter. As such, one could argue that at roof areas where the two 2-D drifts overlap, using the larger of 100% of one of the 2-D drift and 60% of the other 2-D drifts is justified.

    Conclusion and Recommendation

    The 2015 Boston case demonstrates that strong winds (capable of causing snow drifting) can change direction during a single storm and over the course of a single winter. The 2015 Boston Winter resulted in 3-D drifts (strong winds from directions 90° apart), which caused partial structural collapses and, in one case, complete closure at one school until the summer.

    Analysis of winter wind across the whole United States indicates that 3-D drifts are not a “Boston-only” phenomenon. Specifically, the analysis shows that a 3-D drift, composed of or based upon 100% of one of the 2-D drifts and about 60% of the others, seems justified.

    It is the author’s opinion that, if the current ASCE 7-16 approach for parapet wall corners is expanded to cover other 3-D drift susceptible roof areas, the 100%/100% approach should be used as opposed to the 100%/60% approach mentioned above. This opinion is based on the following reasoning:

    • The 100%/100% approach is consistent with the current ASCE 7-16 approach for corners (parapet wall and re-entrant) and the long-standing approach for leeward and windward roof step drifts.
    • The 100%/100% approach is easier to use and understand. The 100%/100% approach requires the structural engineer to determine two 2-D drifts and to consider one combination. The 100%/60% approach requires determination of four 2-D drifts (a 100% and a 60% for both directions) and consideration of two combinations (“100%/60%” and “60%/100%).
    • One expects that the number of bays susceptible to 3-D drift formation is small in comparison to the number susceptible to 2-D drift formation. In such situations, “simple and conservative” makes more sense than “complex but precise.”

    Examples of the evaluation of 3-D snow drift using provisions currently in ASCE 7-16 or expected in ASCE 7-22 (i.e., the 100%/100% approach discussed above) are presented in a FEMA guidance document Three-Dimensional Roof Snowdrifts Design Guide (FEMA, 2019), available at .■

    References

    “Analytical Simulation of Snow Drifting Loading,” J. Structural Engineering, ASCE Vol. 131, No. 4, April 2005, (with A. DeGaetano and J. Tokarczyk).

    “Improved Snow Drift Rleations” J. Structural Engrg. May 2019 DOI: 10:1061/(ASCE) St. 1943-541X 0002278, 04019027-1 to 04019027-5 (with J. Cocca)


    | Tervlap
    2020.10.02 19:36

    Az irodaház átadása mellett a fejlesztő kibővített nyilvános zöld felülettel és felújított közterekkel járul hozzá a 13. kerület lakóinak mindennapjaihoz. „Mindazzal, amit a Nordic Light komplexummal, a belső kertben és a projekt körül létrehoztunk, biztosítjuk, hogy az általunk épített környezet az itt élő és dolgozó emberek életére pozitív hatással legyen....


    Replacing a Historic Bridge: Innovative Solutions Add Modern Charm to Grand Avenue Bridge in Des Moines

    Contemplating the replacement of historic structures is never an easy decision for communities to make. Prominent structures have a way of growing into meaningful icons by striking a permanent pose against a city skyline. Unfortunately, the forces of time and weather are relentlessly at work, causing material deterioration to even the best-built structures. Having seasoned professionals involved and engaged, providing critical guidance, is a primary component in the decision-making process. A case in point is the recently completed Grand Avenue Bridge project in Des Moines, Iowa.

    Opened in 1918, the Grand Avenue Bridge was one of a series of four bridges (Locust Street, Walnut Street, Grand Avenue, Court Avenue) built between 1907 and 1918 spanning the Des Moines River in the heart of Iowa’s capital city. Over the years, these ornately-decorated, reinforced-concrete arch structures became symbols of the city’s rich history and are even depicted on the City of Des Moines flag. While these bridges provided passage for horse-drawn carriages, pedestrians, and early automobiles, over decades, the Grand Avenue Bridge, in particular, became a critical link connecting the East Village with the downtown Des Moines business district. By a recent count, approximately 7,600 vehicles utilize it each day, making it one of the most heavily used bridges in the downtown region.

    In the late 1960s, the Locust Street, Walnut Street, and Grand Avenue bridge decks were reconstructed along with other improvements. As a cost-saving measure, most of the original ornamentation was removed, leaving only the arched spans and piers. After another half-decade of use, the time came again in the 2010s to either renovate the existing structures or build entirely new bridges. Focusing on the Grand Avenue Bridge, the professionals with Shuck-Britson were brought on board to help provide guidance in this all-important, reconstruct or replace decision.

    Deteriorated Structure Requires Complete Replacement

    To kick start this process, the bridge experts with Shuck-Britson prepared a structural evaluation report and feasibility study to aid in the repair or replace decision of the century-old arch bridge. The engineering team found the bridge to be structurally deficient with scour-critical concrete piers and immediately set about creating design options for consideration.

    During this phase, multiple public participation opportunities were held to inform the community of the findings, the design process, and receive feedback relating to the design alternatives, schedules, and costs. Shuck-Britson also enlisted the services of Substance Architects to help refine the design concepts. It was determined that renovating the existing bridge would cost between $7 and $10 million but would only result in a short-term solution. Rebuilding a bridge in a similar arch-style could cost more than $30 million. However, a pretensioned, prestressed concrete (PPC) beam bridge would maximize the use of standard construction details and could be constructed for under $9 million.

    Once the decision was made to replace the bridge with a modern concrete beam structure, an Aesthetic Steering Committee consisting of city personnel, architects, and other local stakeholders was established to evaluate the design options and make recommendations to the City Council. Keeping some of the same aesthetic details as the original Grand Avenue Bridge (namely, the iconic arches) was a critical requirement for many of the committee members. To meet this directive, the designers developed a concept that would use scalloped metal panels along the sides of the bridge reminiscent of the original arch span. This design, along with strategically-placed LED accent lighting, would create a new, signature Des Moines River bridge while also satisfying the requirements of efficiency and economy.

    Unique Features, Bridge Details, & Design Challenges

    The new four-span, 446-foot long, 54-foot wide, concrete-beam bridge was designed to support two lanes of traffic, on-street parking, bicycle lanes, and 14-foot wide sidewalks on both sides. A non-standard deck cross-section was incorporated to raise the pedestrian sidewalk above the roadway. A modified crash rail protects pedestrians, while the raised sidewalks with extended overhangs enhance the dramatic effect of the scalloped fascia panels.

    The engineering team also added beamlines under the raised pedestrian sidewalk to support a snooper truck for future under-bridge inspections and maintenance. The additional sidewalk load resulted in nonuniform beam reactions requiring careful analysis to determine the proper reinforcing strand and shear stirrup patterns, as well as bearing pad sizes. Further, more than 30 separate utility conduits were incorporated into or below the new bridge deck.

    Because of existing constraints at the bridge location, several design challenges needed to be addressed to accommodate the preferred bridge design. Foremost was the limited ability to raise the roadway from its current elevation and the preference to avoid changes to the existing floodwalls.

    Since the levee system is critical for protecting the downtown region, there was a strong desire to leave the existing floodwalls and levees intact. Appropriately, the bridge abutments were designed to penetrate the levee on both river banks while still maintaining flood protection for the city, with the new bridge abutments sized to match the locations of the floodwalls. To minimize excavation and disturbance to the existing floodwalls, large portions of the original massive abutments were left in place. The new prototypical, semi-integral abutments were developed to account for the pile fixity caused by the rigid connection/incorporation into the existing abutments.

    Due to the limited ability to raise the roadway, the Shuck-Britson engineers worked closely with the U.S. Army Corps of Engineers (USACE) and the Iowa Department of Natural Resources (DNR) to modify the existing hydraulic model, as well. With the pier footings for the new bridge supported on steel piles extending to bedrock, one less pier was required, increasing the flow area of the river by nearly twenty percent. Additionally, the bridge is designed to withstand the hydraulic effects of a 200-year frequency flood event and the intense water pressure acting against the bridge fascia.

    Expert Coordination & Collaboration Lead to Aggressive Build Schedule

    Following the demolition of the previous structure at the end of 2016, construction began on a new bridge. The shallow river depth allowed for the use of temporary causeways during construction with a minimal impact on the environment.

    All plans were submitted on time, allowing the Iowa Department of Transportation (DOT) to let this comprehensive project on schedule. Shuck-Britson’s estimate of probable cost for the project was $8,612,304.00, with an estimated bridge cost of $7,749,615.00. The actual bid price for the project was $9,060,752.68, with an actual bridge bid cost of $8,379,396.23. The difference in the original cost estimate versus the bid cost is mostly attributed to site difficulties and aesthetic components.

    In November of 2017, a mere 12 months after construction began, the bridge opened to one lane of vehicle traffic in each direction with partial pedestrian traffic. The project was substantially completed in Spring 2018.

    The Shuck-Britson team, along with parent company Snyder & Associates, made the project possible by collaborating to provide the development of project concept statement, preliminary bridge and roadway plans, hydraulic analysis and documentation, final bridge and roadway design plans, as well as the extensive coordination and development of aesthetic details. Also, the design team provided rapid response service for issues that arose during construction. These included addressing unanticipated site conditions, pile driving inquiries, and general construction observation.

    Award-Winning Bridge Project

    The success of the new Grand Avenue Bridge led to a similar design for the Locust Street Bridge location (currently under construction) with plans in the works to let the Walnut Street Bridge in 2022. The innovative aesthetics on the new bridges is viewed as a visual complement to the Iowa Women of Achievement Bridge located just upstream from Grand Avenue and helped to transform the downtown river area for a new generation. Shuck-Britson and their client, the City of Des Moines, were awarded the 2019 Honor Award for Engineering Excellence in the Transportation category by the American Council of Engineering Companies of Iowa (ACEC-IA) for the Grand Avenue Bridge project.

    About Shuck-Britson

    Shuck-Britson specializes as a full-service structural engineering and consulting firm serving clients throughout the Midwest and beyond since 1966. With a focus on diverse client needs, we perform engineering for inspection, evaluation, repair, rehabilitation, strengthening, design, and load rating for all types of bridges and structures.

    After decades of working closely together, Shuck-Britson became part of the Snyder & Associates family in 2008 to deepen and expand the full-service capabilities of both firms. Together we provide extensive civil and structural engineering services grounded in over 90 years of experience. From historic preservation to new construction, Shuck-Britson brings your vision to life through smart, right-sized solutions.

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