changes in codes, standards and practices following structural failures – part 1

8/20/2019 Changes in Codes, Standards and Practices Following Structural Failures – Part 1

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STRUCTURE magazine December 201016

Changes in Codes, Standards andPractices Following Structural FailuresPart 1: BridgesBy Robert T. Ratay, Ph.D., P.E.

To the credit of our profession, failureshave been and continue to be used toimprove design and construction practices.

We do not just pay up, rebuild and walkaway – we delve, we learn, and we improve.Following a failure, engineers often carry

forensic investigations to great details,so as to have reasonable engineeringcertainty not only in the cause(s) of thefailures but also in the identification ofthe responsible parties – needed for thefrequently inevitable dispute resolution.

A valuable peripheral benefit of the labo-rious search is a clearer understanding ofstructural behavior and a better apprecia-tion of pitfalls in current practices. Thesecan provide information and material toaffect changes in design and/or constructionpractices, codes, standards, oversight andregulatory procedures.The “lessons learned” from failures are

interesting but worthless if not heeded andnot acted upon to prevent their recurrence.Failures of bridges result in reviews and

changes in codes, standards and practicesmuch more frequently than those of build-ings. One reason for this seems to be themore centralized approval and oversightprocesses of bridge construction and main-tenance by state and federal governmentagencies, in comparison to the fragmentedinvolvement of local building departmentsin the approval and oversight of buildingconstruction and maintenance. A bridgecollapse, or even just a temporary closure,affects a large number of people and isquickly picked up by the news media,

while the consequences of the collapse of abuilding seldom reach beyond its occupantsand the local news.

Illustrative Cases

The following are just a few examplesof changes in design and/or constructioncodes, standards, regulations and practicesthat have been initiated in response tostructural failures of bridges.

• Introduction of the NationalBridge Inspection Standards(NBIS) on May 1, 1979, applicableto all structures defined as bridgeslocated on all public roads. Thisstandard directed that each highwaydepartment shall include a bridgeinspection organization capable of

performing inspections, preparingreports, and determining ratings,in accordance with the provisionsof the American Association ofState Highway and TransportationOfficials (AASHTO) Manual for

Maintenance Inspection of Bridges atregular intervals not to exceed twoyears. This mandate followed theDecember 15, 1967 collapse of theU. S. 35 Highway Bridge connectingPoint Pleasant, West Virginia, withKanauga, Ohio (a.k.a. Silver Bridge),caused by the cleavage fracture inthe lower limb of an eyebar in thesuspension chain. Forty-six personsdied, nine were injured, and thirty-one vehicles fell with the bridge.(Figure 1)

• The 1986 publication by theFederal Highway Administration(FHWA) of a manual of inspectio

of fracture-critical bridge memberand widespread retrofitting ofsteel bridge girders with a fail-safeassembly below their pin-and-hanger girder connections. Thisfollowed the June 28, 1983 cleavafracture failure of a pin-and-hangeconnection and catastrophic collaof a highway bridge carryingInterstate 95 over the Mianus Rivin Connecticut. (Figure 2 )

• The Surface Transportation andUniform Relocation Assistance

Act of 1987 expanded bridgeinspection programs to includespecial procedures for the inspectiof underwater components, such piers, of bridges. This followed th

April 3, 1987 collapse of a bridgethe New York State Thruway overthe Schoharie River as a result ofriver-bottom scour. (Figure 3)

• Research and publication ofnew design specifications andconstruction practices for tempora

works by the FHWA and changes

in the provisions for temporary works in the AASHTO StandardSpecifications for Highway BridgeThis followed the 1989 collapseof shoring in the construction ofa highway bridge built to carryMaryland Route 198 over theBaltimore-Washington Expresswainjuring nine workers and fivemotorists, and killing one. (Thiscase is discussed furthered below,because of its role in fueling changin codes, standards and practices.)

• Review of New York State and AASHTO design guides forcomposite tub girders, review ofNew York State Department ofTransportation (NYSDOT) bridgconstruction approval and oversigprocedures, and changes in the N

York State and AASHTO bridgedesign specifications. This followethe October 10, 2002 collapseduring construction of the MarcyPedestrian Bridge in Utica, New Yo(Figure 4 )

Figure 1: Silver Bridge at Point Pleasant,West Virginia.

Figure 2: I-95 Bridge over the Mianus Riverin Connecticut.

Figure 3: New York State Thruway Bridge overthe Schoharie River.


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• Revisions by the Colorado Department ofTransportation (CDOT) to its StandardSpecifications for Road and BridgeConstruction requiring that an erectionplan be developed at least 4 weeks priorto erection of a structural steel member,that a conference be held at least 2 weeksbefore beginning an erection, and thatthe contractor’s Professional Engineerprovide written approval of each phaseof the installation; and, subsequentrecommendations by the NationalTransportation Safety Board (NTSB)to the FHWA, to the Office of Safetyand Health Administration (OSHA),and to AASHTO “to make consistentand compatible [their] organizations’regulatory requirements for and guidance

to construction contractors concerningthe design and certification of falsework,formwork, and bracing for the erectionof highway structures”. This followed theMay 15, 2004 lateral stability failure of afabricated steel girder installed a few hoursearlier for the overpass of Route C-470over Interstate Highway I-70 in Golden,Colorado, killing a family of three in avehicle. (Figure 5 )

• As a result of its extensive investigation,the NTSB made recommendations tothe FHWA and AASHTO regarding,among other things, quality controlprocedures for the design of bridges bybridge design firms, and regarding safetyinspection procedures. This followed the

August 1, 2007 catastrophic collapse,

of an eight-lane 1,900-foot long I-35Whighway bridge over the MississippiRiver in Minneapolis, Minnesota, causby inadequate load capacity, due to adesign error, of gusset plates at a nodeof the main span of the deck truss that

was subjected to loads during roadway work. Four-hundred fifty-six feet of thmain span fell 108 feet into the 15-foodeep river carrying one hundred elevenvehicles. Thirteen people died and onehundred forty five people were injuredThe NTSB also faulted inadequatedesign review by Federal and Statetransportation officials, and the generaaccepted practice at the time amongFederal and State transportation officiaof paying inadequate attention to gussplate distortions during inspections.(Figure 6 )

Figure 4: Marcy Pedestrian Bridge in Utica, NY. Figure 5: I-70 Overpass at Golden, CO.

Figure 6: I-35W Bridge over the Mississippi River

continued on next p



MD Route 198 Bridgeover the Baltimore –

Washington Expressway A highway bridge, built to carry MarylandRoute 198 over the Baltimore-WashingtonExpressway, collapsed during construction onAugust 31, 1989, injuring nine workers and fivemotorists and killing one. The superstructurewas designed as five parallel post-tensioned boxgirders spanning 100 feet between simple-support abutments. The bottom slab of thebox girders was cast in early July and the webswere cast between July 21 and August 4. Onthe day of the collapse, workers were pouringthe 8-inch deck slab. The collapse occurredfive hours into the pour, when 120 of the 160cubic yards total was in place. The shoring col-lapsed “in a flash” without warning, landing allthe formwork and 400 tons of steel and con-crete on the roadway below. (Figures 7, 8 and 9 )The concrete was poured into timber form-

work supported on three simple spans ofparallel steel beams that, in turn, were sup-ported on steel shoring towers placed so as tocreate a 35-foot center span over the roadwayand two 28-foot outboard spans. The form-work shoring (falsework) system was erectedwith a number of changes from the originaldrawings, including the steel beam locations,the deck overhang supports, the concretefoundation slabs below the shoring towers,

and the use of hardwood blocking under thebeams. The formwork shoring had been usedearlier to cast the westbound structure. A forensic investigation by the FHWA andits consultant, T. Y. Lin International, was per-formed, and their findings were presented intheir report (Report of the Investigation into theCollapse of the Route 198 Baltimore-WashingtonParkway Bridge ) on December, 1989. They

evaluated nine possible causes of the collapse,and systematically eliminated all but one.They concluded that the failure originated inone of the shoring towers and the most likelycause was the use of 5-ton screw jacks ratherthan the 12.5-ton screw jacks, shown on theapproved drawings, on the tops of the shoringtowers supporting the bridge. They also notedthat “the top screw jacks were rusty”, thatmuch of the cross-bracing had “large amountsof rust and heavy pitting” and that, in one sec-tion, the cross-brace pieces were connected bynails instead of the required bolts.

Based on the report of the investigators, anFHWA review board concluded that the failureoccurred probably because the shoring towerassemblies were not constructed in accordance

with the approved plans. The review boardfound no evidence that the FHWA (the owner)had not lived up to its contractual responsibil-ities, and ruled that it was the responsibility ofthe contractor to assemble the falsework sys-tem in accordance with the approved design.(It is to be noted that the FHWA did then,and does now, require a contractor’s engineerto certify that falsework has been assembled

according to approved drawings before it isloaded.) As a result, a fine of over $900,000 was levied by the state against the contractor. Additionally, of course, the injured individualsfiled lawsuits of their own.The incident raised increased awareness of

deficiencies in the design-review-approval-execution-inspection process of public roadsand bridges. Several other collapses of bridgetemporary works occurred following the 1989Baltimore-Washington incident, which addedurgency to the need for better guidelines.

Productive Actions after the Failure

The falsework collapse of the Maryland Ro198 bridge over the Baltimore/WashingParkway on August 31, 1989, prompCongress to direct the Secretary of the UDepartment of Transportation to devespecifications and guidelines for use in cstructing bridge temporary works.

This followed the FHWA review boarrecommendation that, in order to prevsimilar occurrences in the future, falsewspecifications should be revised to defimore clearly the responsibilities of matesuppliers, contractors, and engineers. Trecommendation was signed into law by US Department of Transportation and Rela

Agencies Appropriations Bill of Fiscal Y1991, which states in part that “...the Comittee on Appropriations directs the FedHighway Administration to undertake research project recommended in the 19

report entitled Investigation of ConstructFailure Maryland Route No. 198 Bridge Othe Baltimore-Washington Parkway .” The goes on to specify that the research projshould produce approved guidelines, iproved specifications, and a falsework cstruction handbook.In March 1990, the FHWA establishe

multidisciplinary Scaffolding, Shoring, aForming Task Group to develop and guide mandated falsework research program. (Tauthor was a member of that Task GrouThe ensuing activities were described i

September 1991 article (Bridge Temporary WResearch Program) by the FHWA.The FHWA also retained the engineer

firm of Wiss Janney Elstner Associates, I(WJE) to assist the Task Group and,essence, to prepare the Design Specificatiand the Construction Handbook. The eproducts of the Task Group and WJE’s wunder the FHWA’s program were a seriesfive documents: the Synthesis of FalsewoFormwork, and Scaffolding for Highway BrStructures , the Guide Standard Specificat

Figure 7: Baltimore-Washington Parkway. Aerialview of collapse. (From The New York Times,September 1, 1989)

Figure 8: Baltimore-Washington Parkway. Side view of collapse. (From ENR, September 7, 1989)

Figure 9: Baltimore-Washington Parkway. End view ofcollapsed falsework. (From ENR, September 7, 1989)



References1. Report of the Investigation into the Collapse of the Route 198 Baltimore-Washington Parkwa

Bridge , FHWA Publication No. PR-90-001, December 1989

2. Investigation of Construction Failure Maryland Route No. 198 Bridge Over the Baltimore-Washington Parkway , Department of Transportation and Related Agencies AppropriationBill, Senate report No. 101-398, 101st Congress, 2nd Session, 1991

3. Sheila Rimal Duwadi, Bridge Temporary Works Research Program, Public Roads, Septemb1991

4. Synthesis of Falsework, Formwork, and Scaffolding for Highway Bridge Structures , PublicatiNo. FHWA-RD-91-062, June 1992

5. Guide Standard Specification for Bridge Temporary Works , Publication No. FHWA-RD-93-031, November 1993

6. Guide Design Specifications for Bridge Temporary Works , Publication No. FHWA-RD-93-032, June 1993

7. Certification Program for Bridge Temporary Works , Publication No. FHWA-RD-93-033, June 1993

8. Construction Handbook for Bridge Temporary Works , Publication No. FHWA-RD-93-034

August 19939. Bridge Temporary Works , Technical Advisory T5140.24, FHWA, October 29, 1993

10. Standard Specifications for Highway Bridges , 17th Edition, American Association of StateHighway and Transportation Officials (AASHTO), Washington, DC, 200.

11. LRFD Bridge Design Specifications , 4th Edition, American Association of State Highway aTransportation Officials (AASHTO), Washington, D.C., 2007

12. LRFD Bridge Construction Specification, 1st ed. (1998), 2nd ed. (2004), 3rd ed. (2010), American Association of State Highway and Transportation Officials (AASHTO), Washington, DC.

13. Roger Surdahl, Donald Miller, and Vicki Glenn, The Positive Legacy of a Bridge Collapse ,Public Roads, March/April, 2010

Robert T. Ratay, Ph.D., P.E., is a structuralengineer in private practice in Manhasset,NY, and an Adjunct Professor at ColumbiaUniversity. He has been an expert consultanwitness on some 200 cases of structural

problems, some of which resulted in changeof codes, regulations and practices. Dr.Ratay is a Fellow of ASCE, and the Editorof the Handbook of Temporary Structuresin Construction and the Forensic Structura

Engineering Handbook, both publishedby McGraw-Hill. He can be reached [email protected] .

for Bridge Temporary Works, the Guide DesignSpecifications for Bridge Temporary Works, the

Certification Program for Bridge TemporaryWorks , and the Construction Handbook forBridge Temporary Works .

Changes by the FHWA and AASHTOas a Consequence of the Failure

On October 29, 1993, the FHWA issueda Technical Advisory for Bridge TemporaryWorks to the design-construction industryencouraging the use of the four FHWA doc-uments, with the stated purpose “To provideState highway and transportation agencieswith guide standards and design specifications,

a construction handbook and a certificationprogram to assist owner agency and industryperformance in achieving the safe constructionof bridge temporary works. These documentsmay by used in conjunction with Section 3,“Temporary Works, of Division II of the latestedition of the AASHTO Standard Specifica-tions for Highway Bridges.”In Paragraph 1 of its Background section, the

Technical Advisory notes that “Heretofore, therewere [no] national standard code or specifi-cation available on bridge temporary works.The only available national standard which

addressed this type of construction (ANSIA10.9-1983) was applicable primarily forbuilding construction.”Subsequent editions of the AASHTO LRFD

Bridge Design Specifications and the LRFDBridge Construction Specifications adoptedprovisions for temporary works based on theFHWA research program that grew out of the1989 collapse and investigation of the MarylandRoute 198 Bridge over the Baltimore-WashingtonExpressway. Highway bridge specifications ofseveral States followed suit. Review and up-dating of the FHWA documents are presently

underway by the National Cooperative High-way Research Program (NCHRP) as part of itsBridge Construction Practices for TemporaryWorks project.For a detailed discussion of the Maryland Route

198 Bridge over the Baltimore-WashingtonExpressway, including its design and construc-tion, the collapse scenario, and the subsequentinvestigations, the reader is referred to a recentfourteen-page article in Public Roads . (See the listof references included in the online version ofthis article; www.STRUCTUREmag.org .)

Conclusion

Structural failures are the result of humanactivities which, in the design-constructionindustry, are prescribed in part by codes,standards, regulations and industry practices.Therefore, when a structural failure occurs,investigators review the adherence of the failedstructure to the governing codes, standards,regulations and industry practices. If it isfound that those governing documents andpractices contributed to or, indeed, createdthe cause of the failure, then it makes “goodsense” to review those codes, standards, regula-tions and industry practices and, if warranted,to start a process to revise them. The “goodsense” is followed sometimes but not always.The effort is undertaken usually by city, stateor federal agencies with the assistance and talents

of professional societies, trade organizations, avolunteers from private engineering firms a

construction companies.▪

changes in codes, standards and practices following structural failures – part 1

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