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An Engineer Raises Questions About Bridge Deck Structural Integrity

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We would like to commend you for the  excellent and timely article titled Engineers Seek Ways to Warn of Failures ‘Waiting to Happen.' One example where full  disclosure of  information  about  a failure could have  contributed to  better understanding of the  problems  and  might prevent similar errors in the  future  was  orthotropic decks failure on the  Bronx-Whitestone Bridge (2005)  which occurred  within one year after their installation on the bridge. Cracking  already occurred  during testing of the  prototype panels for this project,  however, refined analysis by   experts, having full knowledge of serious fabrication defects of  the test panels, predicted  a “75-year fatigue life” for the  bridge decks. Having been involved in research, development and design of orthotropic deck bridges  over  the past five decades,  we  inquired about specific information  about the extent and  details  of  cracking on the bridge,  however we were advised that this  information was “confidential”. The repairs were very costly and took over a year to  complete.
 
From published information about the prototype panels details, and based on available information about failures of European and  Japanese orthotropic decks,  we  concluded  that  the cause  was not  “the contractors’ fault”, as was implied,  but was due  primarily  to  faulty design,  based on  elastic “fatigue theory”  inapplicable at the welds, while   disregarding  the  much more important effects of  fabrication  (mainly  very large residual tension  forces  caused by excessively  large weld sizes  used  by designers  with the purpose of reducing  the  “stress range” due to  applied truck loading). We advised the AASHTO Bridge Committee and the FHWA about   our conclusions and, as  “Friends of the Committee”, we prepared, as requested by its Chairman,  our  proposed revisions of  design specifications for  orthotropic decks based on pragmatic basis and not on inapplicable academic theory. Our suggestions have been  endorsed  by  several  overseas authorities in this  field, and we presented them with ample corroborating evidence, including  our earlier publications on this subject.  
 
Yet, the FHWA and their engineering consultants decided to prepare the intended second edition of the “Design Manual for  Orthotropic Deck Bridges” based on the  theory  that was demonstrated to be  totally misleading in the BWB  investigation.   (The first, 1963 Edition of the Manual was prepared for the AISC by our office). The FHWA also proposed  their  revisions of the  AASHTO specifications for orthotropic  decks  based  on  analytical approach, which  would  compel  the use  of  unnecessarily  large weld  sizes, thus increasing, rather than  reducing, the decks’ susceptibility to cracking.  The AASHTO Bridge Committee is now  proposing to adopt these  specifications at the coming Committee meeting at  mid-May.
 
 In the meanwhile, during the past year, two versions of orthotropic panels, designed  for redecking of the Verrazano Bridge in New York by similar theoretical methods,  ominously cracked in testing. Again, our requests for specific information on these failures were  denied because of  “confidentiality.” It appears that the costly experiences on the Bronx-Whitestone  Bridge could be  repeated, again, on a much larger scale.     
 
In our publications and messages to the FHWA and the AASHTO  we  insisted that  structural failures should be openly  discussed  in order to draw  proper lessons  from  such cases.  We also recommended mandatory independent reviews  and checking of  major bridge construction and  rehabilitation projects  (as  is  now required in the  U.K),  and pointed out that  such  reviews  could have prevented  many failures, including the 2007   tragic I-35W  bridge collapse in Minnesota (see our  Letter to the Editor, Civil  Engineering, Jan. 2008). This failure was subsequently extensively and openly discussed,  an official NIST report was published, and, eventually,  a cautionary note on design of truss gusset plates was  inserted in the AASHTO LRFD Bridge Specifications.  In our specifications proposal for orthotropic decks we suggested that a similar warning about  the use of  inappropriate analytical approach for  assessment of  their safety  against cracking should be given.   
 
We fully agree with your conclusions that failures offer valuable learning opportunities, and  that  “public safety trumps secrecy.” We trust that, eventually, rational  design and construction rules and specifications for orthotropic decks, in accordance with current state-of-art, will be  adopted.     
 
Roman Wolchuk
Principal, Roman Wolchuk Consulting  Engineers
Jersey  City, N.J
.

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