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30 substantial additional commentary on how to analyze and · There are two documented collapses of FCBs where the address the loading and analysis issues for FCBs. structure catastrophically failed. One is the Point Pleas- ant Bridge that failed before any initiatives related to The results of the survey also suggest that the applica- the FCP and NBIS. The second is the Mianus River tion of the AASHTO definition of FCMs and FCBs needs Bridge, which failed before the implementation of the clarification, because there is considerable variability in the FCB inspection program. Other failures that were the classification of structures. result of unreasonable overloads should not be directly attributed to the circumstance of the bridge being frac- One owner suggested that research be conducted to eval- ture-critical. Other failures have occurred as a result of uate and identify issues related to overhead sign bridges and scour or impact; but again, these failures are indepen- high-mast lighting towers because these are often fracture- dent of bridge type. critical structures. They further indicated that these structures · There have been several fractures of bridges identified actually give them more problems than bridges; however, as FCBs over the last 30 years that have occurred with- there are no standardized inspection and fabrication specifi- out collapse or resulting in fatality. The apparent ade- cations for these structures. quacy of alternate load paths within all of these structures has provided substantial redundancy, although they were not designed as such. SUMMARY OF SURVEY RESULTS · Owners identified the following as the most important areas for future research related to FCBs: The results of the survey can be summarized as follows: Develop load models, criteria for extent of damage, and guidelines related to advanced structural analy- · Owners use a consistent definition for FCBs that is in sis procedures to better predict service load behavior agreement with that provided by AASHTO. However, in FCBs and the behavior after fracture of an FCM, how they establish which bridges are fracture-critical including dynamic effects from the shock of the frac- is much more variable. A bridge that is determined to ture and, if necessary, large deformations. be fracture-critical in one state may not be identified Develop advanced fatigue-life calculation procedures as such in another state. Often, the decision is based on taking into account a lack of visible cracks for FCBs. engineering judgment. Provide field monitoring for FCBs. · Additional costs associated with the inspection of FCBs Develop rational risk-based criteria for inspection can be considerable, both in terms of direct dollar costs frequency criteria and level of detail based on and the additional indirect costs to the public as a result of ADTT, date of design, and fatigue detail categories lane closures and traffic delays. Most agencies reported present. inspection costs that were 2 to 5 times greater for FCBs Evaluate fracture-critical issues related to sign, signal, than for non-FCBs. Increases in inspection costs of 10 to and light supports. (Respondents indicated that these 50 times have been reported for some structures. structures give them more problems than bridges).