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29 The results of this section revealed that there have been very State DOT Outsourcing and Private-Sector Utilization (55). few failures of FCBs that were the result of fatigue or fracture. A primary objective of that report was to provide guidance on As discussed chapter two, with the exception of the Silver the outsourcing of major program responsibility of state trans- Bridge (1967) (Figure 1) and the Mianus River Bridge (1983) portation agencies. The outsourcing of the decision-making (Figure 4), no bridges have completely collapsed as a result of process and issues associated with procuring and adminis- brittle fracture caused by fatigue or a flaw in the past 45 years. tering outsourced activities are also discussed. As discussed in chapter two, the failure of the Silver Bridge led to the development and implementation of the national bridge SUMMARY OF RESPONSES TO PART IV-- inspection program in the United States. Interestingly, the fail- RETROFIT PROCEDURES ure of the Mianus River Bridge in 1983 occurred after the implementation of that program. As discussed in chapter two, This section was intended to identify any standard practices however, the failure of the Mianus River Bridge did lead to the that have been developed to improve the redundancy of FCBs. development and implementation of the FCB inspection pro- Approximately 92% of the agencies responding to this ques- gram, which was put into practice in 1988. tion have not developed such policies. As mentioned earlier, respondents were asked to distin- In addition, agencies were asked to identify any research guish between all failures (fracture-critical and non-fracture- needs related to FCBs. A summary of the "yes" votes for each critical) that occurred before and after the implementation of the suggested potential research topics is summarized here. of the FCB inspection program. Unfortunately, many agen- The top three are highlighted in bold. cies did not indicate when the failure occurred. Based on the limited responses, it appears that most were not because the · Develop guidelines related to advanced structural analy- bridge was fracture-critical and could not have been prevented sis procedures to better predict service load behavior in through inspection. Note that this is not to say that FCBs have FCBs (8). not failed catastrophically for reasons such as overloads, scour, · Develop advanced fatigue-life calculation proce- or impact. (A bridge posted for 3 tons that has collapsed dures taking into account the lack of visible cracks because a 30-ton truck attempted to cross it did not fail sim- for FCBs (9). ply because it was fracture-critical.) Rather, the data suggest · Field monitoring for FCBs (10). that there are very few failures that have been caused by · Crack arrest capabilities of bridge steel (3). fatigue or brittle fracture in the absence of overloads, impact, · Establish evaluation procedures for advanced large scour, or corrosion. deformation and member loss (7). · Develop advanced analyses techniques and proce- Owners were asked if any special or formal investigative dures to investigate alternate load paths, redundancy, procedures were implemented when a failure had occurred and bridge collapse (10). to identify the cause of the fracture. Few of the agencies indi- · Develop retrofit procedures to add redundancy (1). cated that any formal procedures exist, although limited inves- tigations were conducted on most failures. In other cases, Although some examples were provided, owners were also the girder was repaired and no formal investigation was asked to suggest other potential research topics. Only a few conducted. Therefore, failure investigations appear to be agencies suggested additional research topics. Three owners conducted at various levels on a case-by-case basis. indicated that inspection frequency and extent for fracture- critical (and all) bridges should be risk-based and related to Another interesting observation from the survey data is ADTT and fatigue details. FCBs on very low ADTT roads related to the lack of owners documenting and archiving should not need the same frequency of inspection as those on reports or data related to failures. Although many failures busy Interstates. Two states indicated that they already con- throughout the United States over the past 30 years are gener- duct inspections as a function of ADTT. For these states, if ally known, interestingly many states did not include these the ADTT is less than 1,000 (150 for the other state), they are failures when replying to this section of the survey. It is not required to perform the detailed inspections associated assumed that the individual who responded had no personal with FCBs. knowledge of the failure or that the individuals who did either did not get the survey, left the organization, or simply forgot. Another potential topic mentioned was that the loading This also implies that not all owners keep a centralized data- of the structure should be checked when investigating the base of failures within their jurisdiction that can be easily potential for collapse. NCHRP Report 406 (34), discussed accessed. Thus, new employees may not be adequately in chapter two, provides a procedure that has been used suc- informed of previous problems on a given structure or when cessfully in practice. One respondent suggested that some a problem previously studied arises. guidance as to the extent of damage, analysis methods, mag- nitude of live load, impact, and so forth, be specified so that The issue of individuals retiring or leaving state DOTs a designer can determine if there is the potential for collapse. was reviewed in NCHRP Synthesis of Highway Practice 313: It should be noted that the 2005 AASHTO LRFD is to have