Improved bridge rating procedures integrating load path redundancy : a cost-effectiveness simulation

McCarthy, Gillian
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University of Delaware
The current economic climate brings increasingly constrained funding for our aging national bridge inventory. Therefore, it is ever more important to those in charge of maintaining this infrastructure to ensure cost-effective asset management. However, current AASHTO bridge rating practice contains arguably an unnecessary degree of inherent conservatism. This is due to the lack of acknowledgement of load path redundancy in current rating practice. This thesis performs a literature review into current rating methodology and discusses where load path redundancy is not and could be accounted for as part of the process. A simulation of adjusted NBI 2010 sufficiency ratings for a set of composite steel girder-concrete deck bridges in the state of Delaware is described. Concurrently, the NBI estimates for the budget required for renewal of those bridges is adjusted to reflect the adjusted sufficiency ratings. These adjustments are done using a number of scenarios which considered parameters such as: the condition of the deck and super-structure and the average time required for those structures to deteriorate by one rating category. The three budgetary scenarios simulated are: No -Change, Deferral of Spending, and Decreased Spending. The results indicate that the proposed changes to the current rating process are cost-effective. The proposed changes are an acknowledgement of load path redundancy by adjusting the way load carrying capacity is rated to be based more on system capacity rather than individual girder capacity and by supplementation of visual ratings with more informed field data. The conclusion is that revising current rating practice to acknowledge load path redundancy affords better prioritization of federal funding and cost-effective asset management as well as the potential for multi-million dollar savings in the state of Delaware. Finally it is acknowledged that while this thesis focuses on the state of Delaware specifically, the hypothesis has the scope to be applied to bridges nationwide.