Seismic vulnerability assessment and retrofit recommendations for state highway bridges - case studies




EXECUTIVE SUMMARY

Three Utah state highway bridges were investigated in detail to determine their seismic deficiencies. The bridges were analyzed by different methods recommended in recently published guidelines (FHWA, 2006) that have been evaluated in detail for the state of Utah (Wilson and Ryan, 2009). The bridges were evaluated to an Upper Level ground motion with a no collapse performance objective and a Lower Level ground motion under a serviceability performance objective. A detailed model of each bridge that represents its dynamic behavior was created in LARSA 4D from the bridge plans. The evaluation emphasizes nonlinear analysis to determine the capacities of the existing bridges. Additional computational tools were used to supplement the analyses as necessary. Various retrofit approaches are recommended including seismic isolation, column jacketing, locking motion joints, and using cable restrainers to limit joint separation.


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