Ambient vibration and seismic evaluation of a cantilever truss bridge

An experimental ambient vibration field investigation with a companion computational modeling study of a cantilever truss bridge is presented. The ambient vibration experiments were conducted on the central suspended span and two adjacent anchor spans of the North Grand Island (NGI) Bridge. Three-dimensional finite element model of the bridge is validated against the experimental results. Results from time history analyses using selected ground motions are used to assess the damage threshold of the bridge. A nonlinear static procedure using the capacity-demand spectrum approach is then employed to evaluate the expected seismic performance of the structure. Results show that sway frame members are especially prone to damage under earthquake-induced deformations. However, overall response of the structure may be considered satisfactory from a life safety standpoint.