Modal analysis of long span truss bridges

This paper deals with the analytical and ambient vibration testing studies of the US51 and US41 (both northbound and southbound) bridges. These bridges are long span through-truss type steel bridges crossing the Ohio river in Western Kentucky and located in a region that is influenced by the seismically active New Madrid fault. Seismic evaluation is being carried out because these were built in the early 1940's prior to the implementation of stringent seismic design codes and have not yet been subjected to a large earthquake. The present paper includes the description of bridges, field testing under traffic induced vibrations, three dimensional finite element modeling and calibration with the field test. The results will include the natural frequencies and mode shapes from field testing and finite element modeling.