Commonly-Used Steel Rods for Cost-Effective Seismic Retrofit of Steel-Girder Bridges: Energy Dissipation and Fatigue Properties

This study was aimed at developing an economical seismic retrofit solution for steel-girder highway bridges in low occurrence seismic zones such as in the Central and Eastern United States. To this endeavor, low-carbon tapered steel rods provided by a local vendor were tested for their ductile behavior, material strength, energy dissipation capacity, and fatigue strength under harmonic and earthquake loads. A full-scale damper made of five tapered rods was then designed for the seismic retrofit of a three-span continuous steel-girder bridge in southeast Missouri; its performance was validated with laboratory tests. The energy dissipated by tapered rods in one cycle was shown nearly independent of loading frequency and specimen size; the corresponding damping ratio rapidly increased at small displacements and approached a value of 0.35~0.40 in the range of over 1.8". Even at a displacement of 2.4", the steel rods survived over 100 cycles of loading with little degradation of their damping property. The five-rod damper fractured in a progressive manner as expected.