BEHAVIOR AND FATIGUE PROPERTIES OF METALLIC DAMPERS FOR SEISMIC RETROFIT OF HIGHWAY BRIDGES

The objective of this study is to develop an economical solution with metallic dampers for the seismic retrofit of highway bridges in low occurrence seismic zones, such as in the Central and Eastern United States. Select low carbon steel rods were first tested for their ductile behavior and material strength. Large-scale, tapered rods were then tested for their energy dissipation capability and fatigue strength under regular, irregular, and earthquake loads. A full-scale damper made of five tapered rods was designed next for the seismic retrofit of a three-span continuous steel-girder bridge in southeast Missouri; its system performance including joints and connection members was validated with laboratory tests. The damping ratio of tapered rods was shown independent of loading frequency and specimen size; it 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 can survive over 100 cycles of loading with little degradation of their damping property. The full-scale, five-rod damper has been demonstrated to reveal a progressive failure mode that is desirable for earthquake applications. Hysteretic models of Type D rocker bearings were developed for possible consideration in the seismic retrofit design of seismically inadequate highway bridges.