Experimental Characterization of Metallic Dampers for Seismic Retrofit of Highway Bridges

The seismic effectiveness of metallic dampers as vibration isolators and energy dissipation devices as well as the dynamic performance of high rocker bearings are investigated experimentally. The scope of the study includes optimizing the metallic dampers for maximum dissipation of energy, characterizing full-scale metallic dampers, and understanding the seismic behavior of a small-scale bridge with dampers. Three fullscale dampers, two of straight and one of linearly tapered rods, were fabricated and tested under a progressive cyclic load. Test results consistently show that the tangential stiffness of the metallic dampers does not degrade significantly as the number of loading cycles increases even though slack in the test fixture exists. For practical applications, a 10 percent damping ratio is recommended for the design of metallic dampers composed of straight rods, although a significantly higher ratio can be used for tapered dampers. Finally, a small-scale damper was fabricated and installed in an approximately one-tenth-scale steel-girder bridge model. The model was mounted on a shake table and tested under harmonic and earthquake loads. The test results indicated that the metallic damper is an effective isolator that can prevent energy transmission from the substructure to the superstructure of a bridge. They also show that high rocker bearings are stable even at the table acceleration of 0.54 g (g =9.8 m/s2).