Fluid viscous damper optimal design for seismic protection of bridges

In bridge structures during strong earthquakes impact as well as intermediate joint unseating can occur when the induced deformations exceed the joint gaps or the joint seat lengths, respectively. Passive dissipation devices such as fluid viscous dampers (FVDs) have been recently used for seismic protection of bridges. These devices are usually installed at the expansion joint or abutment locations and activated by the relative movements of the structural components induced by earthquakes. In this paper the benefits of using FVDs to prevent seismic induced damage in bridges is investigated through a series of finite element time history analyses. The example model used in this study represents a reinforced/prestressed concrete box-girder bridge having five spans and only one expansion joint at one of the infiection points of the intermediate span. The effect of the nonlinear FVDs is taken into account by using a modified Maxwell type element that connects the two independent frames at the structural joint. From the numerical simulation results, an optimal damper degree of non-linearity and damper size are selected so that the structural response is optimized. Analysis results confirm that FVDs can be effective in improving the overall dynamic behavior of bridge structures and emphasize the better performance of nonlinear devices. Additional benefits include significant reductions in base-shear forces and longitudinal pier moments.