Keywords: earthquake response, structural control, bridge design, fluid viscous dampers.

Recent major earthquakes have shown the vulnerability of multi-span bridges at their structural joints where damage associated with pounding and joint unseating has often occurred. Examples of such earthquakes include the 1994 Northridge earthquake and the 1995 Hyogo-Ken Nanbu Kobe earthquake in which over 60% of the bridges within the Kobe metropolitan area were damaged.

A recent approach to mitigate the effect of seismic induced impacts between bridge contiguous frames consists of installing at the structural joints (i.e. expansion joints or abutments) energy dissipation devices such as fluid viscous dampers (FVD) [1]. Such devices are installed either alone or more often in conjunction with seismic cable restrainers [2]. FVDs are able to dissipate a considerable amount of energy relatively to their size, and therefore, are able to reduce relative displacements and velocities of the connected structural components. When activated these devices develop forces that are proportional to the applied velocity raised to an exponent . Both linear (=1) and nonlinear devices (1.0) are currently manufactured and commercially available. In the case of bridge applications often highly nonlinear FVDs (0.5) are preferred over linear devices due to their better efficiency in terms of energy dissipation capacity.

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 inflection points of the intermediate span. In this study the dampers are considered to be installed only in one location, which is the intermediate span expansion joint. The effect of the FVDs is taken into account by using a modified Maxwell type element that consists of a spring and a nonlinear dashpot in line. A set of three ground acceleration time histories recorded during previous major earthquakes is used to carry out this series of nonlinear time history analyses. Previous numerical studies have shown that linear viscous damper can offer a good solution to the problems that arise at the expansion joints of bridges located in seismically active regions [3]. In this paper the performance of linear and linear dampers are compared, where the main objective is to determine an optimal damper size (maximum damper force, F_D and damping coefficient C) but also the best value of damper nonlinearity , among the values selected for this study. Analysis results confirm that FVDs can be effective in improving the overall dynamic behavior of bridge structures and emphasize the better performance of nonlinear dampers. Additional benefits include significant reductions in base-shear forces and longitudinal pier moments.

1

Makris N., Zhang J., "Seismic response analysis of a highway overcrossing equipped with elastomeric bearings and fluid dampers", Journal of Structural Engineering (ASCE), 130(6), 830-845, 2004. doi:10.1061/(ASCE)0733-9445(2004)130:6(830)

2

Saiidi M., Maragakis E., Feng S., "Parameters in bridge restrainer design for seismic retrofit", Journal of Structural Engineering (ASCE), 122(1), 61-68, 1996. doi:10.1061/(ASCE)0733-9445(1996)122:1(61)

3

Feng M., Kim J.M., Shinozuka M., Purasinghe R., "Viscoelastic dampers at expansion joints for seismic protection of bridges", Journal of Bridge Engineering (ASCE), 5(1), 67-74, 2000. doi:10.1061/(ASCE)1084-0702(2000)5:1(67)

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