Control of seismic response of bridges by smart dampers

To transfer the braking force due to traffic vehicles, fixed bearings, together with movable bearings, has been commonly used in most bridges in China. From the perspective of seismic consideration, this is an incompatible design in that much larger force and displacement demand may occur for some piers than the others during an earthquake. The piers with fixed bearings would be easier to be damaged than those with movable ones, which was verified by the Wenchuan Earthquake in 2008. This paper proposes an innovative seismic protection scheme of bridges by using MR dampers, mounted in parallel with all the movable bearings. The control design objective is to reduce both the overturning moment of the bridge piers and the displacement of the girder. A clipped-optimal control algorithm is adopted to command the MR dampers, and the command signal can be continuously adjusted instead of bang-bang control. The nominal controller employs LQG control design with the measured forces of MR dampers and accelerations of the pier tops. To better inform the controller about the frequency content of earthquake ground motions, a Kanai-Tajimi shaping filter is used in the controller design. Semi-active control scheme is studied through the comparison with active and passive control strategy. Numerical simulation results considering six earthquakes show that the proposed semi-active control scheme is an effective countermeasure for the seismic protection of the example bridge.