Analytical and Experimental Investigation of a Controlled Rocking Approach for Seismic Protection of Bridge Steel Truss Piers

Keywords: Seismic design.  Bridges.  Piers.  Seismic resistance.  Steel truss piers.  Controlled rocking piers.  Ground motion.  Seismic response.  Excitation. Longitudinal lateral loads.  Seismic protection.  Seismic performance.

Abstract: A seismic design (or retrofit) strategy allowing uplift and rocking of steel truss piers on their foundation is investigated both analytically and experimentally. To control system response, the use of displacement-based steel yielding devices and velocity-dependant viscous dampers, implemented at the uplifting location, are considered. The devices can be calibrated to capacity protect the existing vulnerable members and the foundation of the structure. The system provides a significant restoring force that can allow re-centering of the structure with proper selection of device properties. The behavior of 2-legged and 4-legged bridge steel truss piers is considered and methods of predicting response under multiple components of seismic excitation are evaluated using nonlinear, inelastic time history analyses. The analytical investigation of seismic response includes ground motions typical of far-field rock sites and near-field ground motions with pulse-type characteristics. Also, the response of 4-legged piers that resist transverse and longitudinal demands in bridges is investigated with three components of ground motion. Experimental investigations include shake table testing of a rocking pier with the added passive energy dissipation devices to verify analytical methods and further investigate the dynamic response. Response quantities of interest include pier displacements, impact velocity, and maximum developed forces.