Controlled Rocking Approach for the Seismic Resistance of Structures

An innovative lateral force resisting system is investigated that allows steel braced frames to uplift and rock on their foundation, partially isolating the frame. Passive energy dissipation devices are implemented at the uplifting location to control the rocking response to within allowable limits. The structure’s gravitational forces provide an inherent restoring force during the rocking response that can allow the system to self-center after the excitation ceases. This approach to seismic resistance is investigated here for the seismic retrofit of bridge steel truss piers. Specially detailed, steel yielding devices (buckling-restrained braces) are used as the passive energy dissipation devices in this application. The devices likely require no maintenance and act as ductile structural "fuses" during a seismic event. The static, hysteretic behavior of a steel truss pier is developed first and key design variables identified. The dynamic characteristics of the controlled rocking/energy dissipation system are considered in formulating a capacity design procedure using simplified methods of analysis. An example is provided for the design of a single bridge pier for a specified seismic demand and set of capacity protection limits. An analytical model is developed and nonlinear, inelastic time history analysis is used to verify that the design objectives are met. _____________ Michael POLLINO, Graduate Research Assistant, Multidisciplinary Center for Earthquake Engineering Research, and Ph.D. Candidate, Structural and Earthquake Engineering. The State University of New York at Buffalo, 212 Ketter Hall, Buffalo, NY 14260, USA Michel BRUNEAU, Director, Multidisciplinary Center for Earthquake Engineering Research, and Professor, Dept. of Civil, Structural and Environmental Engineering. The State University of New York at Buffalo, 212 Ketter Hall, Buffalo, NY 14260, USA