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This paper presents the results obtained from tests of a new friction damping system, which has been proposed in order to improve the response of steel Moment Resisting Frames (MRF) and Braced Moment Resisting Frames (BMRF) during severe earthquakes. The system consists of a mechanism containing brake lining pads introduced at the intersection of frame cross-braces. Seismic tests of a three storey Friction Damped Braced Frame (FDBF) model were performed on an earthquake simulator table. The experimental results are compared with the findings of an inelastic time-history dynamic analysis. The results clearly indicate the superior performance of the FDBF compared to conventional building systems.

SUMMARYValuable insights on the problem of seismic pounding have been obtained recently from analytical studies. So far, the proposed analytical models have not been validated experimentally. This paper presents the results of shake table tests of pounding between adjacent three-and eight-storey single-bay steel framed model structures. The pounding response of the frames was measured for various earthquake intensities and initial separations. The experimental results were compared to the predictions resulting from two existing pounding analysis programs. The solution strategy of the first program, SLAM-2, is based on a modal superposition technique. The second program, PC-ANSR, is a non-linear timestep analysis code in which an elastic gap element has been included. Modelling the pounding effect by elastic gap elements in the two programs produced accurate displacement and impact force results. Amplitudes of short acceleration pulses were not well predicted, however, for practical time-step increments. Relative rotations between adjacent floors induced grinding contacts which cannot be captured by uni-axial gap elements.

In the last decade, many energy dissipating systems have been proposed to raise the seismic design of structures beyond the conventional ductility design approach. Among these new systems, friction damping has shown some great potential. In a friction damped system, friction damping devices are inserted in a structure and slip at a predetermined optimum load during severe seismic excitations, before any yielding of the structural members has occurred. Slipping of the devices allows the structure to dissipate the input seismic energy mechanically by friction rather than by inelastic deformation of the structural elements. This paper presents an overview of the recent research and development in Canada on a particular type of friction damped bracing. Analytical and shake table test results are first summarized to illustrate the earthquake performance of friction damped structures compared to the performance of conventional building systems. The development of a design slip load spectrum for the rapid estimation of the optimum slip load distribution is then presented. Finally, two practical examples of the implementation of this system are described: (1) the design of a reinforced concrete library building; and (2) the retrofit of a precast concrete school building.