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Numerical and experimental investigation of seismic torsional response of single storey ductile structures Dusicka, Peter

Abstract

In a structure's response to earthquake motion, the torsional response in combination with lateral motion can induce detrimental damage to its lateral load resisting system. Structural designers of buildings in seismically active areas generally take advantage of the inelastic behaviour of the structural elements to resist lateral seismic motions, yet the current codes world wide use elastic structural properties as basis for determining the torsional contribution to the response. It is clear that there is a need to better understand the inelastic response of torsionally susceptible structural systems. In response to this need, a collaborative research project between the University of British Columbia and the University of Auckland was initiated in 1998. A number of objectives guided the research, which concentrated on the response of single storey models. The study compared a recently proposed mechanism-based design (MBD) approach, intended for the design of ductile buildings, to the current design building code provisions in Canada and New Zealand. An idealised numerical model was designed for a range of structural characteristics. The design requirements and the response of the models obtained from time history nonlinear dynamic analyses were compared. Several issues were identified in the MBD approach. An investigative numerical study into the significance of strength characteristics, such as strength distribution and the level of design ductility was carried out. Stiffness-to-strength relationships were developed to contrast the response of elastically identical structures, which have the same total base shear capacity, but also have different distribution of strength. The response of models of varying levels of design ductility were also included in the analysis. The influence of various system parameters on the inelastic torsional response was observed. An experimental model was developed and evaluated on the shake table to test the torsional response of ductile structural systems. A number of stiffness and strength eccentric model arrangements were tested into the inelastic range using the University of British Columbia shake table facility. Both uni-directional as well as bi-directional ground motions were used in the experiments. Finally, the response of the shake table model was compared to the response of the idealised model, similar to that used in the numerical analyses.

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