Seismic Performance and Topology Optimization of Building Diaphragms
Fischer, Astrid Winther
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This dissertation investigates the seismic performance of steel deck diaphragms through the effects of rigid and flexible diaphragms on the seismic response, the diaphragm and wall interactions, and the improvements to the diaphragm design using topology optimization. The diaphragm is part of the lateral force resisting system (LFRS), which consists of two main components: the vertical LFRS, i.e., braced frames, shear walls, etc., and the horizontal LFRS, i.e., the diaphragm. With the use of mass-spring models, the diaphragm and wall interactions can be studied, therefore, mass-spring models of a single-story building model and multi-story building models were developed that include a degree of freedom for the diaphragm and two degrees of freedom for the vertical LFRS for each story. The seismic response was studied through a parametric study that considered variations of the diaphragm and wall stiffnesses, mass distribution in the model, and different levels of inelasticity in both the vertical and horizontal LFRS. It was observed that the force demands in both walls and diaphragm(s) depend on the diaphragm and wall stiffness, mass distribution, and the inelasticity levels. Secondly, dynamic amplification occurred in the diaphragm force demands when diaphragm and wall periods are similar. Thirdly, diaphragm forces are observed to be reduced by reducing the capacity of both horizontal and vertical LFRS. Finally, large ductility demands arise in the component of the LFRS with the larger inelasticity level. Three diaphragm examples are optimized for minimum compliance and then modified for a more constructible design. The elastic and inelastic behaviors of modified optimized diaphragm designs were compared to designs using traditional diaphragm design methods. Findings include that the modified designs have stiffer responses in the elastic and inelastic range compared to the traditional diaphragm designs. Furthermore, the modified designs reached a higher capacity at failure and had a better ability to redistribute stresses after initial yield, resulting in a higher amount of dissipated energy through plastic deformations.