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UBC Theses and Dissertations

Equivalent energy based design procedure for controlled rocking-concentrically braced frames Boddapati, Vinay Kumar


Conventional seismic force resisting systems (SFRSs) such as moment frames, braced frames and shear wall systems rely on the use of ductile design philosophy, where structural components are designed to undergo large inelastic deformations to dissipate the sudden surge of the earthquake energy. This design philosophy has shown to be very effective in preventing structural collapse. However, the extensive inelastic deformation usually leads to significant damage to the structural and non-structural components. Many earthquake reconnaissance reports show that this design philosophy typically leads to residual deformations which result in hefty financial losses. In recent years, novel structural systems, which are targeted to achieve higher performance, have been developed. These structural systems are targeted to resist strong earthquake shaking with minimal structural/non-structural damages. This allows the structure to remain functional immediately after the earthquake. Controlled rocking-concentrically braced frame (CR-CBF) is one such novel system developed to achieve higher performance. CR-CBF relies on the use of post-tensioning (PT) tendons and supplemental damping devices (ED), to create a controlled-rocking mechanism at the base of the structure. Since gravity loads alone cannot eliminate the residual deformations, the PT are introduced in the system to allow self-centering. In addition, ED are installed in the system to dissipate the sudden surge of seismic energy and control the peak displacement response of the structure. Both the PT and ED components are designed to be easily replaceable without affecting the functionality of the structure after a strong earthquake shaking. A novel seismic design methodology named Equivalent-Energy Design Procedure (EEDP) is adopted in this study to design the CR-CBF. This design procedure allows the designers to select different performance objectives at different shaking intensities. Two prototype buildings with varying heights are designed using EEDP. Detailed numerical models of these prototypes are developed in OpenSees (2010) to evaluate the seismic performance of CR-CBF. Detailed performance assessment of the CR-CBFs, in terms of adjusted collapse margin ratio, are evaluated using the FEMA P695 (2009) methodology. The results presented in this thesis demonstrate that the proposed CR-CBFs have adequate earthquake safety and they can be designed efficiently using the proposed EEDP approach.

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