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UBC Theses and Dissertations

Simulation, response sensitivity, and optimization of post-tensioned steel beam-column connections Moradi, Saber


As per current seismic design codes, steel buildings are designed to prevent collapse and loss of lives. Ductile steel structures, however, remain susceptible to earthquake-induced damage. The immediate occupancy of damaged buildings may not be possible. Large permanent deformations can make buildings irreparable and consequently, demolition would be inevitable. For a city with damaged, non-serviceable buildings, the economic losses are significant. Hence, it is crucial to use new techniques to provide self-centering in buildings. A structure with self-centering capabilities can revert to its plumb position following earthquake excitations. As a means of providing self-centering in steel moment-resisting frames, post-tensioned (PT) steel beam-column connections have been proposed and experimentally studied in previous research. Post-tensioning strands are used in parallel to beams to pre-compress the beams against columns. Following an earthquake, the main structural components remain essentially elastic, while the earthquake energy is dissipated by the allocated elements or mechanisms. As a result, permanent damage in a PT frame is substantially mitigated and self-centering is provided. In this PhD dissertation, the lateral load-displacement (or drift) response of PT steel beam-column connections with top-and-seat angles is numerically examined. First, three-dimensional (3D) large-scale finite element models are developed for PT beam-column connections. The simulations are extensively validated with existing experimental results on PT steel connections. The validated simulations are then used to conduct a series of sensitivity analyses. Through a design of experiment methodology, important design parameters affecting the cyclic and monotonic response of PT connections are sequentially identified. The results provide insight into the effects of various parameters with respect to different response variables. Using a response surface method, expressions are developed for predicting response characteristics, such as stiffness, maximum load resistance and ultimate drift capacity of PT connections. Another objective of this research is to optimize the structural response characteristics of PT connections. The optimization problem aims at identifying the regions of design parameters where greater stiffness, strength, and ductility are achieved for PT connections, while minimizing the amount of steel material used in PT connections. The results reveal the factor settings that lead to the optimum conditions.

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