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UBC Theses and Dissertations

Performance-based seismic design of post-tensioned concrete columns Zhang, Qi


Bridge structures are critical components of transportation networks. The seismic resistance of bridges not only determines the user safety during earthquakes but also decides the economic recovery of a region after earthquakes. Making bridges earthquake-resistant to provide continuous post earthquake serviceability has been a focus in the industry. In the meantime, accelerated bridge construction is playing an increasingly important role as the construction industry tries to reduce the on-site construction time to minimize traffic interruption. Thus, developing a seismic resilient bridge system becomes a focus of researchers and practicing engineers. To achieve this goal, post-tensioned precast concrete columns in various forms are proposed by researchers. Yet no systematic studies cover various design parameters, which poses difficulty in proposing a design guideline for practicing engineers. This research first presents an overview of the performance-based design methodology and the post-tensioned rocking column system. Based on the literature review and available testing data, preliminary design guidance is developed and further research need is identified. Equations for calculating viscous damping are proposed. Then, this study examines the dynamic behaviors of post-tensioned rigid columns analytically using Lagrange’s method solved with the Fourth-Order Runge-Kutta method. The effects of rocking impacts, tendon stiffness, post-tensioning force, and characteristics of applied loadings on the dynamic behaviors are investigated. Thereafter, finite element models for deformable rocking structures are developed and validated with experimental results. The effect of several factors including concrete strength, post-tensioning force, aspect ratio, axial load ratio, and reinforcement ratio on the seismic performance is presented. Regression analysis is performed to propose equations for calculating the global yielding and stiffness of columns. Under the design philosophy of performance-based design, maximum instantaneous drift-based design criteria are proposed for engineering design. Simplified design charts correlating damage states and drifts are presented to assist in engineering practice. In the end, case studies using fragility analysis are performed to demonstrate the superior performance of the rocking column system compared with traditional reinforced concrete columns.

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