UBC Theses and Dissertations
The flexural seismic resistant design of reinforced concrete bridge columns Lara, Otton
Experimental studies about the cyclic response of reinforced concrete bridge columns designed to avoid shear failure and subjected to cyclic, reversible, and increasing displacements have been performed in several laboratories around the world. As a consequence there are several force-displacement relationships, called resultant models, that allow to predict the response of those columns. However, the use of the resultant models for earthquake response requires extensive calibration of several parameters. In this investigation a Finite Fiber Element Model, FFEM, is obtained after calibrating first, the response of 30 circular reinforced concrete bridge columns tested under cyclic, reversible, and increasing displacements. Then a re-calibration is carried out in order to simulate the response of two additional columns shake table tested under two earthquake ground motions. After obtaining satisfactory results the FFEM was used to simulate the seismic response of three bridge columns designed according to the prescriptions of the new seismic design bridge code. The FFEM is able to predict directly four flexural failure mechanisms: cracking and crushing of the unconfined and confined concrete, fracture of the longitudinal steel bars due to tension, P-Δ effects, and fatigue of the longitudinal steel bars. Indirectly, the FFEM is able to predict the possible buckling of the longitudinal bars by capturing the confined concrete strain time-history. In order to capture the low-cyclic fatigue, the FFEM through inelastic dynamic analysis is able to calculate the number of cycles and the amplitude of the cyclic plastic strains so these quantities are introduced into the fatigue equation. The fracture of the bars due to low-cyclic fatigue is a failure mechanism that depends on the accumulation of damage along the severe ground motion. The way to estimate the loss of fatigue life in a steel bar is considering the effect of the duration in the calculations since the materials stress-strain relationships are independent of the duration of the ground motion. In order to determine the accumulation of damage in the bridge column a Cyclic Damage Index is proposed here. The Index is based on the energy dissipated by the column at the end of the ground motion.
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