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Objective

The primary objective of this research was to investigate the cyclic lateral load performance of unbonded post-tensioned columns. It was critical to determine the effect of the longitudinal reinforcement ratio on re-centering capabilities, and an appropriate initial post-tensioning force that will not yield the tendons at large drift ratios. In addition, the research was used to investigate new and improved construction methods for unbonded post-tensioned concrete columns, specifically developing a constructible full-scale column, including the tendon details. Anchoring the tendons at the corners of the footing was introduced to evaluate the possibility of removing tendons, following a seismic event. The tendons were also greased and sheathed to help protect the strands against corrosion, of which bridges are highly susceptible.
To accomplish these objectives, two columns were constructed and tested under cyclic loading. The columns were constructed side by side, and cast at the same time to ensure similar properties between the two specimens. Throughout testing, strain gauges, displacement transducers, and load cells were used to measure behavior.
An analytical model was developed to determine the column behavior. After the experimental program, the analytical model was updated with the actual material properties. The analytical model proved to be accurate. With an accurate correlation between the measured and calculated results, a parametric study was conducted. The parametric study was used to evaluate a wide range of parameters so design recommendations could be made.