Seismic retrofit of concrete columns with splice deficiencies by external prestressing.

Abstract

According to the current design practice, reinforced concrete columns should have sufficient ductility to resist major earthquakes. The ductility allows a column to maintain its strength during inelastic response to earthquakes. The research project reported in this thesis involves the use of a new retrofit strategy developed for concrete columns at the University of Ottawa. The new procedure consists of external prestressing existing columns with seven wire strands. External prestressing overcomes diagonal tension caused by shear, confines compression concrete, and may improve the behaviour of spliced reinforcement under reversed cyclic loading. Six large scale bridge columns were built and tested under simulated seismic loading. Four long columns with a circular or a square cross-section of approximately 500 mm, and two short circular columns of 610 mm in diameter, were investigated. The columns all had lap spliced longitudinal reinforcement within the potential plastic hinge region. The splice length was equal to twenty times the bar diameter. The reinforcing details were typical of the pre-1970's design practice. The columns were subjected to a constant axial load of 15% of their concentric capacity. (Abstract shortened by UMI.)