Squat circular bridge piers under multi-directional seismic attack

Abstract

This thesis presents an experimental investigation of seismic shear behaviour of spirally reinforced concrete circular columns. Sixteen cantilever column specimens, with an aspect ratio of two, were tested under quasi-static multi-directional lateral loading conditions. The main variables studied were the amount of spiral steel content, axial compression load intensity, and displacement history. It was observed that the maximum measured strength, in terms of applied lateral force, appeared to develop at larger ductilities, as axial compression intensity increased. Unless premature shear failure occurred, the ratio of the maximum measured strength of a test column to its ideal flexural strength, computed by the ACI method, was always greater than unity. This strength ratio tended to increase with increasing axial compression load intensity, and decreasing severity of displacement history. For test columns exhibiting moderately ductile or ductile behaviour; the amount of spiral steel content appeared to have no influence on this strength ratio. The onset of strength degradation was delayed as the spiral steel content increased, or when the severity of displacement pattern was reduced. Axial compression increased strength delay. The displacement ductility capacity of test columns was distinctly improved with an increase of spiral steel content. Axial compression tended to increase ductility, whereas, the severity of the imposed regular displacement histories appeared to have minor adverse effects on ductility. Finally, design recommendations on (1) an approach to calculate elastic deformations in reinforced concrete circular cantilever columns, and (2) a seismic shear design proposal taking into account selected levels of displacement ductility demands while also considering effects of imposed inelastic displacement histories, are presented. Good agreement with experimental values was achieved.