Seismic performance of rectilinearly confined high strength concrete columns

grantor: University of TorontoThe use of high strength concrete (HSC) for structural applications has become widespread in the past two decades. The literature survey conducted revealed that only a limited amount of information is available on the behavior of square HSC columns subjected to earthquake type loads. No experimental study on the seismic performance of rectangular HSC columns was encountered in the literature. As a result, the experimental part of the research program was designed to investigate the performance of square and rectangular HSC columns for ductility and strength. The concrete strength varied between 56 and 112 MPa and the yield stress of the transverse ties varied between 465 and 1402 MPa. First, a performance based confining reinforcement design procedure suggested by Sheikh and Khoury (1997) was calibrated for square HSC columns based on the experimental data reported by Bayrak (1995). An experimental program to investigate the earthquake performance of rectangular columns tested about their strong and weak axes was then carried out. Sixteen HSC columns having 250 x 350 mm cross sections were tested under moderate to high axial load levels and reversed cyclic lateral displacement excursions. Twelve of the columns were tested about their strong axes and four were tested about their weak axes. The effects of concrete strength, reinforcement configuration, amount of lateral reinforcement, axial load level and section geometry were studied. The HSC confinement reinforcement design equations, originally derived based on experimental data from square HSC column tests, were found to be applicable to rectangular HSC columns without any modification when they are used in corroboration with the Equivalent Square Core Concept introduced in this thesis. Based on the experimental observations made during the column tests, the longitudinal reinforcing bar buckling problem was deemed to be an important problem. One of the difficulties encountered in the application of the analytical models to evaluate the column behavior is their inability to predict the failure that is generally initiated by the buckling of longitudinal bars. To investigate this phenomenon an experimental program in which 56 reinforcing bar specimens having different unsupported length to longitudinal bar diameter ratios and initial imperfections were tested. The "Plastic Hinge Analysis Technique" that incorporates reinforcing cage-concrete core interaction and hence the compressive stress-strain behavior of longitudinal bars is presented here.Ph.D