Mitigation of Collapse Risk in Vulnerable Concrete Buildings

Abstract

This study investigates the collapse risk of reinforced concrete building columns constructed prior to the mid-1970's, subjected to cyclic lateral loading. These columns have reinforcement details deemed inadequate by modern seismic design standards, and as such are vulnerable to collapse. Testing of two full-scale, shear-critical column specimens was carried out at the NEES-MAST facility at the University of Minnesota. The test specimens had nominally identical material and reinforcement properties. The primary test variable was the applied axial load, which was held constant for both specimens. The specimens were subjected to increasing lateral displacement cycles until axial load carrying capacity was lost. The thesis discusses the observed lateral and axial load resisting behavior, and analyzes the measured responses of the columns up to and beyond the lateral drift at which they were able to sustain axial load. Test results indicate that column behavior was significantly influenced by the magnitude of the applied axial load, and that the ratio of axial load to gross axial capacity of the longitudinal reinforcement is a key parameter in identifying columns in which axial failure occurs simultaneously with shear failure.