Axial Load Collapse of Reinforced Concrete Columns with Light Transverse Reinforcement

To assess collapse risk of the older reinforced concrete buildings in Iran, six 1/2-scale concrete columns were tested under Quasi-static cyclic loading, simulating earthquake actions along with constant axial forces. Based on the test results, cracking patterns, hysteretic response, shear strength and drift ratio at axial failure of each specimen are presented. Two different failure modes of columns are recognized. The first mode is S-shaped failure pattern, and the second mode is related to a mushroom failure mode. The latter was developed by crushing of the concrete and lacking of longitudinal reinforcing bars. The mushroom failure mode is expected where the axial force is reasonably large. Experimental results of test specimen are compared with ASCE/SEI 41-06 analytical models. It is found that shear strength of columns is estimated reasonably well by ASCE/SEI 41-06 flexure and shear models. However, the predicted ultimate displacement is too conservative and ASCE/SEI 41-06 does not properly predicted failuremechanismof columns.