Spalling of concrete cover of cyclically loaded columns and fire behaviour of columns with concrete spalling

Abstract

Fire following an earthquake is a threat to seismically damaged structural members with spalling of concrete cover. To evaluate the fire behaviour of the damaged members, it is important to determine the spalling length and thickness reasonably. In this paper, 16 columns were cyclically loaded to check their concrete cover spalling features. Based on the test results and PEER’s database, formulas are proposed for flexure-critical rectangular columns to approximately evaluate the spalling length and thickness of the columns’ concrete cover. Then, thermal and mechanical performance of the damaged columns in fire is numerically studied. It is found that: (a) the maximum spalling length generally increases with the increasing column’s drift ratio and axial load ratio, but it does not exhibit monotonic trend with the change in the shear span ratio and volumetric transverse reinforcement ratio; (b) the ratio of the equivalent spalling length to the maximum spalling length generally increases with the increasing column’s drift ratio and axial load ratio; and (c) fire endurance of the damaged column calculated using the equivalent model is 7–18% higher than that using the realistic model, and a discounted factor of .8 is recommended for the former.