Modes of failure of concrete panels exposed to high temperatures

Abstract

Synopsis The occurrence of a mode of general spalling, in which a concrete wall panel or floor slab may be completely destroyed shortly alier the start of a fire test, is examined. Examples are given to suggest that this may be a form of compression failure, caused by strain softening, which has much in common with behaviour observed in a standard compression test. A method of analysis for the structural behaviour of a plain concrete panel is formulated in general terms. This analysis demonstrates the effects of strain softening, suggests that there are two possible modes of instability causing compression failure and shows that instability is not possible under conditions of high axial and flexural restraint. These conclusions are independent of the precise form of the stress-strain relationship but are primarily a direct consequence of the existence of a descending branch in the stress-strain curve of concrete in compression.