Experimental study on the mechanical properties of fire exposed concrete

•Larger reduction of strength in non-transient tests compared to Eurocode.•Two interpretations of strain in non-transient tests.•Larger ultimate strain obtained from non-transient tests than in transient tests.•Transient tests more conservative in terms of strength of fire exposed concrete.•New experimental data in a field of transient tests. A number of fire-induced collapses of concrete buildings has been reported over the last decades, indicating the need of a better understanding of behaviour of concrete during fire events and of reassessing models recommended by currently used standards for structural fire safety design.This study investigates the mechanical properties of concrete exposed to elevated temperatures. After carrying out preliminary compression and temperature tests, ductility and strength of cylindrical concrete specimens at high temperature were measured in transient and non-transient tests. In transient tests, the specimens were preloaded to a certain stress level and heated up to failure. In non-transient tests, specimens were first heated up to a set temperature and then compressed until failure.The results are presented in terms of stress-strain relationships and critical temperatures. Such results are compared with different concrete models found in literature, as well as with the values recommended by the Eurocode (EN, 2004). The analysis of the strength degradation in non-transient tests indicated that strength values recommended by the Eurocode may not be conservative. Similar conclusions were drawn regarding the strain at peak stress, where the values suggested by Eurocode were found to be unrealistic from the design point of view. Based on the comparison of results obtained in transient and non-transient test, more conservative values of the strength were observed in transient tests. More tests are needed, in order to confirm these conclusions on larger data set.