Cracking of concrete prisms reinforced with multiple bars in tension–the cover effect

Abstract

Cracking effects are the intrinsic attribute of serviceability analysis of reinforced concrete elements. These effects are the research object of numerous studies, which have been carried out for more than half a century. Despite extensive research, there is no commonly accepted methodology for cracking analysis. The existing approaches employ empirical models customised using results of laboratory specimens with simplified geometry that are not able to represent common cracking tendencies adequately. The focus of this experimental study is to examine the influence of the cross-section parameters on the cracking behaviour of concrete elements subjected to tension. The test program encompasses 30 concrete prisms reinforced with multiple bars. Two lengths of the specimens were investigated verifying the comparability of the cracking results of relatively short (500 mm) and long (1210 mm) prisms. All specimens had an identical 150×150 mm cross-section. The number and diameter of bars and cover depth were among the test variables. The bars were distributed in the cross-section ensuring 15 mm, 30 mm, 40 mm and 50 mm depth of concrete cover. The cracking results do not support the generally accepted concept that relates crack widths to crack spacing following which the formation of the maximum crack is expected close to the uncracked block having the maximum length. In the tested specimens, the maximum crack was located next to the uncracked block of maximum length in 60% of the considered prisms; the maximum crack occurred between the two blocks whose sum is maximum in only one case. The adequacy of the crack prediction model from Model Code 2010 was also examined, identifying tendencies that point out potential improvements in the model. The modification should address the evidenced inability of the model to predict the correlation between the cover depth and crack width satisfactorily.