The cracking behaviour of reinforced concrete beams under static and dynamic loading

Abstract

Following the 2010 and 2011 earthquakes in Canterbury it was observed that many plastic hinge zones in reinforced concrete beams of multi-story buildings performed unexpectedly. It was seen that a few wide cracks developed, rather than the expected large number of hairline cracks. The purpose of this research was to investigate the effect of different loading types and rates on the cracking pattern in the concrete and strain demand along the reinforcing bar within the plastic hinge zone of a typical beam. This was achieved through conducting tests on concrete prisms simulating the conditions around an individual bar in a beam with typical beam reinforcement content under monotonic and cyclic loading at static and dynamic loading rates. A strain hardness relationship was developed in order to obtain the strains along the reinforcing bar post testing. The results from the static and dynamic tests show that faster rates of loading induce a smaller number of cracks then do static loading rates. There was no observed significant difference between monotonic and cyclic loading. The strain along the reinforcing bar was not uniform and this resulted in concentrated strains developing at crack locations. This research shows that the current strategy of repair of damaged concrete buildings needs to be reconsidered due to this markedly non-uniform strain distribution.