Residual capacity of RC beams subjected to impact loading: Influence of reinforcement ductility

Reinforced concrete (RC) is commonly used for protectives structures subjected to impulse loading and in the design of such structures, knowledge gained from static load conditions is often used. However, the response of an impulse loaded structural member may be very different compared to a statically loaded one, and hence it is not for sure that the observations made at static loading are also valid when subjected to impulse loading. The aim of this study is to address this uncertainty and compare the residual capacity, in terms of strength and internal work, in RC beams subjected to a combination of impulse and static loads or static load only. The impulse load was generated using a drop weight impact in which tests of 12 beams were carried out, and the residual capacity was subsequently tested statically. In addition, six beams were subjected to static loading only as references. The beams were simply supported with a span length of 1.3 m, cross section of 0.1 x 0.1 m and 2 + 2 phi 6 reinforcement bars of various ductility. Two sets of bars were used: regular bars and prestretched bars; the latter being cold-worked regular bars with increased yield strength but decreased ductility. The drop weight (10 kg or 20 kg) was dropped from a height of 5.0 m and a high-speed camera used to record the beams' response. From the images obtained, Digital Image Correlation technique was used to measure deformations and crack propagation. For pure static loading and mild impact loading (10 kg) combined with static loading, beams with regular bars obtained higher internal work than beams with prestretched bars. However, for severe impact loading (20 kg) combined with static loading, the difference in internal work was negligible. Regardless of bar type, the internal work increased with increased severity of the impact loading.