Study On Shear Behavior Of Reinforced Concrete Shallow Beams Under Different Loading Rates

Concrete and steel bar are typical strain rate sensitive materials.Due to the existence of their strain rate effects,the mechanical performance of the reinforced concrete members under dynamic loads is significantly different from that under static loads.However,the influence of the strain rate effect caused by earthquakes on the bending behavior of the normal section,especially the shear behavior of the inclined section of the reinforced concrete shallow beams has not been clearly explained.Therefore,it is necessary to conduct experimental studies and numerical simulations to analyze the shear behavior of the reinforced concrete shallow beams under various loading rates.In this paper,the shear behavior of four concrete beams without web reinforcement and eight concrete beams with web reinforcement was experimentally studied under four loading rates(0.035 mm/s,3.5 mm/s,35 mm/s,and 350 mm/s).Moreover,two stirrup ratios(0.23%and 0.42%)were designed for the latter.The results showed that the magnitudes of concrete and longitudinal tensile reinforcement are 10-6/s～10-2/s and 10-5/s～10-1/s,respectively,which basically cover the range of the material strain rate generated in an earthquake.For the failure modes of the beams under various loading rates,the shear failure before the yield of the longitudinal tensile reinforcement and the bending shear failure after the yield of the longitudinal tensile reinforcement occurred on the beams without web reinforcement and the beams with web reinforcement of 0.42%stirrup ratio,respectively.For the beams with web reinforcement of 0.23%stirrup ratio,the shear failure before the yield of the longitudinal tensile reinforcement occurred on the beams under static,low and moderate loading rates,while the bending shear failure after the yield of the longitudinal tensile reinforcement occurred on the beams under high loading rates.Furthermore,with the increasing loading rate,the number of bending shear cracks increases and the damage degree of the concrete is more serious.Under the same loading rate,the increase extent of the shear bearing capacity of the beams without web reinforcement is obviously higher than that of the beams with web reinforcement.This is because the strain rate sensitivity of the concrete is higher than the steel bar.In addition,the stain of concrete in the shear-span section increases with the increasing loading rate,but the loading rate does not change the stress status in this zone.The dynamic explicit analysis module of the nonlinear finite element software ABAQUS was used to numerically simulate the shear behavior of the reinforced concrete shallow beams under different loading rates,and the validity of the present model was verified by the existing test data.Afterwards,parameter analyses were performed.The results showed that with the increasing loading rate,the increase in the shear bearing capacity of the beams with low concrete strength,large ratios of shear span to effective depth or small ratio of longitudinal reinforcement is more significant.