Effect Of Longitudinal Reinforcement Ratio On Shear Behavior Of Restrained Beams With Web Reinforcement When Shear-Span Ratio Is 1.5

In general, to ensure the final shear failure, a very large longitudinal reinforcement ratio, usually larger than 2.8%, was chosen as a prerequisite in previous studies on shear behavior of reinforced concrete beams. It is very different from that in practice, under such circumstances the longitudinal reinforcement ratio is among 1.0~1.5%. The codified design equations based on such testing data may be unconservative. Systematic investigation for effect of longitudinal reinforcement ratio on shear behavior of RC beams is particularly rare. A majority of previous studies on the effect of longitudinal reinforcement ratio to shear behavior of reinforced concrete members were focusing on ultimate capacity, only a few were engaged in detailed recording of the overall development of cracking and investigation of final failure modes.In this paper, five restrained beams with web and different longitudinal reinforcement were tested under static point loads, with the shear-span ratio being kept around 1.5. On this basis, the overall process of cracking development under shear and the effect of longitudinal reinforcement ratio on it was investigated.At first, development of various cracks carefully recorded and strains on both the rebars and the stirrups were measured in detail, together with the deflections of the beam. In such a way, correlation between the measured strain profiles of the reinforcement and the observed cracking development of each specimen was pursued. Principal factors contributing to the cracking pattern and failure mode were figured out as a result. Secondly, comparison of the tested results unveiled effect of various longitudinal reinforcement ratios on development of cracks, final failure mode, and ultimate capacity. Primary conclusions were thus drawn.Moreover, the measured ultimate shear from the tests were compared with that predicted from China Design Code of Reinforced Concrete structures, GB50010－2002 ,and that from the Response2000,which is based on modified compression field theory by Michael Collins, both were undertaken before the experiments. The experiments showed that the cracking process of such restrained beams in this paper can be divided into three phases, that is, formation of the fanning zones, initialization and development of splitting cracks along longitudinal reinforcement, and accelerating development of the critical crack and/or cracks(diagonal, flexural).During the last two phases, it was observed that further opening of some cracks led to someother cracks stop opening, even closing to some extent. Different amount of longitudinal reinforcement has a significant impact on formation of different cracks. The relationship between the load when the critical diagonal crack appears and the ultimate load is still unclear. As for ultimate shear capacity, the difference between the predicted results obtained from the China Design Code, GB50010－2002, and the tested results is 66%. The results predicted from the Response2000 agrees comparatively well.