Research On Shear Capacity Of High Strength Concrete Beams

Research on shear strength of reinforced concrete beam is one classical issue in basic theory of concrete structure, but there isn't a good theoretical system for shear as the cross section strength due to its complexity of failure mechanism and various influential variables. In the past century, a varity of theoretical formulas have been established by scholars from different viewpoints.However, due to the complexity of these theoretical formulas, it is difficult to be unified and put into practice. Therefore, formula with certain reliability serving as design principle have been proposed in terms of statistical regression analysis based on experimental data by most countries, and China is of no exception. Because China design code (GB50010-2002)is based on experimental results of beams with normal-strength concrete and stirrups, as for beams with high-strength concrete and stirrups, a further study need to be done to determine whether the shear strength could be calculated according to current formula in the code and whether the safety criteria could be satisfied.Now, the ductility of concrete bending members has been emphasized, there has been many researches and made many achivements. But in fact, shear failure is more general, study on ductilityit is very important due to its abrupt and serious consequences.A total of 12 reinforced concrete beams are tested under an energy-absorbing stiff testing facility, and complete load-deflection curves including the post-peak portion, diagonal cracking load, failure load and the longitudinal reinforcement and stirrup strain are obtained. Variables such as concrete strength grade (C30, C60, C80 ), stirrup strength grade (HPB235, HRB400), stirrup ration (0, 0.25%) and the shear span ratio (2.2, 1.5) are considered in this experiment. Failure modes of tested beams mainly include diagonal-tension failure and shear-compression failure.Based on the experimental data, the thesis explores effects of cocrete strength, longitudinal reinforcement ratio, stirrup ratio and shear span ratio on the strength. Through the analysis of the shear ductility, a shear ductility index is proposed.Finally, a new kind of calculation method based on the Softened Strut-and-Tie Truss is established, which can accurately predict the shear strength.