Experimental Study On Shear Mechanism Of Reinforced Concrete Beams With Stirrups

For reinforced concrete beams with stirrups,the shear strength is predicted by summing the shear capacity contribution of concrete and stirrups in GB 50010-2010,JTG 3362-2018,ACI 318-19 and CSA A23.3-14.However,in EN 1992-1-1:2004 and fib Model Code 2010,the contribution of stirrups is considered only and the shear contribution of concrete is ignored,which indicates the inconsistency between the codes.By the way,there has been no accepted calculation method on the shear capacity of concrete in RC beams with stirrups.At present,most studies about shear performance of reinforced concrete beams with web reinforcements are focused on the total shear capacity.There are few studies about the shear capacity of concrete and stirrups in beams with stirrups respectively.For the shear capacity of beams with stirrups,most of the formulas are based on the beams without stirrups.However,it is obvious that the shear capacity of concrete with stirrups and that without stirrups is not equal due to the difference of shear mechanism.Furthermore it may be too conservative or unsafe to use the shear capacity of beams without stirrups.In order to investigate the shear mechanism of reinforced concrete beams with stirrups,this paper is conducted by embedding resistance strain gages into the slotted stirrups to obtain the shear force of concrete and stirrups respectively.Then,the shear behavior tests of 16 simply supported RC beams under concentrated load were performed considering the effect of shear-span ratio,concrete strength and stirrup ratio.To control the high ratio of longitudinal reinforcement,HRB600 steel bar is used as longitudinal tensile steel bar.The test results show that the shear span ratio and the strength of concrete have significant effects on the proportion of the shear force.In particular,when the shear span ratio is relatively small,the stirrups can improve the shear capacity of concrete,but the stirrups bear a little shear force,and even can’t reach their yield strength.When the shear span ratio is relatively large,the inclination angle of the inclined crack is less than 45° and the actual numbers of stirrups intersecting the crack are more than that calculated according to 45° inclined crack,and the shear force contributed by the stirrups increases.Compared with the beams without stirrups,the concrete shear force of a large-span beam with stirrups is reduced.In addition,the rationality of shear components in the theoretical models and the formulas for calculating the shear capacity of different countries are analyzed.Based on the experimental findings in this paper,the experimental data of 369 beams with stirrups are collected and the formulas for calculating the shear capacity of beams with stirrups are obtained by statistical analysis method.The results show that the proposed formula is more reasonable than the current standard（GB50010-2010）and more safe.