| The nominal strength of reinforced concrete members decreases with the increase of size,and the size effect is obvious.However,due to the limitation of test conditions,the existing research on reinforced concrete members mainly focuses on the medium size and below,and the research on large size specimens is less.Therefore,in this paper,the mechanism of size effect of shear behavior of reinforced concrete members is studied by using three-dimensional rigid body spring method.Based on the research results,the calculation formula of shear bearing capacity is modified,and the corresponding reinforcement measures are put forward.The main contents and conclusions of the study are as follows:（1）The existing researches on the size effect mechanism of shear behavior of reinforced concrete beams are sorted out.The influence of stirrup ratio on the size effect of shear behavior of reinforced concrete deep beams is explored by comparing and analyzing the change trend of shear strength.The results show that the size effect of shear strength of reinforced concrete deep beams is mainly caused by the decrease of shear function provided by arch model shear mechanism,and the influence of beam model shear mechanism is less.On the basis of this study,the influence of through cracks on the size effect of shear behavior of reinforced concrete beams is studied.The results show that for beams with through cracks,the larger the crosssection size,the greater the proportion of shear bearing capacity decline,which is mainly due to the fact that large-sized beams will produce more and wider fine oblique cracks,which aggravate the development of shear oblique cracks,thus hindering the transmission of principal stress of concrete compression bars.（2）Four groups of specimens with different section sizes are designed by using threedimensional rigid body spring element method.The effects of axial compression ratio and shear-span ratio on the size effect of shear behavior of reinforced concrete columns are studied.the mechanism of size effect based on the beam-arch model is analyze;the calculation formula of shear bearing capacity is modified according to the size effect law of Ba（?）ant.The results show that under monotonic load,the shear strength of reinforced concrete columns decreases with the increase of section size,showing obvious size effect,and the increase of axial compression ratio aggravates the size effect.This is mainly caused by the aggravation of the size effect of the concrete shear mechanism in the beam model,and the increase of the shear span ratio slows down the size effect,which is mainly due to the mitigation of the size effect of the concrete shear mechanism in the beam model.According to the simulation data and the influence coefficient proposed by Ba（?）ant’s size effect law,the influence coefficient of size effect on formula calculation can be effectively improved,so that the safety reserve coefficient of shear capacity of large and small size members tends to be consistent.（3）On the basis of monotonic load,the influence of cyclic load on the size effect of shear behavior of reinforced concrete columns is studied.The results show that the increase of axial compression ratio aggravates the size effect under cyclic load,which is mainly caused by the sharp decline of shear mechanism of arch model;the increase of shear span ratio slows down the size effect,which is mainly caused by the alleviation of the downward trend of shear mechanism of arch model.（4）Based on the mechanism of size effect under monotonous and cyclic load,two kinds of reinforcement measures for large size reinforced concrete short columns under high axial compression ratio are put forward,which are steel wire mesh reinforcement and "X" longitudinal reinforcement,respectively.the effects of the two reinforcement measures are compared and analyzed.The results show that compared with the unreinforced column,the deformation performance of the reinforced column is obviously improved,and the degradation rate of shear capacity and stiffness of the reinforced column slows down under cyclic load.at the same time,compared with steel mesh reinforcement,the effect of "X" longitudinal reinforcement is more significant. |
