| The flat slab structure of reinforced concrete has been widely used in water conservancy,transportation and civil construction due to its simple structure form,its ability to make full use of the net height space,its good environmental adaptability and its economic and practical advantages.Scholars at home and abroad have done a lot of research on the failure mechanism and the calculation method of ultimate bearing capacity of non-impact cut reinforced concrete slabs,and many achievements have been made.Although it is widely used in engineering,the failure mechanism is not clear and the calculation method of ultimate bearing capacity is not uniform,and the corresponding formulas in domestic and foreign specifications are mostly half theoretical and half empirical.Therefore,it is necessary to further study the punching properties.In this paper,based on the test of anti-punching reinforced concrete slab,the relevant research on its punching performance was carried out,and the corresponding solid model was built by combining the nonlinear finite element software ABAQUS,and the mechanism of hedged cutting failure and the relevant factors affecting the bearing capacity performance were analyzed.The main results are as follows:1.On the basis of the test,the influence rules of concrete strength,anti-punching steel bar（bent steel bar and stirrup bar）and longitudinal steel bar’s anti-cutting failure pattern and ultimate bearing capacity are analyzed and summarized.The test shows that the higher the concrete strength is,the higher the anti-punching strength of the slab is.The shear strength of the plate increases with the increase of the reinforcement ratio,but the increase is not as large as that of the reinforcement ratio.When the reinforcement ratio of the longitudinal reinforcement reaches 2.2%,the shear strength of the plate does not increase significantly.2.By using the nonlinear finite element software ABAQUS and the selected plastic damage model of concrete and the corresponding constitutive relationship,the finite element solid model of the reinforced concrete slab with anti-punching is further established,and the finite element analysis of the reinforced concrete slab with anti-punching is carried out.The load-deflection curve and the corresponding stress cloud map obtained by simulating the whole process from test loading to failure are in good agreement with the test results.The model is used to analyze the concrete strength,longitudinal reinforcement and anti-punching reinforcement.It is concluded that the ultimate bearing capacity is linearly correlated with the concrete strength whether or not the anti-punching reinforcement is installed in the concrete slab.The ultimate bearing capacity of non-impact reinforced concrete slab increases with the increase of longitudinal reinforcement ratio,which is approximately linear with the increase of longitudinal reinforcement ratiothe reinforced concrete slab with anti-punching shear,the approximate linear correlation with?（0.3）To eliminate the influence of other factors,the ultimate anti-punching bearing capacity is positively correlated with the bearing capacity of the anti-punching steel bar（As fy）,but there is a certain upper limit for the amount of reinforcement of the anti-punching steel bar.3.Based on the experimental results and the finite element analysis results of the research group,the ultimate bearing capacity of the reinforced concrete slabs with anti-punching is divided into three parts:the bearing capacity of concrete items,the bearing capacity of longitudinal reinforcing bars and the bearing capacity of anti-punching reinforced concrete slabs.On the basis of this,by using the unified strength theory of concrete with three parameters and the limit equilibrium method,the corresponding calculation formula of the limit bearing capacity of concrete against impact is put forward.4 Combined with domestic and foreign configuration of reinforced concrete slab to shear test data,the comparison of the formula in this paper,the hydraulic concrete structure design code（DL/T5057-2009）,design code of concrete structure（GB50010-2010）,American standard（ACI318-2014）,European standard specification（EN1992-1:2004）and Russia（CΠ52-101-2003）configured in the punching shear resistance of reinforced concrete plate related parameters in the formula of the difference and the calculation results with the test results conform to the degree.Results show that the Chinese specification（DL/T5057-2009&GB50010-2010）,American standard specification（ACI318-2014）and Russia（CΠ52-101-2003）,ignoring the effect of longitudinal steel reinforcement ratio,causing the results be safe,and the discrete degree is higher;The European specification（EN1992-1:2004）is well considered and the calculated results are in good agreement with the experimental results.The formula in this paper can achieve a prediction accuracy comparable to that of the European code（EN1992-1:2004）,and can reasonably reflect the impact of concrete strength and longitudinal reinforcement ratio on the shear bearing capacity,which can provide reference for the revision of the corresponding code. |
