Research On Punching Shear Behavior Of Reinforced Concrete Isolated Column Footing Under Eccentric Compressive Load

It is generally known that reinforced concrete(RC)isolated column footing is convenient for construction,low in cost and widely used in engineering.It has become one of the most common footing form,and its application range is very wide.The punching shear failure of RC isolated column footing is brittle,which may cause the progressive collapse of the whole structure.Therefore,it is of practical significance to study the optimization design of RC isolated column footing,and it is necessary to discuss the punching shear mechanism of eccentric compressive isolated footing.In this paper,the punching shear failure tests of three eccentric compressive isolated column footing with different flexural reinforcement ratio(0.82%,1.01%,1.19%)have been carried out.The experimental data such as load central deflection curve,concrete and reinforcement strain,crack distribution in foundation’s side and back surface,ultimate failure load and soil pressure distribution are obtained.The test shows that the smaller the flexural reinforcement ratio of column footing,the smaller the punching shear capacity,the greater the central deflection of footing when footing failures,the more fully the development of the punching shear failure surface,and the more ductility of RC isolated column footing.According to the test results,the flexural reinforcement ratio is increased by about 45%,and the punching shear capacity is only increased by nearly 10%.The nonlinear finite element software ABAQUS is used to establish the spring model and the Mohr-coulomb foundation model to simulate the punching shear failure process of RC eccentric compression isolated column footing,and the feasibility o f using the spring foundation model to simulate the punching shear failure of the isolated footing under the real soil consolidation is verified,and the influence of 6 parameters,such as the flexural reinforcement ratio,eccentricity,concrete strength,effective height,loading surface shape and coefficient of foundation bed,on the punching shear failure of isolated footing are studied.Based on the experimental results in this paper and the experimental results collected in the database,the formulas of the Chinese concrete code(GB50007-2011),American code(ACI318-14)and European code(Eurocode2-2004),and various column footing punching capacity calculation formulas are compared,and the reasonableness of each parameter is measured.Then,based on the assumption of shear stress distribution by American code ACI,the regression formula for punching shear capacity is put forward,which is in good agreement with the experimental data.The failure load on the top of the column can be calculated directly.It is suitable to predict the bearing capacity of the isolated column footing in the project.If the formula is used in the design,the partial coefficient of the concrete material can be considered or the reduction coefficient is multiplied by the formula to obtain a certain guarantee rate.