Research On Punching Shear Failure Mechanism Of Eccentrically Compressed Isolated Footing Under The Influence Of Column Width And Eccentricity

In practical engineering applications,the most frequently used form of footing engineering is the isolated foundation.The punching shear failure of the isolated footing is a brittle failure.There is no obvious sign before the damage occurs,which will cause serious consequences,and such damage should be avoided as much as possible.At present,due to the complex interaction between footing and soil,the influence of soil on the mechanism of footing damage is unclear.Most of the existing tests are carried out under compressive load on the axis.However,the footing is usually subjected to eccentric loads.Among them,the influence of column width and eccentricity on punching shear failure under eccentric load is more obvious.Therefore,it is necessary to study the punching shear failure mechanism of eccentrically compressed columns footing under the influence of column width and eccentricity.In this paper,two controlled trials have been carried out.One group considers the influence of column width(200mm,250 mm,300mm),and the eccentricity is set to 100mm;the other considers the influence of eccentricity(0,100 mm,200mm),and the column width is set to 300 mm.The two groups have a total of 5 isolated column footing.The experiment collected the test data of the flexural reinforcement of the foundation slab,the strain of the concrete,the failure load,the reaction force of the foundation slab,the center deflection,etc.,and drew crack patterns of the foundation slab.The load of JC1-30 is 13.6 % lower than that of JC0-30,and the load of JC2-30 is 25.6 % lower than that of JC1-30.The load decreases with the increase of eccentricity,and the reduction rate increases with the increase of eccentricity.The load of JC1-25 is 3.4 % higher than that of JC1-20,and the load of JC1-30 is 19.4 %higher than that of JC1-25.The load increases with the increase of column width,and the growth rate increases with the increase of column width.The punching shear failure tests of five independent foundations in this paper were simulated by ABAQUS nonlinear simulation software.The modified CDP model was used for concrete,the double broken line model was used for reinforcement,and the nonlinear spring was used for elastic foundation.The load-deflection curves of the simulated specimens were compared with the actual test curves,and the reasons for the differences were analyzed.The stress nephogram of steel bar,compressive damage and tensile damage nephogram of concrete are given.When the column width and eccentricity change,the change of stress distribution is analyzed.Forty-nine independent foundation test samples of punching failure,including the specimens in this paper,were collected,and the theoretical value of load,safety factor and variation coefficient of the samples were calculated according to the national codes.The accuracy of GB50007 and Eurocode2 is good,and the theoretical value of ACI318 is too conservative.Eurocode2 of stability are superior to GB50007 and ACI318.The influence of eccentricity and column width on the calculation results is analyzed.