Analytic Research On Concrete Box Column Seismic Performance Based On The Shear Lag Effect

Reinforced concrete box column is specified for its characteristic of closed section,which shows good performance of stress,so it is widely used on bridges.However,under low level cyclic loading,the influence of shear lag effect on the seismic performance of concrete box column cannot be ignored.Without considering the influence of shear lag effect will lead to underestimate the stress at the junction of the flange and web member,which will cause instability and failure of the component.Therefore,in order to study the shear lag effect on the seismic performance of concrete box column,on the basis of the existing theory,combining with the piers condition of Shanxi province Huluhe bridge,3concrete box column are designed in the paper.Taking 3 reinforced concrete box column as simulation object,this paper has analyzed the influence of wall thickness ratio and height to width aspect ratio on the shear lag effect,based on the analysis of the above parameters,the shear lag effect of concrete seismic performance can be clearly concluded,analysis results show:(1)The influence of the variation of the longitudinal wall thickness ratio on the shear lag effect of the concrete box column is obvious,which shows the shear lag is the positive shear lag in the edge of the solid end flange,and the middle of the wing plate is negative shear lag.(2)With the shear lag coefficient of height to width aspect ratio increasing at the edge of the wing plate,and the shear lag of wing plate in the middle(negative shear lag)number decreases.(3)The shear lag effect of column box have certain effects on the shape of hysteresis curve,and when the shear lag is smaller,the hysteresis curve becoming full,seismic performance getting better;with the increase of shear lag,the maximum load is also changing,which leading to the larger shear lag and smaller maximum load.(4)The secant stiffness of concrete column box decreases with the increase of the shear lag effect.The ductility coefficient of three concrete box column are between 2.5~3.5,which shows pronounced ductility.The displacement ductility coefficient of the specimen with bigger shear lag effect was significantly lower than that with smaller shear lag effect,and the deformation ability is small.(5)Using the energy variational methods,the calculation formula of concrete box column deflection is derived,and the conversion section method can be used for the analysis of cracking of concrete box column before.After considering the influence of shear lag effect,the displacement of concrete box calculate value will increase on the elementary beam theory,and the increase range is from 6% to 10%.So the shear lag effect in practical engineering can not be ignored.In this paper,based on the finite element analysis and theoretical analysis,which concluded that the effect of shear lag has effects on the seismic performance of concrete box,and it has a certain reference value to enrich the theory and the follow-up study as well.