Influences Of Shear Lag Effect In Steel-concrete Composite Members Under Flange In Tension

Shear lag effect is a significant phenomenon to be considered in design of members with flange.For steel-concrete composite beams and non-rectangular steel reinforced concrete(SRC)structural walls,the shear lag effect can be more significant due to the cracking of the concrete slab reduces its shear stiffness.Despite this phenomenon directly influences the mechanical behavior and the prediction of the bearing capacity and stiffness in design of those members,there is still limited knowledge about the influences of main design parameters on shear lag effect of those members when the flange is in tension.In addition,a method for calculating the shear lag effect in those flanged members under flange in tension is still not available.In this paper,numerical analysis models of steel-concrete composite beams and flanged SRC structural walls were established.Several groups of existing experimental data calibrated those models.Calculation methods of shear lag effect ratio were proposed to evaluate the influence of shear lag effect in flanged members under flange in tension.Based on the calibrated numerical model,the influences of the width of the flange,longitudinal reinforcement ratio,transverse reinforcement ratio,slab thickness,and concrete grade on the shear lag effect of steel-concrete composite beams were investigated.Continuous steel-concrete composite beams under three load conditions,including two equal concentrated loads acting at asymmetric positions,two unequal concentrated loads acting on two spans respectively,and evenly distributed load were investigated.The distribution and evolution of the shear lag effect ratios along the span direction under various load levels in those beams were analyzed and compared.The Shear force distribution of shear studs in those beams were provided by numerical results.On the other hand,the test result of the shear behavior and shear lag effect of T-shaped SRC structural wall TW1 were presented.Based on the calibrated numerical model,the influence of flange width,wall height,axial load ratio,concrete grade,transverse reinforcement ratio,steel reinforcing ratio in the flange,and ratio of total longitudinal reinforcing in the end to the middle of the flange on shear lag effect of T-shaped SRC shear wall were investigated,while the influences of shear span ratio,axial load ratio,transverse reinforcement ratio,steel ratio and concrete grade on the shear stiffness and the portion of shear deformation were further discussed.In addition,based on the constant angle truss analogy model and the variable angle truss analogy model,methods for calculating the shear lag effect of steelconcrete composite beam sustaining hogging moment and flanged SRC structural wall under flange in tension were proposed,respectively.Meanwhile,the truss analogy model was also used for predicting the shear stiffness of the SRC structural wall under various load levels.Finally,the proposed methods were validated against available experimental data and numerical results.The main conclusions are as follows:(1)When the shear wall TW1 yielded with flange in tension,the shear deformation accounted for 53% of the total lateral deformation,and the longitudinal strains in the reinforcing bar and profile steel at the flange end were approximately 54% and 72% of that in the web end,respectively.(2)The shear lag effect of steel-concrete composite beams subjected to hogging moment increases with the increase of flange width and longitudinal reinforcement ratio and decreases with the increase of flange thickness,transverse reinforcement ratio,and concrete strength.Besides,before the yield of composite beams,the shear lag effect becomes more serious with the increase of the load level.(3)For the continuous steel-concrete composite beam,the shear lag effect ratio increases with the increase of the distance from the intermediate support,and negative shear lag effect can be observed in the section far away from the intermediate support.In addition,both the load combinations and the load level have a significant influence on the degree and distribution of shear lag effect in the beams.The influence of the load on the shear forces of shear connectors in composite beams is the main reason for the variation of shear lag effect ratio in each section.(4)The shear lag effect of the SRC structural wall with flange was found to increase with the rising of transverse reinforcement ratio,flange width,and the ratio of the steel in the middle to the end of flange and reduce with the increase of wall height and axial load ratio.Among them,the influences of wall height,flange width and the ratio of end to middle steel ratio on shear lag effect are most significant,while the influence of the axial load ratio is the least.Besides,the influences of the steel ratio in the flange and concrete grade on the shear lag effect are rather limited.(5)The influence of shear span ratio,axial load ratio and concrete grade on the ratio of yield shear stiffness to elastic shear stiffness of T-shaped SRC structural wall can be ignored.Rising the transverse reinforcement ratio and longitudinal steel ratio can increase the ratio of yield shear stiffness to elastic shear stiffness.(6)With the increase of shear span ratio,the proportion of shear deformation decreases significantly.Except for the SRC structural wall with a shear span ratio of 2.5,the proportions of shear deformation at the yield load stage and the peak load stage are basically the same.In addition,the proportion of shear deformation increases significantly with the increase of the steel reinforcing ratio and decreases with the increase of shear span ratio and transverse reinforcement ratio.Increasing the transverse reinforcement ratio can slightly reduce the proportion of shear deformation of SRC structural walls after the yield load stage.The concrete grade only affects the proportion of shear deformation before the cracking stage,while the axial load ratio has a limited effect on it.(7)Compared with the existing experimental data and numerical analysis results,the proposed methods can capture the above-mentioned influence rules well,and the shear lag ratio or shear stiffness predicted by the proposed methods are generally conservative.