Experimental Study On Bending Performance Of RC Beams Considering Axial Restraint Effect Under Earthquake Action

RC frame beam after peripheral component constraints the flexural crack and yield of axial elongation,lead to beam axial force and significantly influence the flexural performance,studies of the effect of structural seismic response is very limited,but it is likely to lead to "strong beam weak column" and even collapsed structures.The axial constraint effect on the flexural bearing capacity of the beam,the bending stiffness,the influence of plastic deformation ability is unclear,the related "strong column weak beam" in the study of nonlinear analysis of the structure of not considering the influence of beam axial constraint effect,actual flexural bearing capacity of beams can be significantly undervalued,the proposed "increases the bending moment at the end of the coefficient" may still no guarantee that the structure achieve the failure mode under seismic action.Therefore,it is urgent to carry out systematic and in-depth basic research on the flexural performance of RC frame beams with axial constraints,both in terms of knowledge and engineering application.In this paper,a quasi-static test method is used to study the bending properties of RC frame beams with axial constraint effect under seismic action.Analysis of RC frame beam bending cracking and yielding rear axle to elongation mechanism and influence factors,by the equivalent restraint stiffness substructure test,to explore the axial constraint effect on the beam bending strength,bending stiffness,the influence of plastic deformation ability,and reveal the axial restraint effect of different reinforcement ratio flexural performance of RC frame beams are studied.This study will provide a basis for the study of RC frame structure seismic performance and strong column weak beam design method.Through comparative analysis of test results,the following conclusions are obtained:(1)When the displacement Angle of the interlayer is increased to 4%,there are no constraint specimens 1 and 3,and the elongation is 15.2mm(-17.1mm)and 17.9mm(-19.0mm)respectively;The elongation is 6.0mm(-6.3mm)and 5.4mm(-5.5mm)respectively.The yield of unconstrained beams will be elongated after bending.(2)When the displacement Angle of the interlayer is equal to 5%,the axial force of the constrained specimen 2 is 488KN(482KN),and the axial compression ratio is 0.18(0.17).The axial force of the constraint specimen 4 reaches 392KN(392KN).The axial compression ratio reached =0.16(0.16).It is obvious that because of the constraint,the RC frame girder is stretched,which leads to an ununderestimated axial force in the beam.(3)A constraint specimen 2 than unconstrained specimen 1 flexural bearing capacity increased by 58.1%,there are constraints specimen than 4 unconstrained specimen 3 flexural bearing capacity increased by 47.7%,at the same time there are constraints specimen 2 relative to the unconstrained specimen 1 and constrained specimens 4 relative to the specimen 3 ability of energy consumption has increased significantly,bending stiffness,but slightly lower plastic deformation capacity.(4)There are constraints,low reinforcement ratio increase the flexural bearing capacity of the specimen 2 is higher than the constraint high flexural bearing capacity of reinforcement ratio specimen 4,axial constraint effect on the improvement of the performance of the low rate of reinforcement beam bending amplitude is more significant than high beam reinforcement ratio.(5)Based on the experiment,the axial constraint will increase the shear demand of the node area.