Effect Of Reinforced Concrete Slab On The Flexural Behavior Of Composite Beam To Column Joints

In recent decades,earthquake disasters have occurred frequently,causing the damage and collapse of a large number of buildings.Many studies have found that the failure of steel structures or composite structures mainly occurred at the beam-column connection,the combined effect of reinforced concrete(RC)slab and steel beam is often ignored.The composite action between RC slab and steel beam was regarded as a safety stock,and the design method had the possibility of turning "strong column and weak beam" into "strong beam and weak column".Therefore,it is necessary to consider the combined effect between RC slab and steel beam when studying the seismic performance of composite connection.This paper mainly conducts a comprehensive numerical and theoretical analysis on the flexural bearing capacity of RC slab composite connection.The experimental specimens include 2 beam-column joints without slab and 2beam-column composite joints with reinforced concrete slab.On that basis,the paper uses finite element analysis software ABAQUS to establish finite element model.Under the premise of verifying the accuracy of the results obtained by the FEM,the mechanical performance and failure modes of the joints under the influence of size effects,the height-to-width ratio of the panel zone,the thickness of the RC slab,the concrete compressive strength and the column width-to-thickness ratio are studied.Based on the theory of yield line mechanism,a calculation method for the flexural capacity of composite connection is proposed.The conclusions are showing as follows:(1)Compared with the results obtained from the finite element model and those obtained from the test,it was found that the fitting degree is higher.And compared with failure modes between the finite element model and the failure modes obtained from test,it is found that the failure modes obtained from the finite element analysis are basically consistent with those observed in the test,which proves that the accuracy of the model meets the requirements and can be used for further parameter analysis.(2)Parametric analysis was carried out for the performance of beam-column connection considering the action of RC slab.The effect of size effects,the height-towidth ratio of the panel zone,the thickness of the RC slab,the concrete compressive strength and the column width-to-thickness ratio are studied.It is found that the ratio of the flexural capacity of the beam end per unit section is 0.84～1.38,which indicates that the size effect is one of the main parameters affecting the flexural capacity of the composite beam.(3)With the increase of the height-to-width ratio of the panel zone and the thickness of the RC slab,the depth of the composite beam increases.Hence,the yield moment and plastic moment of the composite beam are increased under positive loading and negative loading.Due to the combined effect of between the RC slab and the steel beam,the performance of composite beam under positive hogging is greatly improved;With the increase of the concrete compressive strength,the yield moment and the plastic moment respectively increase under the positive hogging,which proves that the concrete strength has a significant effect on the bending moment of the composite beam.;With the increase of the column width-thickness ratio,the beam end rotation angle in the joint panel zone increases gradually,and the beam end displacement angle decreases relatively,leading to the failure of the specimen in advance.The bending moment of the composite connection also decreases with the increase of the column width-thickness ratio.It is proved that the height-to-width ratio of the panel zone,the thickness of the RC slab,the concrete compressive strength and the column width-to-thickness ratio are the key parameters that affect the seismic performance of the composite connection.(4)The failure of the specimen considering the effect of the RC slab mainly occurs at the lower flange of the beam.Tensile and compressive strains are formed at the outer annular stiffener,and extended to the beam end with a 45-degree angle as the boundary.The main damage area of the panel zone concrete is close to the lower flange of the beam.The RC slab failure begins near the square steel tube column and expands along45 degrees.(5)Based on the theory of yield line mechanism,a calculation method for bending capacity of composite beams is proposed.The calculated results are in good agreement with the finite element analysis results.The flexural bearing capacity of composite connection calculated by the formula is 87%～106% of finite element analysis results,which proves that the proposed calculation formula has a good accuracy and can be used in the design of composite joints in steel or steel-concrete structural systems.