Research On Effective Flange Width Of Assembled Steel-Concrete Composite Flat Beam

Steel-concrete composite beams have been widely used in engineering,because of their excellent fire resistance,seismic performance,high stiffness,strong bearing capacity and low cost,the research on the mechanical properties of composite beams has been a hot spot in civil engineering.Aiming at the application of steel-concrete composite beams in assembled high-rise buildings and long-span bridges,this paper presents a new type of assembled steel-concrete composite flat beam structure,designs and finishs seven bending tests of composite flat beam members,and designs three width-span ratios,three load types,three channel steel types and three material strength ratios on the basis of comparison and fitting with experimental data,a total of 81 finite element simulation members were studied.The distribution of longitudinal stress and the variation of effective width of flange under different parameters were studied.Finally,theoretical formulas for calculating effective width of flange of composite flat beam under three modes of two-point loading,concentrated loading and uniform loading were put forward,which provided basic information for deepening the research theory and engineering design of composite flat beam.The experimental results show that the longitudinal stress in the middle span of composite flat beams is nearly uniform distribution,and the effective width is basically constant;the larger the width-span ratio,the smaller the effective width coefficient is;while the factors such as the type of channel steel,the height of steel beams and the reinforcement ratio have little effect on the effective width.With the increase of load,the concrete reaches the ultimate value of compressive strength,and the composite flat beam enters the stage of plastic loading,then the effective width decreases gradually with the increase of load.The finite element software ABAQUS is used to build the three-dimensional model of the test beam components,the factors of material nonlinearity and geometric nonlinearity are taken into account in the process of modeling and analysis.Based on the comparison of experimental data,a finite element model with good fitting effect is established,and the effects of width-span ratio,load type,channel steel type,material strength ratio and shear spacing on the effective width of flange plate of composite flat beam are discussed by using this method.It is found that the main parameters affecting the effective width of flange plate of composite flat beam are width-span ratio and load type.The bigger theeffective width is,the smaller the effective width is;under two-point loading and uniform loading,the difference of the effective width of the flat beam is not big,but under concentrated loading,the effective width is smaller than the former two loading conditions;The higher the type of channel steel,the greater the material strength ratio,the higher the height of steel beam and the smaller the spacing between shear components,so the greater the flexural rigidity and the flexural bearing capacity of flat beam,but these factors have little effect on the effective width of flange.On the basis of model test and simulation analysis,theoretical formulas for calculating effective width under two-point load,concentrated load and uniform load are proposed,compared with the effective width standard value,the theoretical value is smaller than the theoretical value based on bolt shear.Combined with the deduced calculation method of flexural capacity of composite flat beams,the calculated results are compared with the experimental values,and they are in good agreement,which shows that the proposed design method is reliable.The experimental and theoretical analysis results of steel-concrete composite flat beams can be used for reference in engineering design and related research.