Study On Flexural Behavior Of Spliced Steel-Concrete Shallow Composite Beam

Shallow composite beams have been widely used in steel-concrete composite houses because of their ability to effectively reduce the building height and improve the fire resistance.However,the section height of traditional shallow composite beam is usually small and its flexural capacity and flexural stiffness are relatively low,which undoubtedly weakens the application of shallow composite beam in practical engineering to a certain extent.Therefore,in this thesis,a spliced steel-concrete shallow composite beam structural form is proposed to improve the low flexural capacity and flexural stiffness of traditional shallow composite beam by designing a new cross-section.In this thesis,three spliced steel-concrete shallow composite beams were designed and tested in four-point bending to investigate the bending performance of spliced steelconcrete shallow composite beams with different forms of shear resistance(specimen SBBs with shear resistance only by the steel-concrete bond and specimen SB-Wb with shear resistance only by the slotted shear connection)and different spacing of slotted shear connections(specimen SB-Wb with 150 mm spacing and specimen SB-Wb2 with 300 mm spacing).SB-Wb and SB-Wb2 with 300 mm spacing).At the same time,based on the equivalent force method and the equivalent rectangular stress block method,the calculation formulae for the flexural load capacity and flexural stiffness of the spliced steel-concrete shallow composite beam were derived.The accuracy of the formulae is verified by comparing the simulation results with the formulae.In addition,the effects of different parameters on the flexural performance of the spliced steel-concrete shallow composite beam were investigated.The main conclusions are as follows.(1)Specimen SB-Bs,specimen SB-Wb,and specimen SB-Wb2 all had ductile damage and roughly the same crack distribution,mainly located in the area on both sides of the loading point;in addition,the transverse and longitudinal strain distributions along the cross-sectional direction were similar for the steel and concrete in the three specimens during the stressing process,which indicated that the combination of the two materials worked well;in the ultimate condition,there is no obvious relative slip between the steel and concrete in the three specimens(the end slip is 1.1mm,0.36 mm and 0.63 mm,respectively),which indicates that the three specimens have achieved a complete shear connection.(2)By comparing the flexural performance of spliced steel-concrete shallow composite beam(specimen SB-Bs and SB-Wb)with different forms of shear resistance,it was found that the flexural performance and ductility of specimen SB-Bs with shear resistance by the steel-concrete bond alone was better than that of specimen SB-Wb with shear resistance by the slotted shear connectors only.By comparing the flexural performance of the spliced steel-concrete composite flat beam(specimen SB-Wb and specimen SB-Wb2)with different spacing of slotted shear connectors,it was found that the ductility increased to some extent with the increase of the spacing of slotted shear connectors and the peak load decreased,but the decrease was less than 1%.(3)Based on the equivalent stress method and the equivalent rectangular stress block method,the limit equilibrium method is used to derive the formula for the flexural load capacity of the spliced steel-concrete shallow composite beam with different shear connections(partial shear connection and fully established connection)and the error is found to be less than 3% by comparing with the test results,which shows that the proposed formula is more accurate.In addition,the formula for the flexural stiffness of the spliced steel-concrete shallow composite beam in the elastic phase is derived by using the commutative section method.(4)By establishing five finite element models with different shear connection coefficients,the formula of flexural capacity of partially shear connected spliced steelconcrete shallow composite beam was verified;the results showed that the maximum error of the formula results,simulation results of the five models was about 6%.By comparing the flexural performance of the finite element models with different shear connection coefficients,it is found that with the decrease of the shear connection coefficient(1～0.6),the flexural load capacity of the spliced steel-concrete composite flat beam gradually decreases,with the maximum decrease of 8%,but the redistribution capacity of the shear stress at the interface between the steel section and concrete in the spliced steel-concrete shallow composite beam gradually increases.(5)By establishing nine finite element models with different cross-sectional dimensions,the equations of flexural load capacity and flexural stiffness of the fully shear connected spliced steel-concrete shallow composite beam were further verified;the results showed that the errors of the results and simulations of the flexural capacity and flexural stiffness of the nine models were less than 5%.By comparing the flexural performance of the finite element models under the influence of different parameters,it was found that increasing the concrete strength and increasing the concrete slab size(width and thickness)could simultaneously improve the flexural capacity and flexural stiffness of the composite flat beam,with the increase ranging from 2.2% to 22.9%.