Theoretical And Experimental Research On Mechanical Properties Of Composite Truss

Steel- concrete composite truss girder is made of reinforced concrete slab, shear connectors, steel truss synergistic combination of the force of flexural members,under the same conditions, this combination compared to traditional composite beam member has greater stiffness and load capacity, with high economic value and use.But the steel- concrete composite truss girder is also less in the country, in its infancy,a large space to match the theoretical and experimental research project uses exist,especially for the lack of domestic engineering design and calculation of required design basis formula.The effective width of composite, the effect of interface slip and uplift of composite, the deflection of composite truss, and the ultimate flexural capacity and ultimate shear capacity of composite have been studied systematically, based on the test of three composite beams combined with the numerical simulation and theoretical derivation.The main research contents of this paper includes:1.Based on the finite element method, a plurality of groups of single trusses and three trusses beam finite element model, and the parameter analysis was carried out.Analysis results show that the effect of load type, concrete slab thickness and shear connection degree to the width of composite beam is very small, and it shows that the witdth of composite beam was greatly affected by wide span ratio and high span ratio.Considering the parameter of wide span ratio and high span ratio, the calculation formula of effective width was given by the data fitting method, which made up the blank of the existing specification, and it has a strong engineering value.2. Considering five cases of load situation and the effect of of interface slip and uplift, the differential equations of unit lift force and axial force were established by formula theory deduction method, and the exact solution and approximate solution were given.According to summary and conclusion, and the regularity of lift force was put forward. Numerical results show that the lift force nearing support can not be ignored, which should be considered in design.3.Three composite beam with different shear connection degree have been tested.Through experimental study, the stiffness, deflections, bearing capacity and failure mode of composite beams have been studied systematically, and the comparative analysis with theoretical calculation results was carried out.4. Considering five cases of load situation and the effect of interface slip and uplift, the internal mechanisms of the influence of interface slip and uplift on deflection of composite beams was investigated, and the deflection of composite beam was proposed by formula theory deduction method. The formula can be applied to the composite truss and gereral composite beam. The test results and numerical analysis results both show that the formula for calculate deflection of composite truss was accurate and reasonable.5. Tensile strain calculation formula for entire interactive composite truss and partial interactive composite truss was proposed by formula theory deduction method.According to the shear connection degree, the composite truss is divided into two types: fully connected composite truss and partial connected composite truss, and the ultimate flexural capacity formula of the both type were proposed. On the basis of existing specification, the calculate method of the ultimate flexural capacity and ultimate shear capacity of composite were given.