Mechanical Properties Of New Plate-truss Composite Structur

With the development of large-span composite structure technology,steel-mixed structure has been widely used.In this paper,a new type of structural form – SSTC is proposed.By studying the mechanical properties of plate-truss composite beams,some formulas for the design of deflection,bearing capacity and shear lag effect are summarized.SSTC consists of a plate-truss and an upper concrete slab.The plate truss is composed of pressed steel plate(different from the use of floor),stiffening ribs,lower string bar and middle belly bar,forming an inverted triangle section,which has the advantages of higher bearing capacity,greater stiffness,superior space performance,more saving steel and high space utilization rate.The calculation formula of the ultimate bearing capacity of the structure was derived based on the simplified plastic theory to study the deflection and bearing capacity design method of the new slab truss composite beam,The finite element software was used to study the design parameters of the concrete strength,the thickness of the concrete slab,the width of the concrete slab,the thickness of the molded steel plate,the cross-sectional area of the lower boom and the height of the beam,and the applicability of the bearing capacity formula was verified.The influence of different parameters on ultimate bearing capacity is discussed.The deflection of composite plate-truss beams is equivalent to the flexural deformation deflection of dummy beams and the shear deformation deflection of dummy truss beams.Based on the principle of virtual work,the calculation formula of the deflection is proposed,and the method of finite element is used to compare with the calculation formula of the deflection.The results show that the formulas of ultimate bearing capacity and deflection is consistent with the measured finite element values,and the accuracy and applicability of the formulas are verified.Concrete slab width,concrete strength,beam height,cross-sectional area of lower chord and thickness of concrete slab have great influence on the bearing capacity.The ultimate bearing capacity of plate-truss composite beams increases by 28%,32.7%,35%,41.4% and47.6%,respectively,when each parameter is doubled.The influence of steel plate thickness on ultimate bearing capacity is almost negligible.The cross section stress of the plate truss composite beam is analyzed,and the influence of the width to span ratio,overhang ratio and width to height ratio on the shear hysteresis effect of the plate truss composite beam is considered.Based on the energy method and the minimum potential energy principle,the calculation formula of the transverse section stress and the calculation formula of the deflection considering the shear hysteresis effect of the concrete slab are derived,and the correctness of the stress calculation formula in the transverse section is verified.At the same time,the practical design formula is fitted by combining the formula and the finite element solution in the section with the error.The results show that the calculation formula of normal stress in cross section and the modified design formula are proved to be reasonable.The error between the deflection formula and the finite element considering the shear hysteresis effect is 0～2.5% in the elastic stage,which indicates the correctness and applicability of the deflection formula and the finite element model.The effect of width to span ratio and overhang ratio on shear hysteresis of plate truss composite beam is great,while the effect of width to height ratio on shear hysteresis is small.