Study On The Mechanical Properties Of The Multi-span Continuous Steel-concrete Composite Box Girder

In this paper,the multi-span continuous steel-concrete composite box girder is studied and analyzed.The main contents are as follows:(1)The deformation law and failure mode of multi-span continuous steel-concrete composite box girder under external loads are analyzed based on the test.That is to say,the following things are analyzed,including the load-deflection relationship,the distribution law of slip length along the beam,the load-in-body strain relationship,strain distribution along the floor of the beam and strain distribution along the height of the beam.(2)By calculating the simplified model,the expression of the cracking length in the negative bending moment region of the concrete is established,and the cracking load is calculated.The section properties are calculated by using the conversion section method.The variable stiffness method is used to consider the effect of concrete cracking in the negative moment region of the concrete on stiffness.That is to say,only taking the contribution of the steel girder and the steel bar to the stiffness in the cracking zone into consideration;at the same time,introducing the slip coefficient and considering the slip effect on reducing the stiffness.The principle of virtual work is applied to establish the expression of the deflection caused by the external load and the expression of the inverse arch deflection produced by the prestress increment.Then the total deflection is calculated by their superposition.At the same time,a contrastive analysis of the deflection considering the cracking phenomenon and that without considering the cracking phenomenon is carried out.A contrastive analysis of the deflection considering the slip effect and that without considering the slip effect is also done.The results show that the cracking of the concrete and the relative sliding of the interface have a greater influence on deflection.Considering the influence of prestress on the deflection of the composite beam,the application of prestress can increase the cracking load of the steel-concrete composite beam and delay the cracking of the concrete in the negative bending area of the composite beam.But its influence on the mid-span deflection is not significant.(3)The failure load of the composite beam is calculated and the shear stiffness coefficient of the composite beam stud is obtained by fitting the shear-slip data of the stud.The relational expression between shear force and slip of composite beams is established and is contrastively analyzed with experimental values.