Study On Key Joint And Shear Lag Effect Of Steel-Concrete Composite Truss Bridge

The steel-concrete composite truss bridge is widely used in practice because it is economical, better capable of spanning and convenient to maintenance. The joint is the key member of this kind of bridge, which must possess the reasonable strength, rigidity and failure mode to ensure the integrity of the bridge. At present, it is in lack of enough understanding of the bearing performance and failure mode of the bridge in consideration of the complex boundary condition, that is, allowance for bending moment from bridge deck and web member, and vertical deflection of both side of bridge deck. What’s more, the shear lag effect caused by the non-continuous distribution of joints is lack of sufficient understanding. This dissertation is to study the bearing performance and failure mode of the steelconcrete composite truss bridge, as well as the shear lag effect through the finite element simulation and experimental research. This dissertation mainly includes the following three parts:Nonlinear finite element analysis of the joint of the steel-concrete composite truss bridge. An ABAQUS model under complex boundary conditions was built and was performed a nonlinear simulation. It is done that the analysis of loaddisplacement curve, the plasticity distrib ution and failure mode which shows that the load-displacement curve has no obvious yield point. The plasticity distribution of members is different from it in ordinary shear test. The failure of concrete in perfobonds causes the failure of the whole joints, but there may be different failure modes.Experimental study and parametric analysis of the joint of steel-concrete composite truss bridge. In order to analyze the load-displacement curve, skeleton curve, the stress conditions and the failure modes of the specimen, it is carried out that repetitive loading test of the joint specimen under complex boun dary conditions. It is performed that the parametric analysis of the joint under the complex boundary conditions after the validation of ABAQUS simulation confirmed by the experimental data. The results of experiment and simulation show that in repetitive loading test, hardening effect and unloading stiffness degradation effect are obvious. Web member are eccentrically loaded. The cracks of the specimen are concentrated outside the surrounding concrete. The strength of the surrounding concrete, the diameter of the perforated steel bar and whether the steel bar exists, have a bit effect on the yield strength, but more effect on the ductility and ultimate strength.Research on shear lag effect of simply supported steel-concrete composite truss bridge. Observation of the normal stress, coefficient of shear lag and effective width in lengthwise and broadwise direction is carried out after simulation of the simply supported bridge under the self-weight is performed by ABAQUS. It is shown that both shear lag and negative shear lag effect exist, which are most serious on the joint, but almost disappear on the midpoint of segment. The maximum effective width of the bridge is almost equivalent to the one calculated by specification of simply supported box girder, but a big gap from minimum effective width.