Study Onthe Crack Width Of Double COmposite Continuous Beam Considering Concrete Damage

The top concrete slab of double steel and concrete composite continuous beamwill crack under tension in the negative bending region. This dissertation analysesproblems in the development and influence factors of crack, which is based on thesystematical analyses of experimental phenomenon and data of the test specimenthrough numerical calculation by using the FE software ANSYS.It is modeled as a plane problem for the tested 2-span double steel and compositecontinuous beam specimen with full shear connection. The effect of the interfacebond and slip between concrete and steel is expressed by nonlinear springs of nulldimension at the nodes, and the concrete under tension is assumed as a tensile strainsoftening material. The whole process from loading to collapse is simulated for thespecimen by using the powerful ANSYS Parametric Design Language (APDL), inwhich the tension crack width is computed by the relative displacement change of theneighbor joints. There is a good agreement by comparing of the crack location andwidth between the test measurement and the numerical simulation. It is possible touse FEM to evaluate the crack width for double composite beams.On the base of the specimen model, this dissertation discusses the effect of thethickness of the bottom concrete slab to the double composite beam crack. By usingmethod of least squares, the curve fitting is done to the load and deflection curve aswell as the load and the maximum crack width curve with different thicknesses, andthen the corresponding calculation formulas are got. It shows the thickness of thebottom concrete slab is effective to decrease the crack width and increase thestructure stiffness.In addition, this dissertation discusses the effect of concrete ultimate tensilestrain. Using the same method, the curve fitting is done to the load and deflectioncurve as well as the load and the maximum crack width curve with different ultimatetensile strain, and then the corresponding calculation formulas are got. The resultsindicate that concrete crack is a progressive process. When considering tensile strain softening, crack is put off and its width decreases by improving the ultimate tensilestrain. In particular, crack resistance improves significantly by usinghigh-performance concrete.