Experiment and calculation on torsion bearing capacity of concrete composite box section with corrugated steel webs and steel truss webs

To investigate the torsion behavior of concrete composite box sections with corrugated steel webs and steel truss webs, the torsion bearing capacity experiments were carried out. It is found that the diagonal cracks, perpendicular to the principal tensile strains of concrete, first appeared at the bottom plate. Then the cracks spirally developed at both the top and the bottom plates, and the angle between the cracks and the longitudinal axis of the main girder was approximately 45 degrees. Eventually, some larger diagonal cracks were observed at the bottom plate, and the specimens failed by torsion damage after steel rebar yielded in tension. The nonlinear finite element analysis (FEA) for torsion test specimens was simulated using finite element software ANSYS, and the results obtained by FEA agreed well with test results. The cracking torque formula of composite box sections was proposed with reference to the formula of concrete box girders. Using the variable-angle spatial truss model for concrete box girders, the formula of the ultimate torque for composite box sections was established according to the three probable torsion failure modes. In comparison with the results of model test and finite element analysis for actual structural size, the proposed formulas of torsion bearing capacity of concrete composite box sections with corrugated steel webs and steel truss webs had high accuracy, and the maximum error was less than 10%. The proposed formulas can be applied in practical bridge calculation.