Mechanical Behaviors Of I-Steel-Concrete Composite Beam Under Torsion

With the widespread application of steel and concrete composite beams in buildings,bridges and other engineering fields,researches related to composite beams are gradually become a focus.However,there are less design criteria of torsional I-steel-concrete composite beams in the existing specifications.And domestic and foreign scholars only consider the torsional contribution of concrete slab in the process of researching torsional composite beams.The negligence of composite effects and the torsional contribution of steel beams is detrimental to giving full play the torsional potential of composite beams.Therefore,this thesis conducted in-depth research on the torsional behavior of composite beams based on finite element method in order to reveal the working mechanism and propose related calculation,and the main works are as follows:(1)Based on the plastic-damage and elastic-plastic hardening constitutive models,A kind of 3D finite element model of the steel and concrete composite beams under pure torsion and bending-torsion were put forward and verified by test results,the model could simulated the change rule of load-displacement curve and mechanical properties of each component effectively,the calculation results have good agreements with the test results in torsion bearing capacity,the force and deformation meet the requirements of analysis;(2)Full scale finite element models of composite beams under pure torsion were established to conducted analysis.The influence of material strength,geometric parameters and reinforcement ratio were discussed,then the stress mechanism of concrete slab,steel beam and studs in composite beams,were revealed,respectively.The torsional strength of concrete slabs increases by 10% benefit,and the proportion of steel beams bearing torsional strength is about 16%.(3)Full scale finite element models of composite beams subjected bending-torsion were established to analyze the mechanical properties.The limit of the bending-torsion ratio μ=6 of failure mode was defined and the influence of the loading sequence of bending moment-torque on the bearing capacity of was studied.Then the stress variation law of concrete slab and steel beam in bending-torsion composite beam was revealed through comparative analysis.Finally,the effects of different material strength,stirrup reinforcement ratio,geometric dimension and shear connection degree on the correlation curves of flexure and torsion were discussed.(4)Based on the superposition principle,the practical formulas to predict torsional stiffness and bearing capacity were proposed.With the comparison of results obtained by experiments,the finite element and various formulas,respectively,the calculation accuracy of the formula proposed in this paper was verified.