Analysis Of Shrinkage And Creep Effects Of Steel-Concrete Composite Beams

The steel-concrete composite beam is a member composed of a rigid shear joint connecting the concrete slab and the steel beam.Due to the long-term load of the concrete slab in the composite beam,shrinkage and creep will occu r and the internal force will be redistributed.Even if the external force does not change,the internal force of the structure changes with time,which may affect the safety a nd use of the structure.Therefore,this paper studies the shrinkage and creep mec hanical properties of steel-concrete composite beams by theoretical derivation.The internal force redistribution and deflection deformation calculation method of the composite beam shrinkage and creep are analyzed and deduced.The analytic expressions of the internal force redistribution are derived by using the differential constitutive and algebraic constitutive,and the solution is verified by an example.The main work and conclusions of the paper are as follows:(1)Based on the principle of linear superposition,the integral constitutive,Dischinger differential constitutive and Trost algebra constitutive equations of concrete shrinkage and creep are derived.Using the differential constitutive,the free shrinkage and creep of concrete,the elastic confinement contraction and creep,and the redistribution stress calculation of rigid constrained shrinkage and creep are deduced.For the stress relaxation problem under rigid c onstraints,the numerical method of stepwise integration is used to calculate the relaxation coefficient.(2)Using the Trost algebra constitutive equation,based on the c reep coefficient model of China’s “Design Specification for Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts ”,calculating the concrete relaxation coefficient map,and use this graph to solve the creeping secondary force during continuous beam structure transformation.(3)Using the Dischinger differential constitutive and Tr ost algebra constitutive to solve the pure creep effect and pure shrinkage effect of the symmetrical section composite beam under the pure axial compression and pure bending moment.It is found that under the action of pure bending moment,the degree of re distribution of the internal force of the section is obviously larger than that of the pure axial pressure,and the creep development rate is different.(4)Based on the Dischinger differential constitutive and the Tr ost algebra constitutive derivation eccentricity constraint,the internal force analytical formula of the steel-concrete composite beam shrinkage and creep distribution is obtained,and the exact solution is obtained.Since the concrete slab and the steel beam shape do not coincide in the composite beam,the exact solution requires complex decoupling calculations when solving practical problems.By ignoring the influence of the redistribution bending moment of the concrete slab on the axial strain,an approximate solution under certain applicable cond itions is obtained.The example shows that the result of the app roximate solution has less error with the result of the exact solution and can be used to solve the shrinkage and creep in the engineering.