Research On Bond-slip, Shrinkage And Creep Properties Of Steel Box-concrete Composite Beam

Steel box-concrete composite beams is a new type of composite structure. Theconcrete part mainly arranges at the upper part of the compression zone that gives fullplay to the tensile properties of steel and the compressive properties of concrete.Sincethis kind of composite beam was proposed, the characteristics have beensystematically analyzed and demonstrated,including bending、shear、torsion、localbuckling theory in succession and obtained a series of achievements and pointed outthe concrete and steel plate may have slip effect frequently. Steel box-concretecomposite structure’s upper concrete is enclosed by the steel box, so the concrete partare squeezed from three directions. Whether the concrete and steel plate interfaceslipps,both with the influence degree on the bearing capacity are not conclusive. Athigher stress levels with the increase of the load, the effect on the deflection of thestructure and the influence degree on stress redistribution of the bond slip need furtherresearches. Besides that, the effects of shrinkage and creep of concrete has receivedextensive attention in engineering fields, in consequence of the upper concrete onsteel-concrete composite structure in a closed state, the impact of creep and shrinkageof core concrete on load bearing capacity of structure did not carry out relatedresearch on this kind of component.In this paper, by introducing the calculation theory of bond slip strength of thesquare steel tubular structure filled with concrete condition. According to the forceequilibrium of element and compatibility deformation, established the differentialequations of the bond slip between steel box and concrete which have considering theinfluences of bond slip strength then obtained the analytical solutions of deflectionand theoretical calculation of stress which have consider the slip effect, which agreedwith experimental data.For the analysis of long-term effects under loades, through the use of equivalentelastic modulus method, both with the introduction of square steel tube concreteshrinkage creep model, together with force equilibrium of element and compatibilitydeformation and consider the effect of differential shrinkage and creep further pushedto the effects of long-term load deflection and stress calculation formula. The resultsshow that the long-term effects incremental percentage is about20%than short-termeffects. The percentage is about7%-8%for steel upper plate and about6%for steelbottom plate. For the study on the effect of slip in order to further verify the theoreticalanalysis, the theoretical analysis and experimental data were added for comparison. Inthis paper, Ansys-finite element analysis software, by introducing combination39unitwith three spring elements, to simulate the bond-slip mechanism of class members.Numerical simulation、theoretical analysis、experimental data have been better unified,which has further validated the feasibility of such methods. Meanwhile, in order tofurther standardize the countries under comparison shrinkage and creep model,similarities and differences between the results of such components, we use midas-feafinite element analysis software to establish an analytical model under seven kinds ofdifferent specifications. The results show that the increment for the additionaldeflection is20%-25%, the increment of additional stress is about8-10%, whichshould cause designers’ enough attentions.