Experimental Research And Numerical Analysis On Stress Mechanism In The Joint Of Two-way Superimposed Slab

In order to meet China’s12th Five-Year Plan and the future development of the housing industry needs, we launch researching on the superimposed slab which contributes a large proportion to fabricated structure. The existing superimposed slab parts only were used as one-way slabs and have weak performance joints, so they can not release the vast bearing capacity, and then cause increasing the cost which brings about slowing down the march of housing Industrialization。Domestic and foreign experts and scholars have done some research on the prefab element and the joint of bidirectional superimposed slab and got some achievements which have some limitations. Research group will carry out research on the carrying force mechanism of superimposed slab in the joint, so as to solve the problem of unidirectional force transferring.Research group study on shear and tensile bond performance of the superimposed slabs, perform analysis of stress state of joints section and lapped reinforcement anchorage stress state and analysis of contribution to superimposed slab’s stiffness and bearing capacity especially in the joint by lattice girder. Using the sub structure theory to establish the stiffness formula; Carring on comparative analysis to the existing bond slip curve, on the basis of this, putting forward a new modified bond slip curve, then using numerical simulation to verify it; According the research results, we put forward some new constructional details and through carrying out tests and numerical simulation on some specimens to validate the theoretical model. Finally, we propose the design rule for applying to bidirectional superimposed slabs.(1) Statistical analysis found that, when the concrete strength is more than C20, laminated surface strength and concrete cube strength shows a strong correlation between shear test and has a significant regression equation; tensile strength of laminated surface tensile strength and post pouring concrete tensile strength also shows strong correlation.(2) Deduced formulas for calculating the moment in the ultimate bearing state; developed laminated surface effect coefficient of bearing capacity of anchor bar.(3) There are limitations to apply the stiffness formula of short-term for calculating stiffness of slab; comparing different stiffness calculation formula, some useful conclusions are obtained; based on the sub structure theory, deduced a equivalent stiffness calculating formula for the lattice girder.(4) Proposed a improved bond slip constitutive model, and verified the reliability of the model through the numerical simulation. (5)12pieces of superimposed slab tests and finite element analysis results indicate that: The superimposed floor slabs without additional constraints have a certain carrying capacity before occurring brittle fracture; the lattice girder restraint can ensure the effective force transformation high ductility, the bearing capacity of superimposed slabs depends on the bearing capacity of joints section.(6) The numerical results agree well with experimental results, which shows that the reliability of numerical simulation method in the paper; numerical analysis results show that the addition of spring element model is not big to the bearing capacity and stiffness influence, but has obvious effect on Crack propagation.(7) This paper proposes a new enhanced integral joint connection pattern for superimposed slab, test results show that:the connection form can strengthen the section stiffness in joint and increase bending capacity of the slab.