Study On Fire Resistance Of Two-way Concrete Slabs With One-way In-plane Constraint

At present, most reinforced concrete slab fire resistance test does not take into account the in-plane constraint, concrete slab can be in the plane of the free swelling deformation, however, the fire resistance performance of slab in the actual structure will affected by the constraints in the adjacent components in the structure. Therefore, it is necessary to carry out the research of the anti fire performance of the concrete two-way slabs, and then analyze the influence of the surface restraint function on the fire resistance of the concrete floor.In this paper, the test furnace was reformed and developed. The test of fire resistance of three concrete two-way slabs is carried out, and one of them is simply supported slabs, two of them are two-way concrete slabs with one-way in-plane constraint, that is, the constant in-plane constraint force is imposed on the edge of the slab. Comparative analysis of fire behavior of three slabs cracking process and failure mode, temperature, plane and displacement and angle plate outer planar constraint force, The influence of in-plane constraint force on the fire resistance of reinforced concrete slabs is studied. The research results show that the in-plane constraint force has an important influence on the deformation and deformation rate of the plate, and in-plane constraint force greater, the deformation is large, the deformation rate is fast; in the corner region should be reinforced, help to plate film development effect, the increase in the fire resistance performance.Based on the conventional temperature theory, the effect of moisture clog was taken into account by introducing the correction factor of moisture, and the nonlinear finite element program was developed for the temperature of the concrete slabs. The developed program was be used to analyze the effect of correction factor on the temperature of the concrete slabs. The comparison shows that the theoretical results are in good agreement with the tests, when the correction factor of moisture is 2.0. Within the range of engineering application, effect of parameters including thermal conductivity, evaporating temperature, the emissivity, and the initial density of concrete and the convection coefficient, on the temperature of the concrete slabs was analyzed. Results show that the thermal conductivity is the main factor, and the emissivity of exposed surface is the secondary factor as well as the convection coefficient of unexposed surface. The evaporating temperature has an important effect on the temperature plateau of the slab’s unexposed surface. The initial density of concrete, the convection coefficient of exposed surface and the emissivity of unexposed surface have less influence on the slab’s temperature.Based on the yield-hinge line theory of two-way reinforced concrete slabs, this paper presents the model of ultimate bearing capacity under fire of two way slab which incorporated the effect of in-plane constraint and tensile membrane action. In this paper, the ultimate bearing capacity of Confined concrete two-way slabs under fire is analyzed by the model. The results show that in-plane constraint force will have an adverse effect on the ultimate bearing capacity of the slabs.