Study On The Static And Fire Resistance Property Of The Recycled Concrete Filled Steel Tube

Compared with the traditional reinforced concrete members, the concrete filled steel tubes(CFST)are widely used in the practical modern buildings because of its simple form, convenient construction and easy formwork. Meanwhile, with the development of engineering construction, more and more construction waste are produced that seriously restrict both society and economy. Recycled concrete technology is an environmental protection to recycle waste concrete, and it can effectively solve the problem of waste disposal. Compared with normal concrete, recycled concrete has higher porosity, lower strength and higher deformation. In order to make up for these shortcomings, the combined form of recycled concrete filled steel tube( RCFST)is a better chioce. In this thesis, recycled concrete filled steel tube is the research subject and its static and fire resistance property is being studied. This research can provide some basis for its application in the practical engineering.The basic properties of recycled concreted were studied based on the analysis of many test data. The relationship between recycled coarse aggregate replacement and compressive strength, elastic modulus, ultimate strain was established respectively. Thus this paper established a suitable constitutive relation for recycled concrete and verified its applicability through the finite element method(FEM). And this paper also studied the thermal parameters of the recycled concrete, and thus obtained a series of available thermal parameters that provided foundation for following fire resistance research.Based on the unified theory of normal concrete filled steel tube and the “equivalent area”, axial bearing capacity formula of RCFST short columns was derived. Then according to the recycled concrete constitutive relation, finite element model of RCFST was established. Through the comparisons of calculative values and test values, and the comparisons of calculative values and FEM values respectively, the formula was verified. Because the use of existing regulation is not safe for practical design to estimate the stable performance of RCFST, a modified stability factor formula was obtained by using the international database. And the modified stability formula was verified by some experimental data.FEM was used to simulate the real CFST experiment and the results of resistant time proved the reliability of this FEM. We Obtained the law between fire load ratio; hollow rate and the fire-resistant time of RCFST. Based on the average temperature field and the bearing capacity formula of RCFST under room temperature, this paper derived the bearing capacity formula of RCFST columns under high temperature. Since the RCFST columns are still not satisfied with the minimum fire resistance time requirement in domestic relevant norms and standards. This article adopted the way of reinforcement in strengthening the fire resistant properties of RCFST without fireproof coating, and the ultimate bearing capacity formula of bar-reinforced RCFST under high temperature was derived. Finally, this paper anlysized the influence of the ratio of reinforcement and the ratio of steel for the fire resistance, and obtained the reasonable ratio of reinforcement for fire design. This research work can provide a reference for fire resistance design.