| More and more high-rise steel buildings and large span steel structures were built in China. A plenty of new materials of high strength structural steel were produced to meet the requirements for easy weld ability, seismic behavior and low-temperature impact resistance. In order to reach the advanced world level, series of GJ structural steel with Chinese characteristics has been researched. It has excellent mechanical performance such as proper yield ratio, carbon equivalent, excellent performance in Z direction, thus it can be a good choice instead of imported steel.The carrying capacity of steel structure decreased with the increasing temperatures and so many steel structures destroyed in fire accidents. Hence, the research of the performance for the steel structure at high temperatures is so important to prevent the fire accidents. Gao Jiangang has better fire-resistant performance on account of controlled rolling and cooling process, lower content of C, S, P micro alloy element content.The mechanical properties of Q460 GJ at elevated temperatures and the bearing capacity and deformation of the steel beam used Q460 GJ in fire conditions were studied in the thesis, and the main contents and conclusions are listed as follows:(1) Material experimental study: The tensile tests for the plate specimens with the thick of 8 mm and 10 mm of Q460 GJ steel were conducted at the temperatures of 20?, 100?, 200?, 300?, 400?, 500?, 600?, 700?, 800? and 900?. Three tests were conducted at each temperature and the stress- strain relationship curves, further yield strength and ultimate strength were obtained in this study. The initial elastic modulus of Q460 GJ at different elevated temperatures were obtained by the resonance method. The experiment results of the test were also compared with the current standards and relative test results of mild steel and high strength steel S460.(2) Theoretical analysis of the flexural member in fire conditions: The calculation method for the fire resistance of flexural member, the catenary action and deformation of restrained steel beam at high temperatures, the axial force and trends of mid span deflection and large deformation equation of restrained steel beam were introduced in the thesis.(3) Finite element analysis of mild structural steel beam in fire conditions: The finite element software ABAQUS was adopted to establish the finite element model of simply supported beam and restrained steel beam in fire conditions. Compared with the available foreign experimental results, the reliability of the finite element model at high temperatures can be verified.(4) Parameter analysis of Q460 GJ steel: The finite element model of steel beam was established by using ABAQUS. Compared with the test results of Xiong Gang from Chongqing University, the reliability of the finite element model at room temperature can be verified. Using the method for establish the model of mild structural steel beam at high temperatures to establish finite element model of Q460 GJ beam, and the influence of analysis of critical temperature and critical load of simply supported beam at steady and transient state were considered in the thesis. The influence of critical temperature, axial and rotational restraint stiffness, span-depth ratio, yield strength were also considered in the thesis. Compared with the deformation curves at different situations of restrained steel beam with the cures obtained from Yin's and Dwaikat's paper, the validity for the analysis results of the finite model can be verified.The innovation of the thesis: 1) The strength and rigidity experimental data of Q460 GJ at elevated temperatures were obtained; 2) Employ ABAQUS finite element modle analyze the mechanics mechanism and deformation of simply supported beam and restrained steel beam under high temperature which verify the correctness of the analysis model; 3) Using ABAQUS finite element model analyze the ultimate bearing capacity of Q460 GJ steel beam at room temperature and compared with experiment results of Xiong Gang from Chongqing University; 4) Using ABAQUS finite element model analyze the deformation and mechanism of Q460 GJ steel beam at high temperatures and compared with theoretical formula of Dwaikat and Yin. |
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