Analysis Of Thermo-elastic-plastic On Reinforced Concrete Structures Subjected To Fire

The research on fire resistance of reinforced concrete structures is always one of the important issues in solid mechanics and structural engineering field. Because of the limitation of the test equipment and scale, at present the simulation and analysis to the whole structrure is worked out with the finite element methods. The serious internal forces redistribution and the complicated deformation will appear in the reinforced concrete structures applied by fire temperature and external loads. Therefore, the research on fire resistance of reinforced concrete structures is becoming a difficult problem to be solved in academia and engineering field.According to the results about fire resistance of reinforced concrete structures obtained by the scholars at home and abroad, the theoretical research on the mechanical behavior of steel and concrete at high temperature is carried out. Also the nonlinear finite element calculation to fire resistance of reinforced concrete structures is accomplished. The main contents are as follows:1 The theoretical and test results about the mechanical behavior of steel and concrete at high temperature obtained by the scholars at home and abroad are concluded and summarized systemically, which provide a helpful foundation for the thermal and structural analysis on reinforced concrete structures.2 Based on the principle of heat transfer, the finite element iteration equations for the cross-section temperature field of the reinforced concrete members are obtained with the virtual work principle. The calculation procedure for the temperature field of reinforced concrete members is worked out, from which the results is validated by the test results obtained by other scholars. The influence of cross-section size, fire exposure types and fire duration on temperature distribution is discussed.3 Based on nonlinear elastic and thermal elasto-plastic theories, the general thermo-elastic-plastic creep constitutive equation is derived. According to different yield rules the incremental thermo-elastic-plastic creep constitutive equations for steel and concrete are obtained. The algorithms of backward Euler integration and implicit integration are adopted for the numerical simulation to the constitutive equations and the results are validated by test results, which provided a theoretical basis for fire resistance of reinforced concrete structures.4 The reinforced concrete continuous beam is divided by steel bars combination elements. The thermo-elastic-plastic analysis on reinforced concrete continuous beams of two spans subjected to fire and concentrated loads is carried out with the stiffness matrices of steel bars combination elements, and the deflection at midspan is obtained. A computation method for flexural stiffness of double reinforced beam with rectangle section under fire temperature is proposed based on the moment equilibrium condition in the section of reinforced concrete beam. According to the principle of mechanics and the character of material at elevated temperature, the elastic-plastic process of the internal forces redistribution and deformation of reinforced concrete continuous beams of two spans under an elevated temperature and constant load is worked out.5 Based on total Lagrangian formulation, the spatial beam-column element model of reinforced concrete with dual nonliearity of material and geometrey is established. The tangent stiffness matrices of spatial beam-column element model of reinforced concrete under fire condition are derived. The nonlinear analysis of one-bay one-storey reinforced concrete frame under fire is worked out by a nonlinear finite element procedure with initial stress iteration method, and the variation of displacement at partial nodes in the frame is discussed.