Experimental Research On Mechanical Behaviors Of Reinforced Concrete Columns After Exposure To High Temperature And Long-term Load

Due to the increasingly fire danger to structure, researchers started to study the behaviors of concrete under high temperatures and fire resistance as well as the mechanical properties of unconstrained concrete members and structures under high temperatures. But few researchers have considered the effects of the initial load and the long-term load after high temperatures during the tests, which did not match with the actual loading condition of structures under high temperatures and long-term load. Without consideration of constrained stress, the reinforced concrete structures would not give the correct response after the interaction of high temperature and long-term load. So the current study could not give the right damage assessments and reinforcement schemes for reinforced concrete structures under fire and long-term load. Therefore, in this paper, the mechanical properties of axially restrained reinforced concrete after high temperature and long-term load were researched.The main work was summarized as follows:(1) Experimental study on the mechanical properties of concrete with sustained restrained stress after experiencing a process of heating, cooling and long-term load. The main focus of this study was the effects of load duration and temperature grade on the deformation of concrete under long-term load as well as the residual compressive strength, elastic modulus and stress-strain relation after the whole period.(2) Experimental study on the mechanical properties of reinforced concrete with sustained restrained stress after experiencing a process of heating, cooling and long-term load. The main focus of this study was the effects of load duration and temperature grade on the deformation of reinforced concrete under long-term load as well as the residual compressive strength, axial stiffness and stress-strain relation after the whole period.(3) Based on a simplified calculation model of creep and shrinkage and the age-adjusted effective modulus method, a calculating method of axial deformation of reinforced concrete under long-term load was proposed. And a shrinkage and creep model of concrete under high temperature was also proposed on the basis of the axial deformation from concrete test at room temperature. The axial deformation of concrete and reinforced concrete after high temperature was calculated through numerical analysis. (4) On the basis of the constitutive models and residual compression strength models, the concrete stress-strain model under long-term load was proposed. Then, through numerical analysis, the stress-strain curves of concrete and reinforced concrete after high temperature and long-term load were calculated.