Research On Post-fire Performance Of Steel-Concrete Composite Beam-Column Joints

Steel-concrete composite structures have been widely used in construction projects in recent years. It is very important to study the performance of steel-concrete composite beam-column joints subjected to a fire including the heating and cooling phases for the structural fire safety design and after-fire evaluation. Concrete filled steel tubular (CFST) colum to composite beam joints and steel reinforced concrete (SRC) column to SRC beam joints, which have been used widely in real projects, are chosen as the research objects. The performance of two types of composite beam-column joints are studied in a life-time loading sequences including initial loading, heating, cooling and post-fire loading.The main research work includes:1. Experiments were carried out on CFST column to composite beam joints and SRC column to SRC beam joints after exposed to heating and cooling fire with initial loads. The temperature distributions, deformations, strains and residual load bearing capacities of joints were analyzed.2. After the determinations of material properties in ambient, heating, cooling and post-fire phases, finite element analysis (FEA) models of CFST column to composite beam joints and SRC column to SRC beam joints were established in ABAQUS, for which, material constitutive relations conversion and steel high-temperature creep modelled using the subroutine. The FEA models can be used to analyze the entire process of the two types of joints under the combined loads and fire including heating and cooling phases. The accuracy of FEA models were verified by the test results including fire resistance tests of SRC columns carried out by the author.3. The temperature distributions, failure modes, deformations, stress and strain distributions, internal force, moment versus rotation angle relations of CFST column to composite beam joints and SRC column to composite beam joints under the combined loads and fire including heating and cooling phases were analyzed using the established FEA models. 4. Influences of parameters, such as heating time ratio, load ratios of column and beam, beam-column linear stiffness ratio, beam-column ultimate moment ratio, steel ratio, concrete strength and steel yield stress on the moment versus rotation angle relations of CFST column to composite beam joints and SRC column to SRC beam joints under combined loads and fire were analyzed. Simplified formulas for calculating the residual stiffness ratio and residual load bearing capacity ratio of the two types of composite joints were proposed.