A Concrete Model Considering the Load History Applied to Centrally Loaded Columns Under Fire Attack

The description is given of a model for concrete in compression at elevated temperature that incorporates elastic, plastic and creep strains as functions of the temperature and stress history. The plastic strain and the creep strain depend on the stress history and the stiffness of the model depends on the load level during fire exposure. The proposed model is an updated version of a model presented earlier by one of the author [I]. Fifteen fire resistance tests have been performed on reinforced concrete columns centrally loaded under various heating, loading and restraint conditions. From the test results, it can be concluded that the strength of columns during fire is irrelevant to the restraint of elongation, and that the sustained load about 0.15 load level leads to a higher residual strength than the unloaded condition does. A comparison is given between experimental results and computed results. The calculations were performed either with the proposed Schneider concrete model or with the EC4 concrete model. The proposed model is closer to experimental values than the EC4 model when considering longitudinal displacements as well as axial restraint forces.