NUMERICAL EVALUATION OF LOAD INDUCED THERMAL STRAIN IN RESTRAINT STRUCTURES COMPARED WITH AN EXPERIMENTAL STUDY ON REINFORCED CONCRETE COLUMNS

摘要

This paper presents a new thermal induced strain model for concrete (TIS-Model) [1]. The nonlinear model comprises thermal strain, elastic strain, plastic strain and transient temperature strains as well as load history which means that, as a consequence, the modelling of restrained concrete structures subjected to fire is possible. Calculations of simple elements, namely columns, were done by FE method using the structural code SAFIR [2] in which the material model using the new transient TIS-Model has been incorporated. This code is suitable to calculate complex structures with different material models. The behaviour of reinforced columns with a constant load during heating and cooling was calculated. The results are compared with the results of measured data related to different mixtures of siliceous concrete with compression strength lower or equal than 50 MPa. The calculations showed a good correlation between the TIS-Model and measured data. In addition, a comparison between results using the Eurocode 2 (EC2) material model and the TISModel for concrete structures is given. It was shown that there are differences in the results of structure calculations with both models. The influence of high compressive stresses in concrete section is very high, because the creep strains for transient temperature condition indicates a significant influence of the thermal induced strains. The Eurocode doesn’t consider this behaviour explicitly. According to our results, the time of failure is shorter using the EC2-Model for concrete members under high compressive load or restraint compared to the TIS-Model.