Numerical model of thermoelastic-plastic concrete material

The objective of the employment of a sophisticated finite element method (FEM) program for structure fire resistance evaluation is to compliment, if not to substitute for altogether, the expensive fire tests of the natural size structural elements. Unfortunately the temperature dependent material options, provided by FEM programs, can be directly applied only to the steel and other materials with the similar hardening behaviour under compression and tension, For such materials as concrete with a hardening under compression and softening (cracking) under tension only cold numerical models exist and they cannot be used for the structure fire resistance evaluation. Instead the temperature dependent concrete model can be created in a separate subroutine and then inserted into the main program. Actually the thermoelastic-plastic concrete material was developed in two versions: first, the experimentally defined temperature functions of compressive and tensile strength. Young's modulus and thermoplastic (transient) strains were used as input data and then the standard thermoelastic stress analysis (ABAQUS) was performed. Second, the temperature dependent strength and Young's modulus were input as previously and the thermoplastic flow was computed in a subroutine following the ABAQUS algorithm for the compressive and tensile stress state taking into account the temperature dependence of the parameters involved. The computed results (displacements) were compared to the measured ones with resonable difference between.