Conference Paper

A CONTINUUM-MECHANICAL MODEL FOR FE-SIMULATIONS OF STEEL COSTRUCTIONS IN FIRE

Conference: Structures In Fire 2012

ABSTRACT

This paper presents a thermoviscoplastic constitutive model within the framework of continuum mechanics for the description of the behavior of structural steel subjected to fire loading. The model is represented through a set of ordinary differential equations and belongs to the class of so-called unified theories which do not separate plastic and creep strains. The material parameters are identified for the structural steel S 235 on the basis of tension and compression tests at constant temperature with varying strain rates and verified against transient creep test with varying temperature. For effective numerical simulations with the finite element program ABAQUS the model is prepared with a stress algorithm and consistent tangent operator. The simulations are compared with experimental data of fire resistance tests on columns. 1 ITRODUCTIO For the design of steel structures in fire the common material model of EC3-1-2 [1] is formulated as an one-dimensional rate-independent relationship between stress and mechanical strain. It can be shown that the material behavior of carbon steel is well described for monotonically increasing temperatures and constant loading. But in case of fire, structures are also exposed to varying thermal and mechanical boundary conditions requiring additional considerations. For the simulation of these processes a model should be chosen that exhibits inelastic properties and is capable to describe creep and relaxation at any heating or cooling condition. Therefore, a thermoviscoplastic material model for the simulation of structural steel members under fire conditions has been developed.

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