engleski

Transient Thermal 3D FE Analysis of Headed Stud Anchors Exposed to Fire

In the present paper a transient three.dimansional thermo-mechanical model for concrete is presented. For a given boundary conditions, temperature distribution is calculated by imploying a three-dimensional transient thermal finite element analysis. The thermal properties of concrete are assumed to be constant and independant of the stress-strain distribution. In the thermo-mechanical model for concrete the total strain tensor is decomposed into pure mechanical strain, free thermal strain and load induced thermal strain. The mechanical strain is calculated by using temperature dependant microplane model for concrete. The dependancy between the macroscopic concrete properties (Yound's modlulus, tensile & compressive strength and fracture energy) and the temperature is based on the available experimental data base. The free thermal strain, which is stress independant, is calculated according to the proposal of Nielsen et al. The load induced thermal strain is obtained by imploying the bi-parabolic model recently proposed by Nielsen et al. It is assumed that the total load induced thermal strain is irrecoverable, i.e. creep component is neglected. The model is implemented into a three-dimensional finite element code. The performance of headed stud anchors exposed to fire was studied. For a given geometry of a concrete member and for a constant concrete properties three-dimensional transient thermal FE analysis was carried out for three embedment depths and for four thermal load histories. The analysis shows that the resistance of anchors can be significantly reduced if they are exposed to fire. The largest reduction of the laod capacity was obtained for anchors with relatively small embedment depth. The numerical results agree well with the available experiments.

concrete; high temperature; 3D finite elements; microplane model; thermo-mechanical model; headed studs

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