On the effect of the boundary conditions of plain concrete exposed to high temperatures under uniaxial compression

摘要

The effect of the boundary conditions, defined as the thermal expansion restraint imposed by the external uniaxial compressive load in plain concrete subjected to high temperatures, is discussed. A numerical mesoscopic investigation uncoupled the load induced thermal strain (LITS) into three main components (aggregates and matrix strain contributions and the effect of the thermal expansion restraint). The analyses demonstrate that LITS depends on the materials properties (viscous-plastic behavior) and also on the boundary conditions, which is function of the test setup and seems to be not related to the material properties. In this paper, the role of the boundary conditions on 1-phase (homogeneous) and 2-phase (matrix + aggregates) numerical analyses are investigated. A LITS semi-empirical model is incorporated in the numerical modeling to account for the stiffness degradation. It is demonstrated that in 1-phase models, the effect of the boundary conditions is absent, which is not true for mesoscale analyses. In this case, the effect of the boundary conditions should be taken into account and subtracted from the results to avoid an over-estimation of the material response. It is important mentioning that the analyses of concrete behavior at elevated temperatures and transient creep experimental procedures completely neglect the role of the boundary conditions.