HIGH TEMPERATURES INFLUENCE ON THE REINFORCED CONCRETE PANELS STRENGTH THROUGH THE LIMIT ANALYSIS THEORY

Resumo

The constitutive behavior of reinforced concrete (RC) structures is significantly altered when
exposed to high temperatures. The high thermal gradients cause deterioration of the thermo-mechanical
properties of the materials together with thermal-induced deformations, which in turn modify the
geometry of the structure. The aim of the present work is to evaluate the influence of fire occurrence on
the stability of the RC panel structures, through the limit analysis theory. By modelling the panel as a
beam, determining the interaction diagrams for each time of fire exposure is the first step. The
temperature profiles along the sections of the panels are obtained numerically and the interaction
diagrams by integrating the concrete and steel strengths along the section with explicit account for the
different parameters controlling the problem, such as the section thickness, reinforcement area and
concrete compressive strength. The second step consists in determining the deformed configuration of
panel and associated distribution of axial and bending moment efforts, considering the second order
effects caused by the eccentricity of the self-weight load induced by the thermal deformations. This is
achieved by analyzing the thermo-elastic equilibrium of the panel under the combined action of thermal
gradient induced by fire and self-weight loading. The analysis is done by overlapping the interaction
diagrams of the sections and the distribution of internal efforts along the structure. Several numerical
examples are presented to assess the effect of relevant parameters on the overall fire safety of the
structure, emphasizing the effectiveness of the approach for design purposes.