Determination of the ULS, for columns with small dimensions, under biaxial bending and symmetrical fire conditions

Abstract

Determination of the ULS, for columns with small dimensions, under biaxial bending and symmetrical fire conditionsDeterminação do ELU, para pilares com pequenas dimensões, sob flexão composta oblíqua e incêndio simétrico Abstract ResumoObtaining internal load capacity, in reinforced concrete sections, at ambient temperature, under biaxial bending, is one of the most common tasks done by structural engineers, but not so common when the member is in fire situation. The intention of this paper is to show that is possible to correlate the ultimate limit state (ULS), in fire situation, with ULS at ambient temperature, for square cross sections under fire from all faces. To reach the purpose and give support to the numerical analysis of this article, a computer program, in Delphi language, called COL FIRE, is being developed by the authors. Keywords: fire, columns, ultimate limit state, ULS, interaction diagram.A obtenção dos esforços internos resistentes, em seções de concreto armado, à temperatura ambiente, sob flexão composta oblíqua, é uma das tarefas mais comuns realizadas por engenheiros de estruturas, mas não tão comum quando o elemento está submetido a ação de incêndio. O objetivo deste artigo é ilustrar que é possível correlacionar o estado-limite último (ELU), em situação de incêndio, ao ELU à temperatura ambiente, para seções quadradas sob incêndio em todas as faces. Para atingir o propósito e dar suporte à análise numérica deste artigo, um programa de computador, em linguagem Delphi, chamado COL FIRE, está em desenvolvido pelos autores.Palavras-chave: incêndio, pilares, estado-limite último, ELU, diagrama de interação.

Computational algorithm for the verification of reinforced concrete sections in fire situation

“…Alternatively to the diagram proposed by ABNT NBR 15200:2012 [36], according to previous studies conducted by Albuquerque et al [15] and Moreira et al [17] with satisfactory results, it can be used the parabola-rectangle diagram of ABNT NBR 6118:2014 [35], considering the strength of concrete adapted to high temperatures, as follows: (16) in which ε c2 is the specific compressive strain of the concrete at reaching the maximum strength, and ε cu is the ultimate compressive strain (rupture), both indicated in Table 1.…”

“…In order to evaluate the M y × M x interaction diagram in fire situation, a comparison was made between the numerical analysis developed by Cherem and Silva [16] and the results obtained by Pisafo for the same problem. Cherem and Silva [16] analyzed a concrete column of 30 × 30 cm², using a concrete with f ck of 30 MPa and 8 CA50 steel bars with a diameter of 10 mm and with a 30 mm of concrete cover. The fire analysis considered the standard fire curve of ISO 834-1:1999 [21] with a fire time of 90 minutes, a moisture content of 4 % for concrete and all faces exposed to fire (Figure 12).…”

“…Silva [16] and by Pisafo. The "Advanced method" [16] consists of obtaining the maximum strength of the section using the stressstrain curves proposed in ABNT NBR 15200:2012 by means of an algorithm that varies the strain in the center of gravity of the section and the curvatures around of the x and y axes, without limiting the maximum strain in the materials [36].…”

“…Silva [16] and by Pisafo. The "Advanced method" [16] consists of obtaining the maximum strength of the section using the stressstrain curves proposed in ABNT NBR 15200:2012 by means of an algorithm that varies the strain in the center of gravity of the section and the curvatures around of the x and y axes, without limiting the maximum strain in the materials [36]. The "Reduction factor" [16] is an analytical method proposed by the authors, which consists of adjusting the M y × M x interaction diagram at room temperature for a reasonable approximation in a fire situation, without the need for thermal analysis.…”

“…To avoid further material losses and especially lives, research in the field of fire has intensified more and more. Experiments with the goal of investigating the behavior of reinforced concrete elements subjected to high temperatures [2,3,4,5], researches for the analysis of thermal and thermomechanical problems of structures [6,7,8,9], studies that have investigated and provided simplified [10,11,12,13,14] and alternative [15,16,17] methods for design and verification of reinforced concrete elements have been performed in recent times. Studies on design up to that time were limited to analyzing rectangular sections of reinforced concrete in fire situation, comprising only normal composite bending.…”