Abstract
ABSTRACT For the dimensioning of structural elements in fire situation, simplified equations and parameters are commonly used in analytical equations or numerical models. More complex equations or simplified values can be chosen by the designer for determine materials properties in high temperature in numerical models, however, numerical modeling can be quite sensitive to the variation of some of the physical and mechanical properties. In this paper, the sensitivity of the numerical model in relation to the values according to the level of simplification chosen was evaluated, presenting an analysis in relation to the results found to contribute to the choice of these parameters and presenting the indications found in the literature. In this sense, this work presents a study of sensitivity to the variation of the values of steel and concrete properties, presented in the Eurocode and Brazilian standards, in addition to the moisture content and emissivity of the surface exposed to fire, for the dimensioning, in a fire situation, of steel tube columns, of circular and square section, filled with concrete. The studies were carried out via numerical modeling developed in the software ABAQUS. It was verified that the resulting emissivity values equal to 0.7 or 0.8, recommended in the literature, are conservative, and the choice of either does not bring significant changes in the temperature field obtained for the structural elements under analysis. It was also verified that the concrete moisture content is a relevant aspect for the formation of its temperature field, also affecting, but to a lesser extent, the steel temperature. Regarding the physical and mechanical properties of the materials, this sensitivity study suggests the adoption of the values from the equations presented in Eurocodes, without simplifications, and with the specific heat and thermal conductivity of the concrete, adopted in accordance with the Eurocode 4.
Highlights
The columns made of steel tube, of circular and square section, filled with concrete, are usually dimensioned for a fire situation by simplified equations of practical application, presented in the literature [1], [2] and in normative codes, such as EN 1994-1-2 [3] and ABNT NBR 14323: 2013 [4]
In the case of steel tubes filled with concrete, the interaction between both materials increases the complexity of the problem, so that the temperatures usually obtained from graphs and tables presented in the literature [2] are not suitable for any type of situation
The effect of the moisture content in the concrete is usually considered in the numerical models by values of the specific heat obtained by Equation 7 or 8, considering Cc, peak as a peak value, which occurs between 100 °C and 115 °C, decreasing linearly between 115 °C and 200 °C
Summary
The columns made of steel tube, of circular and square section, filled with concrete, are usually dimensioned for a fire situation by simplified equations of practical application, presented in the literature [1], [2] and in normative codes, such as EN 1994-1-2 [3] and ABNT NBR 14323: 2013 [4]. Materials properties at high temperature The thermal properties of steel and concrete considered in the numerical models were from EN 1992-1-2 [5], EN. With respect to the steel elastic modulus at high temperature (Ea, ) its value is determined by Equation 1, whose respective reduction factors are indicated in EN 1993-1-2 [6], EN1994-1-2 [3] and ABNT NBR 14323 [4], as Table 1. The Poisson coefficient of steel and concrete is indicated respective as equal to 0.3 and 0.2, regardless of temperature
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