Abstract
Abstract The increase in temperature reduces the strength of steel and concrete, in such a way that it is essential to verify concrete-filled steel tube columns in fire situations. Numerical simulations, with lower costs than laboratory tests, have great importance in checking resistance and defining simplified methods for design practice. However, peculiarities of the thermal and mechanical behavior of heated confined concrete and the air-gap effect (a phenomenon inherent to concrete-filled steel columns) must still be better understood. Therefore, this study presents the development of a numerical model performed in the ABAQUS software (Dassault Systemes SIMULIA Corp., 2014) for the thermomechanical analysis of short columns composed of circular and square concrete-filled steel tubes considering the air-gap effect. The air-gap phenomenon is presented and analyzed according to possibilities of implementation to the numerical model and, finally, the proposed numerical model is validated with experimental results presented in the literature. According to the study results, the numerical model can be used to define and adjust simplified methods for verification of composite columns in fire situation. The importance of considering the air-gap effect in numerical modeling was confirmed, taking into account that disregarding its effect may result in overestimated responses of the steel tube resistance in fire situations. Moreover, it was suggested thermomechanical joint analysis and the use of the explicit solver as a strategy to minimize processing time.
Highlights
This paper presents a three-dimensional numerical model developed in the ABAQUS software (Dassault Systemes SIMULIA Corp., 2014) [16], to perform the thermomechanical analysis of short columns composed of concrete-filled steel tubes of circular and square sections
The presented three-dimensional models and the two-dimensional model, the last being exclusive to heat transfer analysis, provided results close to experimental tests reported in the literature
The two-dimensional model used for specimens of symmetrical geometry and uniform fire action proved to be an effective alternative to determine temperature fields in tubular concrete-filled columns
Summary
The columns composed of tube filled with concrete have proved to be an interesting structural solution in combining the benefits of both materials, including with regard to fire resistance [1], [2] and their use can be observed in buildings and bridge structures [3]–[5]. Ghojel [15] carried out studies on the air-gap effect and presented tests with circular concrete-filled steel tubes specimens, heated in an electric oven to the temperature of 900 °C. This paper presents a three-dimensional numerical model developed in the ABAQUS software (Dassault Systemes SIMULIA Corp., 2014) [16], to perform the thermomechanical analysis of short columns composed of concrete-filled steel tubes of circular and square sections. The specimens considered in this study consist of 500-mm high short columns composed of steel tubes filled with concrete of circular and square sections. The mechanical behavior in the steel-concrete interface connection was defined by a hard contact that allows the separation between the different surfaces and does not allow overlap between them, and by a penalty contact, considering the Coulomb law with a constant coefficient of friction equal to 0.3 (in the literature this value is reported between 0.2 and 0.3) [21]. The response obtained from the explicit solver is considered as an approximation, the dynamic-explicit method leads to a significant reduction in computational effort and to the stability of the analysis [24], [25]
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