دانلود رایگان مقاله انگلیسی تحلیل عددی رفتار سازه های پر شده با بتن، ستون های بتن آرمه فولادی (CFSTRC) - اشپرینگر 2017

Abstract

The structural behaviors of concrete filled steel tube reinforced concrete (CFSTRC) columns, which were exposed to a 3- side fire were discussed by using the non-linear finite element analysis (FEA) software ABAQUS. Details of the temperature distribution, fire resistance, failure modes, redistribution of internal force, contact stress between the steel tube and the concrete (both inside and outside of the steel tube), and the development of stress and strain within the CFSTRC columns subjected to a 3-side fire were revealed. The factors that may have affected the fire resistance of the CFSTRC columns exposed to threeside fire were analyzed. Based on the above research, the present study observed uniaxial symmetry on the cross-sectional thermal distribution of the CFSTRC, wherein a significantly lower temperature on the unexposed side was observed as compared to the exposed side. The two side verges of the surface, which were not exposed to fire, exhibited the lowest temperature. Following the end of the heating, the maximum temperature difference reached about 1065o C. The large temperature difference would bring non-uniform thermal stress and strain, and accidental eccentricity. In addition, the existence of concrete inside and outside of the steel tube prevented the steel tube from occurring local buckling, and the failure modes of CFSTRC columns acted as overall bucking. Parameters such as the fire load ratio, sectional dimension, slenderness ratio, sectional core area ratio, and external concrete compression strength significantly influenced the fire resistance of the CFSTRC columns. Finally, a simplified calculating formula was proposed to calculate the fire resistance influence factors of the CFSTRC columns subjected to three-sid fire. The formula-calculated results were well in agreement with the finite element analysis results, thereby providing a simple and feasible method for evaluating the fire-resistance design of these types of components in practical engineering.

6. Conclusions

The present study characterized the mechanical behavior of concrete filled steel tube reinforced concrete (CFSTRC) columns subjected to 3-side fire. Based on the research stated in the paper, the following conclusions can be drawn: (1) The CFSTRC columns subjected to 3-side fire exhibited a mono-symmetrical thermal distribution and a significantly lower temperature on the side unexposed to fire as compared to the surface exposed to fire. At the end of the heating, the maximum temperature difference can reach as high as 1065o C. The large temperature difference resulted in non-uniform thermal stress and strain in the cross section, thereby generating an eccentric rotation of intensity at the center of the cross section. (2) The existence of concrete inside and outside of the steel tube effectively prevented the generation of local buckling within the steel tube. In addition, the failure modes of the CFSTRC columns exhibited overall bucking after the column reached its fire endurance. (3) The fire load ratio, cross-section size, slenderness ratio, section core area ratio, and exterior concrete compression strength significantly affected the fire resistance of the CFSTRC columns under three-side fire.. (4) A simplified calculation formula for the fire resistance of the CFSTRC columns under three-side fire was proposed based on the analysis of the parameters. The simplified calculation results were verified using the finite element analysis results, wherein the validation indicated that the simplified calculation formula provided a more convenient and feasible method of computing the fire resistance of the component under three-side fire. These results can be referenced for fire resistance designs in practical engineering.