Behaviour of restrained concrete filled square double-skin and double-tube hollow columns in case of fire

摘要

This paper presents the results of an experimental investigation on the fire behaviour of restrained composite columns made with square concrete filled double-skin and double-tube hollow sections. In the fire resistance tests the columns have been tested for different parameters that may influence their behavior, as for example the type of cross-section, the concrete filling of the tubes (ordinary, high-strength and light-weight concrete), the load level and the stiffness of the surrounding structure to the testing columns. These columns had two concentric steel tubes, where the inner one had approximately half the side of the outer one. The double-tube columns had both tubes filled with concrete and the double-skin ones had only concrete between tubes. As major conclusions, it was observed that the load level had a small influence on the reduction of the critical times but some influence on the reduction of the ultimate collapse times of the tested columns. The stiffness showed an insignificant influence on the critical time but again a higher influence on the ultimate collapse time of the columns being those smaller for the higher stiffness values. The concrete infill showed some influence, presenting the columns with high-strength concrete in the inner tube higher ultimate collapse times than those with ordinary concrete. The use of light-weight concrete between tubes did not show advantages when comparing with the ordinary concrete. The double-tube columns presented in general advantages over the double-skin columns being the ultimate collapse times of the first higher than those of the second.