Mouli and Khelafi 2007

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This paper concentrates on the bond strength and axial capacity of concrete filled steel columns. A series of tests was performed on rectangular section CFT to consider the behavior of short composite columns under axial compressive loading. The CFT columns were filled with normal and lightweight aggregate concrete where natural pouzzolan was used as the lightweight aggregate component. The main objective of these tests was to clarify the performance of the lightweight aggregate-concrete filled steel specimens compared with those manufactured from normal concrete. The experimental investigations included tests on short steel and short composite columns.

Experimental Study, Results, and Discussion

Two steel sections were used in the tests, a 120 by 80 mm rectangular section and a 150 by 100 mm rectangular section, both 5 mm thick. Two kinds of concrete, normal and lightweight concrete were used to fill the steel sections. For each steel section-concrete mix combination three 100 mm long and three 200 mm long CFT columns were used for axial compression tests and three 550 mm long CFT were used to investigate bond strength between concrete filling and the steel section. For the bond strength specimens, 50 mm of tube was left unfilled and the tube was placed upside down with the unfilled section on the bottom. An axial force was then applied to the center of the concrete fill by means of a steel loading pad about 10 mm smaller than the inside dimensions of the steel section. Recordings of concrete displacement versus applied force were then taken. The 100 and 200 mm CFT were tested by means of axial compression.

The lightweight concrete was found to have a much stronger concrete-steel bond than the normal concrete; the strength of the lightweight concrete bond was about twice as much as that of the normal concrete bond. This was attributed to the different shrinkage strain exhibited by the lightweight and the normal concretes at the same age. The type of concrete did not greatly affect the shape of the load-slip curves. The higher bond strength developed by the lightweight concrete would be beneficial in relation to the performance of composite constructions especially in cases where longitudinal shearing stresses are likely to be predominant. In all axial compression tests, failure took place be the outward bulging of the bigger outer dimensions followed be that of the smaller outer dimensions due to the outward push of the concrete. The results of the investigation showed that the structural efficiency of lightweight aggregate concrete to the squash load is considerable.

References

Mouli, M. and Khelafi, H. (2007). "Strength of short composite rectangular hollow section columns filled with lightweight aggregate concrete," Engineering Structures, 29 (8) ,pp. 1791-1797. doi:10.1016/j.engstruct.2006.10.003