Bergmann 1994
Sixteen tests were performed to investigate the behavior of CFT columns with high strength concrete under various methods of load introduction.
Experimental Study, Results, and Discussion
Sixteen specimens, comprised of four different cross-sections each with four different loading conditions, were tested under monotonically increasing axial load. Of the four cross-sections, two were circular, with diameters of 12.75 in. and 20 in. and thickness of 0.22 in. and 0.25 in. respectively, and two were square, with side lengths of 7 in. and 10.25 in. and thickness of 0.25 in. and 0.28 in. respectively. The four loading conditions were: 40 in. long with load applied to the entire cross-section, 40 in. long with load applied only to the concrete core, 40 in. long with load applied only to a small portion of the concrete core, and 160 in. long with load applied to the entire cross-section. In all but one specimen, the steel had a nominal yield strength of 51 ksi. The one specimen that differed was the 160 in. long specimen with the larger circular cross-section which had a nominal yield strength of 34 ksi. Concrete with a compressive strength of 13.4 ksi was used.
The specimens that were loaded only on a small portion of the concrete experienced local failures at the point of load application and exhibited lower strength than the other specimen. The strength of three of the four specimens with the larger circular cross-section exceeded the capacity of the testing machine and only a lower bound of load was determined. The load deformation curves of the remaining specimens exhibited similar traits. Most notably, upon reaching ultimate load, the strength decreased suddenly, followed by a relatively constant strength.
Reference
Bergmann, R. (1994). “Load Introduction in Composite Columns Filled With High Strength Concrete,” Tubular Structures VI, Proceedings of the Sixth International Symposium on Tubular Structures, Grundy, P., Holgate, A., and Wong, B. (eds.), Melbourne, Australia, 14-16 December 1994, A. A. Balkema, Rotterdam, The Netherlands, pp. 373-380.