Gajalakshmi and Helena 2012
This research investigates the cumulative damage of in-filled steel columns subjected to quasi-static loading. Eight circular CFT columns and eight circular steel fiber reinforced concrete in-filled tube (SCFT) columns of diameter-to-thickness ratio (D/t) 38 and 57 were tested. Phase I testing consisted of benchmark tests on the CFT and SCFT columns under variable amplitude loading combined with constant axial load to establish the hysteresis behavior. Phase II testing consisted of tests on CFT and SCFT columns under constant amplitude loading histories focused on the effects of amplitude and the number of cycles on damage accumulation.
Experimental Study, Results, and Discussion
Eight CFT and eight SCFT columns were constructed that were 39.37 inches and seam welded. All of the specimens were welded and strengthened with four numbers of 0.24 inch thick gusset plates at the bottom to ensure a strong connection with the footing. The columns were fixed at the bottom. Eight specimens had 4.49 inch diameters and 0.079 inch tube thickness and eight specimens had 4.49 inch diameters and 0.118 inch tube thickness. The concrete in the CFT columns had a compressive strength of 4.70 ksi and the steel fiber reinforced concrete in the SCFT columns had a compressive strength of 8.38 ksi. The steel used for the columns had a yield strength of 42.5 ksi.
A cyclic lateral load was applied 33.46 inches from the base of the specimens and a constant axial load was applied to the specimens. In the first phase, variable drift amplitude tests were carried out by applying three single lateral loading cycles corresponding to an increment of 0.25% peak drift ratio. The loading procedure was continued until failure of the specimen. Failure of the columns was defined by ruptured of the steel tube at the plastic hinge location leading to a visible crack in the tube and a drop in the peak lateral force by over 20%. In the second phase lateral cyclic load at constant drift ratios of 2%, 4%, and 6% were applied to the specimen.
A simplified cumulative damage model for CFT and SCFT columns was proposed in conjunction with the application of Miner’s linear damage accumulation rule provides a reasonable estimation of the damage index. The SCFT columns exhibit higher energy absorption capacity, enhanced ductility, and reduced damage indexed compared to the CFT columns. The experiment also revealed that the energy capacity of a member at failure is dependent on the drift amplitude.
Reference
Gajalakshmi, P., and Helena, H. J. (2012). “Behaviour of concrete-filled steel columns subjected to lateral cyclic loading.” Journal of Constructional Steel Research, 75, 55–63. doi:10.1016/j.jcsr.2012.03.006