Kawano and Matsui 1988

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In this paper, an experimental study to investigate the behavior of circular HTs and CFTs under repeated axial loading was presented. In addition, the response of the frames having tubular bracing members was examined analytically.

Experimental Study

The specimens were simply supported at the ends. Two loading schemes were selected. In the first one, the axial load was applied with repeated large amplitude axial deformation and a repeated axial load with gradually increasing amplitude was applied in the second loading scheme. The specimens had a D/t ratio of 28.9. The measured compressive and tensile yield strengths of the steel tubes were 45.67 and 48.51 ksi, respectively. The measured concrete compressive strength was between 4.75 and 5.08 ksi. The range of the L/D ratio was 6.81 to 40.88.

Failure mostly occurred when the second loading scheme was applied. The failure location was at the mid-length and the failure pattern was cracking of the steel tube. For the CFT specimens, cracking occurred at the crest of the local buckling bulges. The hollow tubes cracked at earlier stages of loading, with cracking occurring in the corners of the tube. For the CFT specimens having an L/D ratio less than 40.88, the yield strength was larger than the buckling strength. The CFT specimens exhibited better response than the hollow ones under both of the loading schemes. The concrete infill delayed local buckling and cracking of the steel tube. The energy dissipation of the CFT members was up to 3.2 times that of the hollow tube specimens.

Analytical Study

The behavior K-braced portal frames made up of tubular braces was investigated theoretically. Two types of frames were analyzed. The first type had a beam hinged at the middle where the braces were connected. For this type of frames, the CFT and HT braces underwent buckling and the frames exhibited rapid deterioration in strength. However, the CFT braces improved the behavior under repeated horizontal loading. In the second type of frames, the beam was hinged at mid-length. In this case, CFT braces achieved a more stable behavior compared to HT braces and no deterioration in strength was obtained.

References

Kawano, A. and Matsui, C. (1988). “Experimental Study on Hysteretic Behavior of Concrete Filled Tubular Members under Repeated Axial Loading,” Proceedings of the Ninth World Conference on Earthquake Engineering, Tokyo-Kyoto, August 2-9, 1988, 9WCEE Organizing Committee, Japan Association for Earthquake Disaster Prevention, Tokyo, Vol. IV, pp. IV-133 - IV-138.