Inai et al. 2004

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This paper presents tests results of CFT columns subjected to combined axial load and cyclic shear. The objectives of the tests were to study the cyclic load deformation behavior and determine ultimate strength and deformation capacity of CFTs.

Experimental Study, Results, and Discussion

The main test parameters were tube shape (square and circular), D/t ratio, strength of steel and concrete, axial load ratio P/Po, and loading angle for biaxial bending. Thirteen circular and twenty square CFTs were subjected to axial load and cyclic shear load. The D/t ratio of the specimens varied between 17.8 and 53.3. The ranges for the measured yield strength of steel and measured compressive strength of concrete was 58.0-113.1 ksi and 5.80-13.05 ksi, respectively. The L/D ratio was 6 for all of the specimens. Axial load was varied from 0.7  Po to negative 0.3 x Po for four circular and four square specimens, and was held at 0.4 x Po for the rest of them. The test setup simulated fixed end conditions and induced double curvature in the specimens. Cyclic shear loading was displacement controlled. Square steel tubes were built of two channel sections by welding, while channel sections were cold formed from flat plate. No annealing of steel tube was reported; thus the steel tube was likely to have residual stresses due to both cold forming and welding. Moment-chord rotation and rotation-axial strain diagrams were shown in the paper. The rotation capacity of square CFTs was observed to be larger for higher steel strength, smaller D/t ratio, and smaller concrete strength, with loading angle effect being unclear. No clear effect of these factors on the circular CFT rotation capacity was observed.

Axial strain of the square CFTs having a constant axial load was higher for higher concrete strength, lower steel strength, and larger D/t ratio. Effects of steel strength and D/t ratio on square specimens with variable axial load were unclear. Axial strain in biaxial bending was lower than in uniaxial bending. For circular CFTs having a constant axial load, the value of axial strain was higher for lower steel strength, lower concrete strength, and larger D/t ratio, while the influence of steel strength and D/t ratio was unclear for circular specimens with variable axial load.

Analytical Study

Maximum strength of all specimens plotted against the interaction diagrams calculated for ideal full plastic state of stress was shown in the article. Experimental strength exceeded the interaction diagram values, except for several specimens with a variable axial load.

Several conclusions were drawn by the authors. The rotation capacity and axial strength of circular specimens exceeded those of square specimens. Axial strain was larger for square specimens. Rotation capacity and maximum strength were smaller for the variable axial load specimens, and were not affected by the loading angle.

References

  • Fujimoto, T., Nishiyama, I., Mukai, A., and Baba, T. (1996). “Test Results of Concrete Filled Steel Tubular Beam-Columns,” Proceedings of the Third Joint Technical Coordinating Committee Meeting, U.S.-Japan Cooperative Research Program, Phase 5: Composite and Hybrid Structures, Hong Kong, December 12-14, 1996, National Science Foundation, Arlington, Virginia.
  • Inai, E., Mukai, A., Kai, M., Tokinoya, H., Fukumoto, T., and Mori, K. (2004). “Behavior of Concrete-Filled Steel Tube Beam Columns.” Journal of Structural Engineering, ASCE, 130(2), 189–202. doi:10.1061/(ASCE)0733-9445(2004)130:2(189)