Nakahara and Sakino 1998

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The authors investigated the behavior of square steel tubes filled with high strength concrete. An experimental study including monotonic tests of eight stub-columns and eight beam-columns was described.

Experimental Study, Results, and Discussions

The test specimens were filled with concrete having a measured compressive strength of 17.26 ksi Steel tubes with measured yield strengths of either 44.96 ksi or 113.28 ksi were utilized. Two channel sections were welded to each other toe-to-toe to manufacture the steel tubes. All the specimens were square and had an L/D ratio of 3. The D/t ratio was either 30 or 60. Four hollow steel tubes and four CFTs were subjected to axial compressive loading. The hollow columns showed a more dramatic drop in strength after achieving their peak strength as the D/t ratio got larger. None of the CFT columns reached their squash load capacity, due to the onset of local buckling .

Uniform bending and constant axial load was applied to the beam-column specimens. The main parameters of the beam-column tests were the D/t ratio and axial load ratio. Bending was provided through thick and stiff end plates welded to the specimen. The beams were thus simply supported, with rotations applied to their ends . The welded joints between the steel tube and end plates were reinforced with 1.31 in. thick trapezoidal plates. These plates were attached to the tension face of the tubes at the ends of the tubes. When the tests were conducted, it was observed that the specimens again saw a shaper drop in strength after achieving the peak strength with an increase in D/t ratio or axial load ratio. For most of the specimens, the experimental moment capacity was less than the plastic moment capacity.

During both series of the tests, the authors observed early concrete crushing and local buckling. Also, the scale effect of the cross section and difference of steel and concrete strains at maximum strength were among the factors affecting the test results.

References

Nakahara, H. and Sakino, K. (1998). “Axial Compressive and Uniform Bending Tests of High Strength Concrete Filled Square Steel Tubular Columns,” Proceedings of the Fifth Pacific Structural Steel Conference, Seoul, Korea, October 13-16, 1998, pp. 943-948.