Kamba, Kanatani, and Tabuchi 1991

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The panel zone behavior in moment-resisting CFT frames was studied in this research. Monotonic tests were conducted on square HT and CFT beam-to-column connections having through diaphragm details. The strength and rigidity of the panel zone was monitored throughout the test. Furthermore, the authors proposed equations to estimate the elasto-plastic behavior of joint panels.

Experimental Study, Results and Discussions

The test setup consisted of a column having a through-diaphragm joint at mid-height. For the CFT connections, only the joint region was filled with concrete. The specimens were designed for failure to occur in the panel zone. Two series of tests were conducted. For the specimens in the first series, the panel zones were annealed, while cold-formed tubes were used in the second series. The main parameter of the tests was the D/t ratio, which was varied from 27 to 48. The range for the yield strength of the steel tube was 48.38 to 52.65 ksi and 54.07 to 56.92 ksi for the annealed and cold-formed specimens, respectively. The compressive strength of the concrete was 3.37 ksi in the first series and 3.56 ksi in the second series.

The failure of the hollow panel zones was due to shear buckling. The concrete-filled panel zones exhibited bending failure as a result of excessive shear deformation. The yield shear force (Q_y) was defined as the shear load when the stiffness decreased to one third of its initial value. The ultimate shear force (Q_u) was taken as the shear load at failure. It was found that the Q_u/Q_y ratio decreased as the D/t ratio got larger for the specimens with hollow panel zone. On the other hand, in the case of the concrete filled panel zones, Q_u/Q_y</math> value was greater for large D/t ratios. Eliminating residual stresses caused an increase in Q_u/Q_y ratio for the hollow panel zones. In addition, it enhanced the deformation capacity. The initial rigidity of the concrete-filled specimens was found to decrease after concrete cracking. However, the specimens continued to exhibit stable behavior as the steel tube limited the concrete deformation. After the shear stress of concrete reached to 50-60% of its compressive strength, the shear strains started to increase while the shear stress remained constant.

Analytical Study

Tri-linear load-deformation curves were proposed for the steel tube and concrete parts of the panel zone. In both cases, it was assumed that shear stress remained constant after it reached its maximum value. The two load-deformation curves were then superimposed. The theoretical results approximately estimated the experimental behaviors. The authors recommended more research to be done for the load-deformation behavior of the hollow tube specimens.

References

Kamba, T., Kanatani, H., and Tabuchi, M. (1991). “Strength and Rigidity of Joint Panel of Concrete Filled CHS Column-to-Beam Connections,” Proceedings of the Third International Conference on Steel-Concrete Composite Structures,” Wakabayashi, M. (ed.), Fukuoka, Japan, September 26-29, 1991, Association for International Cooperation and Research in Steel-Concrete Composite Structures, pp. 189-194.