Nishiyama et al. 2004

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An experimental study on CFT beam-to-column connections was presented. Half-scale internal and external connections were tested under reversed cyclic loading. The performance of the connections manufactured from high strength materials was the main focus of the research. In addition, the connection details and loading conditions varied for the specimens to study their effects. The experimental results were also compared with AIJ-SRC (1997) design code provisions.

Experimental Study, Results, and Discussion

Seven square and four circular CFT beam-to-column connections were tested. The specimens were made up of CFT columns and wide flange steel girders. The steel tubes were manufactured from two channel sections. One connection detail was 3D and the others were 2D. Either through diaphragm or outer diaphragm connection details were used. The thickness of the panel zone webs and flanges were less than that of the webs and flanges of the CFT columns away from the panel zone. This was to encourage shear yielding would take place in the connection rather than at the column. The range of the D/t ratio for the square and circular panel zones were 51 to 55 and 58 to 61, respectively. For the CFT columns, the D/t ranges were 17 to 21 for square shapes and 19 to 31 for circular shapes. The measured yield strength of the steel varied between 63.2 ksi and 110.7 ksi. The measured compressive concrete strength ranged from 7.89 ksi to 15.95 ksi. One exterior and all of the interior connections were subjected to constant axial load. Variable axial load was applied to the remaining exterior connections. The specimens were loaded by antisymmetric cyclic shear forces at the girder ends, and the 3D connection detail was loaded at a 45 degree angle relative to the CFT cross section principal axes.

The panel zone shear strengths calculated by the AIJ-SRC (1997) procedures were less than the experimental shear strengths of the CFT specimens. The theoretical yield strength values for the CFT columns and steel girders were much larger than the experimental shear strengths of the connections. The stiffness of the connections showed good agreement with the calculated values from AIJ-SRC (1997) design provisions in the elastic range. The square interior connection with an outside diaphragm and the square exterior connection that was subjected to variable axial loading exhibited larger decay in stiffness compared to the others. This might be due to possible local yielding and deformation at the connection region. The ratio of the experimental ultimate strength versus the ultimate theoretical strength from AIJ-SRC (1997) for the circular and square specimens excluding the 3D connection ranged between 1.66-1.84 and 1.31-1.62, respectively. Consequently, the effect of confinement should be accounted for in circular connections due to their high experimental over theoretical strength ratios. The strength of the 3D specimen was examined separately for strong axis flexure and about an axis that was 45 degrees to the principal axes of the cross section. It was found to be stronger in the latter direction. All of the specimens exhibited ductile behavior and the rotation capacities ranged from 0.028 to 0.041. For the 3D specimen, the loading direction did not affect its deformation capacity.

References

  • Fujimoto, T., Inai, E., Tokinoya, H., Kai, M., Mori, K., Mori, O., and Nishiyama, I. (2000). “Behavior of Beam-To-Column Connection of CFT Column System Under Seismic Force,” Composite and Hybrid Structures, Proceedings of the Sixth ASCCS International Conference on Steel-Concrete Composite Structures, Xiao, Y. and Mahin, S. A. (eds.), Los Angeles, California, March 22-24, 2000, Association for International Cooperation and Research in Steel-Concrete Composite Structures, Los Angeles, California, pp. 557-564.
  • Nishiyama, I., Fujimoto, T., Fukumoto, T., and Yoshioka, K. (2004). “Inelastic Force-Deformation Response of Joint Shear Panels in Beam-Column Moment Connections to Concrete-Filled Tubes.” Journal of Structural Engineering, 130(2), 244–252. doi:10.1061/(ASCE)0733-9445(2004)130:2(244)