Kingsley et al. 2005
This research investigates the performance and constructability of embedded-type CFT column-concrete footing connection with slender tubes of high-performance vanadium-alloy steel. A parametric study was conducted to determine the influence of the primary connection parameters and the test variables.
Experimental Study, Results, and Discussion
Three columns were constructed and tested to determine the influence of the embedment depth and vertical reinforcement in the footing. The connection tested consisted of an annular ring welded to the base of the circular section tube and embedded directly into the foundation. A specialized construction method was used in which a slender (D/t = 80) spiral welded tube manufactured using a high-strength, vanadium-alloy steel was used and filled with a low shrinkage, self-consolidating, high-strength concrete. The steel tubes were 20 in. in diameter and 0.25 in. thick.
Two columns with embedment depths of 0.6D and one column with embedment depth of 0.9D were tested. One specimen with the 0.6D depth had vertical reinforcing in the footing, the other did not. Specimens were placed under vertical compression and then underwent cyclic lateral loading. The drift history was based on ATC-24 protocol.
Tests showed that the presence of vertical reinforcement in the footing improved the symmetry of the hysteretic response and permitted tube yielding to occur. However, the specimen with vertical reinforcement was not much stronger than the one without and ductility and inelastic deformation capacity were largely unaffected. In the 0.6D specimens, footing damage was extensive and this contributed to failure of the specimen. Major footing damage occurred at about 2% drift ratio. In the 0.9D specimen, failure resulted from buckling and subsequent tearing of the steel tube. Tube tearing initiated at 6% drift ratio and grew to nearly complete tearing around the perimeter of the tube at 8% drift ratio.
Each of the specimens was able to achieve the nominal moment capacity of the column (determined using the strain compatibility method), despite exceeding the AISC D/t ratio limit. Each specimen exhibited an initial stiffness similar to the AISC design column stiffness, indicating that the connection did not contribute flexibility to the system at low drift levels. The authors conclude that the test results indicate that the proposed annular-ring embedded connection was effective and practical.
Reference
Kingsley, A., Williams, T., Lehman, D., and Roeder, C. (2005a). "Experimental Investigation of Column-to-Footing Connections for High-Strength Vanadium Steel Concrete Filled Tube Construction," International Journal of Steel Structures, 5, 377-387. Kingsley, A. M. (2005b). “Experimental and Analytical Investigation of Embedded Column Base Connections for Concrete Filled High Strength Steel Tubes.” M.S., University of Washington. Kingsley, A. M., Lehman, D., and Roeder, C. W. (2006a). “Experimental and analytical investigation of vanadium micro-alloyed concrete-filled tube-concrete footing connections.” Stessa 2006: Proceeding of the Fifth International Conference on Behaviour of Steel Structures in Seismic Areas, Yokohama, Japan. Kingsley, A. M., Lehman, D., and Roeder, C. W. (2006b). “Seismic performance of high strength vanadium alloy concrete filled tube column-footing connections.” Stessa 2006: Proceeding of the Fifth International Conference on Behaviour of Steel Structures in Seismic Areas, Yokohama, Japan. Kingsley, A. M., Williams, T. S., Lehman, D. L., and Roeder, C.W. (2006c). “Experimental and Analytical Investigation of Vanadium Micro-Alloyed Concrete-Filled Tube-Concrete Footing Connections,” Tubular Structures XI, Proceedings of the Eleventh International Symposium and IIW International Conference on Tubular Structures, Packer, J. A. and Willibald, S. (eds.), Québec City, Canada, 31 August-2 September 2006, Taylor & Francis, Leiden, The Netherlands, pp. 487-494.