Moment Connections to Circular Concrete-Filled Steel Tube Columns

As part of the U.S.-Japan Cooperative Research Program on Composite/Hybrid Structures (1992), investigations were carried out at the University of Nebraska-Lincoln and University of Illinois, to develop moment connection details and accompanying design provisions for connecting steel beams to circular concrete filled tube (CFT) columns. This paper provides an overview of the work carried out. Work at the University of Illinois consisted of evaluating the inelastic response of six possible connection details. Six large-scale connections were tested to failure using the quasi-static test method. Connections welded to the skin of the tube created large distortions of the tube wall, and were susceptible to weld, flange, or tube wall fracture. External diaphragm and continuous web details exhibited more favorable inelastic behavior, but the flexural strength of these connections began to deteriorate relatively early in the imposed deformation history. Continuing the flanges through the composite column showed adequate strength, however due to excessive slipping this connection did not dissipate significant inelastic dynamic energy. One of the details tested at the University of Illinois was passing the girder section through the CFT columns. This through beam detail provided the most effective detail to achieve the ideal rigid connection condition. Work at the University of Nebraska-Lincoln concentrated on comprehending the behavior of the through beam connection detail. The behavior of CFT columns under seismic loads was studied through testing six columns which were subjected to a constant axial load in addition to a cyclic lateral load. Failure modes for through beam connection detail were identified through testing seven, two-thirds scale connection specimens. These tests were used to comprehend the force transfer mechanisms between steel beams and CFT columns and develop design provisions that could estimate the capacity of the various elements of the through beam connection detail.