Seismic resistant connections for concrete filled tube column-to-wide flange beam moment resisting frames

A research program was conducted to study the seismic behavior of concrete filled tube (CFT) column-to-wide flange (WF) steel beam moment connection in moment resisting frames (MRFs). The research reported herein focuses on the effect that various connection details have on the strength, stiffness, ductility, and force transfer mechanism in these types of connections. The study was conducted in conjunction with the U.S.-Japan Cooperative Earthquake Engineering Research Program Phase IV on Composite and Hybrid Structures.; Both experimental and analytical studies were conducted. The experimental studies consisted of inelastic cyclic tests of large-scale cruciform specimens. A total of 10 large-scale experimental specimens were tested. The connections investigated in this program included: interior diaphragm connections, extended-tee connections, split-tee connections, and post-tensioned connections. The analytical studies included nonlinear finite element analysis of split-tee connection details subjected to axial gravity load and lateral load. A cost analysis of these connection details was conducted to evaluate the relative cost of these connections, which included material, shop, and field cost.; The results of the experimental study demonstrated that extended-tee as well as split-tee connections provide exceptional cyclic joint stiffness and strength for a weak beam-strong column MRF system with CFT columns, and therefore provide a viable alternative to connections with diaphragms for seismic design. The presence of shear tabs in the split-tee connections had only a minor effect on overall behavior. The split-tee connection having snug-tighten tension bolts was found to perform comparable to the connection with fully-tighten tension bolts. The low cycle fatigue effect however should be considered for these bolts under seismic loading. The post-tensioned connections can provide strength and ductility for a moment resisting frame subjected to inelastic cyclic loading conditions. The post-tensioning force provides both moment capacity and self-centering capacity. Yielding in the beams must be minimized by adding shim and reinforcing plates in order to maintain the stiffness, strength, and self-centering capacity of the connection. Design equations for post-tensioning connection for predicting connection response are presented and found to correlate well with the test results.; The finite element analysis study of the welded split-tee connections indicated that the thickness of the split-tee flanges and the pre-tensioned through column bolts must be properly designed to prevent prying action in the bolts. Higher pre-tensioning bolt forces in the through-column tension bolts and a smaller width-to-thickness (b/t) ratio of the steel tube resulted in a higher principal stress in the concrete compression strut in the CFT column panel zone. The setback length of the tee stem has a significant effect on the strength of the split-tee connection. To minimize the reduction in connection strength it is recommended to keep the g/t ratio less than 2.5. Simple equations are developed to predict the strength of a split-tee connection. The shear tabs in a split-tee connection can be omitted if the tee stems and column tension bolts are designed to resist the vertical shear force developed in the beam.