Design, analysis, and experimental behavior of seismic resistant post-tensioned steel moment resisting frames

A post-tensioned (PT) connection for steel moment resisting frames (MRFs) was developed. The connection requires no field welding, and returns the structure to its pre-earthquake position (i.e., exhibits a self-centering capability). Bolted top and seat angles are used in the connection, along with PT high strength strands that run parallel to the beam. The strands compress the beam flanges against the column flange to develop a resisting moment, while the two angles and the friction between the beam and column resist shear. Under the bending moment from strong earthquake loading, a gap develops at the interface of the beam tension flange and column flange as the beam tension flange separates from the column flange. The angle attached to the beam tension flange subsequently yields and dissipates energy under cyclic loading. As the bending moment returns to zero, the gap closes resulting in no permanent deformation of the connection.; The scope of this study included full-scale experimentation, the development of a design procedure, and analytical studies of frames with PT connections. Full-scale interior PT connection subassembly specimens were subjected to severe inelastic cyclic loading. Design criteria and a design procedure for steel frames using PT connections were developed based on a performance-based design approach. Using nonlinear dynamic time history analyses, the seismic behavior of several 6-story, 4-bay PT MRFs with different design parameters was examined to evaluate the effects of these design parameters on the seismic response. The performance of the PT MRFs was compared to the performance of a MRF with welded connections.; The results of the investigations demonstrate that a PT connection performs well under large cyclic inelastic story drifts, and that this new concept offers a viable alternative to welded or bolted moment connections for seismic resistant design. The beams and columns remain elastic while only the top and seat angles behave inelastically and dissipate energy. Frames with PT connections have good energy dissipation and ductility, while maintaining a self-centering ability. During the design level earthquake, the story drifts of MRFs with PT connections are generally comparable to that of MRFs with welded connections. Based on the analytical results, the extent of structural damage in a PT MRF after an earthquake is expected to be less than that in a MRF with welded connections.