Self-centering post-tensioned energy dissipating (PTED) steel frames for seismic regions

This doctoral dissertation is aimed at contributing to the development of post-tensioned steel structures by proposing a moment-resisting connection that incorporates high strength post-tensioned steel elements along with energy dissipating bars. The most significant characteristic of these Post-Tensioned Energy Dissipating (PTED) connections is their capacity to ensure small residual drifts through self-centering properties, even when significant inelastic transient deformations are mobilized during cyclic loading. In addition, these connections can be designed to provide the desired amount of energy dissipation.; Experimental investigations on energy dissipation bars, a large-scale test on an exterior connection and a 0.45-scale test on a frame assembly were carried out to validate the PTED concept, and to demonstrate that these connections were capable of achieving stiffness and strength characteristics comparable to traditional welded moment-resisting connections. A series of numerical models, including an iterative sectional analysis procedure, a nonlinear rotational spring model and an axial spring model accounting for the beam depth were proposed. These models were validated against experimental results.; The dynamics of single-degree-of-freedom (SDOF) systems exhibiting the flag shaped hysteresis characterizing PTED connections was investigated by studying the frequency response under sinusoidal excitation. Results from nonlinear time-history dynamic analyses on hysteretic self-centering SDOF systems indicated that the seismic response of these systems can be similar to the response of elastoplastic hysteretic systems. Based on results from these nonlinear time-history analyses, a design procedure for PTED frames was proposed. Numerical analyses on MDOF frames first designed as welded moment resisting frames and then as PTED frames following the proposed design procedure indicated that, under code level seismic loading, the maximum interstory drifts and maximum accelerations of these two types of systems are very similar. However, unlike the welded frames which sustained considerable residual drifts along their height, the PTED frames sustained only limited residual drifts in the first story. The work presented in this dissertation suggests that the proposed PTED connections offer a viable alternative to welded moment resisting frames in seismic regions.