Progressive collapse occurs when damage from a localized first failure spreads in a domino effect manner resulting in a total damage disproportionate to the initial failure. Recent building failures (e.g., World Trade Center twin towers) highlight the catastrophic outcome of progressive collapse. This research proposes a reliable and realistic retrofit technology which installs thin steel panels into steel building structural frames to enhance the system progressive collapse resistance. The steel frames with simple beam-to-column connections, under different boundary conditions (i.e., sidesway uninhibited and sidesway inhibited, respectively), and the loss of one bottom story column were retrofitted using the proposed technology (i.e. installing thin steel panels in the structural frames). Performance of these frames was investigated. Two Finite Element (FE) models which require different modeling efforts were developed to capture the system behavior. The first model explicitly models the infill plates to capture the plate buckling behavior. The second model known as strip model represents the infill panels as diagonal strips. In addition to the FE models, a plastic analysis model derived from the prior research on seismically designed Steel Plate Shear Walls (SPSWs) was considered. The system progressive collapse resistance obtained from the two FE models and the plastic analysis procedure were compared and good agreements were observed. It was observed that installing infill plates to steel structural frames can be an effective approach for enhancing the system progressive collapse resistance. Beyond the strength of the overall system, the Dynamic Increase Factor (DIF) which may be used to amplify the static force on the system to better capture the dynamic nature of progressive collapse demand was evaluated for the retrofitted system. Furthermore, the demands including axial force, shear force and bending moment on individual frame components (i.e., beams and columns) in the retrofitted system were quantified via the nonlinear FE models and a simplified procedure based on free body diagrams (FBDs). Finally, the impact of premature beam-to-column connection failures on the system performance was investigated and it was observed that the retrofitted system is able to provide stable resistance even when connection failures occur in all beams.

Recent research reports that steel Concentrically Braced Frames (CBFs) (even the code-compliant ones) may be susceptible to soft-story failures during strong earthquakes. Such a failure mode causes catastrophic outcomes and should be definitely avoided in practice. This thesis focuses on development and validation of a seismic retrofit strategy for low-rise and mid-rise steel CBFs vulnerable to soft-story failures. The considered retrofit strategy consists of a sufficiently stiff rocking core (RC) pinned to foundation and connected to the existing frame. For demonstration purpose, two representative benchmark steel CBF buildings, which are the three-and six-story CBFs designed forLos Angelesin the SAC Steel Project, are considered. Finite element (FE) models of the benchmark buildings are validated using the published results and explicitly take into account gusset plates, member yielding, brace buckling, brace rupture, and P-Delta effect. Eigenvalue analyses are first conducted to investigate the effect of RC on system modal properties. It is found that the added RC generally does not significantly change the fundamental period and therefore does not attract excessive earthquake force to the system. Additionally, nonlinear static pushover analyses are performed to address the beneficial contribution of RC to the system under the performance objectives including immediate occupancy, life safety, and collapse prevention. The Monte-Carlo simulation technique is used to take into account uncertainty in lateral force distribution and its effect in system seismic performance. It is found that sufficiently stiff RC creates more uniform inter-story distribution along the vertical direction in all considered scenarios. Furthermore, nonlinear dynamic analyses are conducted using three different ground motion suites. It is shown that the systems with properly selected RC can achieve the Best Safety Objective defined in FEMA 356 and ensure the collapse prevention performance under near-fault earthquakes.

published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering

Thesis--M. Sc.(Eng.), University of Hong Kong. / Mimeographed.

Thesis--M. Phil., University of Hong Kong, 1985.

Thesis (M. Sc. (Eng.))--University of Hong kong. / Mimeographed.

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