The final collapse of building structures under severe earthquake excitation will undergo stiffness degradation, which may be revealed by continuously monitoring and investigating the response of the specified component. Based on the on-line parameter-estimation feature of model-reference adaptive structural control algorithm, a real-time model-reference adaptive identification technique (MRAIT) is proposed in this study. The adaptation law for parameter estimation is designed based on Lyapunov's direct method. An energy-like candidate function is defined by composing of weighted response-tracking error and weighted parameter-estimation error. An artificial adaptive signal is calculated from both the simulated states of predesigned model and the adjustable parameters estimated by MRAIT. With the help of the proposed MRAIT under some minor earthquakes, the time-invariant dynamic properties of target structure can be identified step by step by modifying the predesigned model according to the estimated adjustable parameters. The onset of yielding or the degradation on stiffness of an elastoplastic model can be revealed if the proposed MRAIT is equipped and monitored continuously when subjected to severe earthquakes. The failure patterns of hysteretic-type structures undergoing inelastic behavior can be recognized either by the monitored artificial adaptive signal or by the variation of tracking error calculated on-line. Therefore, the onset of damage can be assessed based the proposed real-time MRAIT scheme. Copyright © 2009 John Wiley & Sons, Ltd.

Current studies lack probabilistic evaluations on the performance of fault-crossing bridges. This paper conducts seismic fragility analyses to evaluate the fragility of cable-stayed bridges with the effects of fault ruptures. Synthetic across-fault ground motions are generated using existing simulation methods for the low-frequency pulses and high-frequency residuals. Incremental dynamic analysis is utilized to generate the seismic responses of the bridge. The optimal intensity measure (IM) for a cable-stayed bridge that crosses a fault is identified based on the coefficient of determination (R²). Root-mean-square velocity (V_rms) is found to be the best IM for cable-stayed bridges traversed by fault ruptures, instead of the commonly used ones such as peak ground acceleration or velocity (PGA or PGV). Fragility curves for the critical components of fault-crossing cable-stayed bridges, including pylons, cables, and bearings, are developed using the IM of V_rms, and are subsequently compared with those for the cable-stayed bridge near faults. Results show that the bearings on transition piers are the most vulnerable component for fault-crossing cable-stayed bridges because of the rotation of their girder. Compared to cable-stayed bridges near faults, pylons and bearings are more vulnerable in the transverse direction for cable-stayed bridges crossing faults, whereas the vulnerability of cables is comparable.

In situ push-over experiments and analytical assessments were conducted in this study to investigate the seismic capacity of RC school buildings at the Guan-miao Elementary School in Tainan City, Taiwan. Both prototype and external steel-framing specimens were constructed and compared. Reinforcements with steel channels were adhered to the captive columns and their adjacent beams in the weak direction, to retrofit the school building through the creation of external steel-framing systems. The design and construction procedures of the beam-column connection are introduced, as well as detailed drawings of the column-base anchorage system, both of which are key to the effects of the proposed retrofitting method. The experimental results show that the steel-framing system can be firmly bonded to the retrofitted specimen, providing continuous stress transference from the beam-column joints to the steel channels. The failure mode of the retrofitted captive columns was shifted from shear failure, as seen with the prototype specimen, to flexural-shear failure, with the retrofitted one. Both the experimental and analytical results show the following: The maximum total base shear strength increases 2.11 times, the total enclosed area of the stored energy increases 2.20 times, and ductility capacity increases 1.31 times. The external steel-framing systems proposed in this work can thus effectively enhance the base shear strength and the ductility of the specimens.