Study On The Design Method Of Passive Controlled Structures Based On Collapse Modes

Earthquakes caused significant damages on structures which are deemedresponsible on serious human casualties. Current seismic design code stipulates thestrength and stiffness distribution along the height in order to realize an ideal damagemode. The reality, however, shows big deviation from the design concept sincestory-deformation concentrated collapse modes were still common as observed in recentearthquakes. Recent study indicates that the passive control technique is one of the mostappealing approaches to improve the seismic performance of structures. This study firstexamines one of the popular design methods used for structural enhancement usingpassive dampers. Then a new damper is designed and examined physically. Finally animproved method to control the collapse mode is proposed. Major findings aresummarized as follows:(1) The passive design method developed in Japan is examined numerically using afirst-story weak steel moment frame. The performance design curves are plottedaccordingly. In order to examine the seismic performance of the retrofitted structure,finite element model is employed. Time history analyses indicate that the retrofittedstructure performs well under the design earthquake, but story concentration occurs ifthe earthquake is larger than the level considered during design stage. This proves thecurrent design method cannot control the collapse mode effectively.(2) A metallic damper is developed which is featured with slits, or called slit-walldamper. The slit-wall damper has a more stable behavior and larger energy-dissipationcapacity than the one without slits. Moreover, the slit pattern renders it a flexibility todesign the strength and stiffness separately, making the design more versatile and easier.(3) An improved design method is developed in this study. The second stiffnessafter yield is explicitly considered and incorporated into the design procedure to controlthe collapse mode. It is found that the second stiffness ratio of0.5is able to achieve themost uniformly distributed deformation along the height. A steel moment frame isdesigned and analyzed numerically to demonstrate the effectiveness of the improveddesign method. A substructure specimen is also prepared accordingly.