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(詳細はstructures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers, the need of seismic retrofitting is well acknowledged. Prior to the introduction of modern seismic codes in the late 1960s for developed countries (US, Japan etc.) and late 1970s for many other parts of the world (Turkey, China etc.),〔(NZSEE Bulletin 39(2)-June 2006 )〕 many structures were designed without adequate detailing and reinforcement for seismic protection. In view of the imminent problem, various research work has been carried out. State-of-the-art technical guidelines for seismic assessment, retrofit and rehabilitation have been published around the world - such as the ASCE-SEI 41〔(ASCE-SEI 41 )〕 and the New Zealand Society for Earthquake Engineering (NZSEE)'s guidelines.〔(NZSEE 2006 )〕 These codes must be regularly updated; the 1994 Northridge earthquake brought to light the brittleness of welded steel frames, for example. The retrofit techniques outlined here are also applicable for other natural hazards such as tropical cyclones, tornadoes, and severe winds from thunderstorms. Whilst current practice of seismic retrofitting is predominantly concerned with structural improvements to reduce the seismic hazard of using the structures, it is similarly essential to reduce the hazards and losses from non-structural elements. It is also important to keep in mind that there is no such thing as an earthquake-proof structure, although seismic performance can be greatly enhanced through proper initial design or subsequent modifications. ==Strategies== Seismic retrofit (or rehabilitation) strategies have been developed in the past few decades following the introduction of new seismic provisions and the availability of advanced materials (e.g. fiber-reinforced polymers (FRP), fiber reinforced concrete and high strength steel).〔( Moehle, J. (2000) State of Research on Seismic Retrofit )〕 Retrofit strategies are different from retrofit techniques, where the former is the basic approach to achieve an overall retrofit performance objective, such as increasing strength, increasing deformability, reducing deformation demands while the latter is the technical methods to achieve that strategy, for example FRP jacketing. *Increasing the global capacity (strengthening). This is typically done by the addition of cross braces or new structural walls. *Reduction of the seismic demand by means of supplementary damping and/or use of base isolation systems.〔(Filiatrault & Cherry (1986) )〕 *Increasing the local capacity of structural elements. This strategy recognises the inherent capacity within the existing structures, and therefore adopt a more cost-effective approach to selectively upgrade local capacity (deformation/ductility, strength or stiffness) of individual structural components. *Selective weakening retrofit. This is a counter intuitive strategy to change the inelastic mechanism of the structure, while recognising the inherent capacity of the structure.〔(e.g. Kam & Pampanin (2008)- Selective weakening retrofit for RC frames )〕 *Allowing sliding connections such as passageway bridges to accommodate additional movement between seismically independent structures. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Seismic retrofit」の詳細全文を読む スポンサード リンク
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