In current seismic dosign praσ tice , dle design yield streng 血 of a str 巳 oture is typiGally Qbta孟 ned through thc use of strengh reduotien factor that reduces elastic stre皿 g 山 demand to design levels , Tlie streng 血 reductien ictor due to 丗 e 血elastio behayier of struc呱 e is usually 鉛 mula 脆 d 血 t s of 剛 um duc 晦 血 s conv ti 。nal appreach fails to 。onsider cumulative darnage that 。ccurs under eyclic loading. h1 this stud } -damage ・ based strength reducdon factOr was evaluated 丘om the streng

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... 由 dcmands computed oonsidering cun1Ulative darnage and different site conditions , The results indicate that the spectral shape of darnage・ based streng 宜 h redu ion factor has similarity with tlle conventional ductility − based reduCtion faCter . A 皿 equivalenUimit duotility ratio as a certain percentage ofthe monotonic ductility capacity may therefbre also be used . This reductiQn depends on the monotollic ducti1 正 ty capacity and while it is not significantly afirected by the natural period ofthe structu τe, it shou 蓋 d be carefし dly evaluated in亡 he case of so 丘 soil site and where the natUral period ofthe stUctUre is close to the predominant pedod ofground motion . Simple expressiens for estlmating thc darnage・ based strength reduCtion factor are also proposed, K の ywOttls : stiength denumd, , seismic design strength redUctionfactor , ductility demand, itysteretic energy , α ρ嬲 如 ' 漉 面 η θ, site COtidition 1. Introduction Structures are usua1ly designcd wi 血 1飢 er飢 strength lower than that required fbr it to respond elastioally in血e event of a severe earthqu 乏止e . The design yield strength can be obtajned by applying response modific 題tion factor or s ngth redu σ口 on factor to reduce elastic streng 血 demand to design lcvel , This factor which varies in different oountries ( ノ -一 飽ctor in thc US seismic code er its equivalent q ・ f註 ctor in the Eurocode , or its reoiprooal , the stmc 漁 1 coef 髄cient D 、 of Japan )may consist of faCtors related to the inelas 廿o bohavior ofthc stm 伽 fe, overstrength . and redundancy . Most ef existing stUdies on the strength reducdon factor related to 廿1e inelastic behavior haye been formulated in terms of limiting the rnaXimum ductility . A comprehensive review ean be found in the work ofMjranda and BerteroD, where strength reduction factors based on maXimum ductility demand preposed by several s加 dies are compared . However , a shorbcoming of this conve 面 onal apProa σh 重 s dlat i亡 aims to con 血ol 血e maxjm deformation but not 血 e cumulative darnage under repeated load reversals . Tc ) illustrate this poin ち the time history response of a single − degree ・ of 一 廿eedom syst with a n 1 pe πiod of O. 5 s and a lateral yield s鵬 ngth equal to O , 190f its weight when s ゆjected to l940 EI C 血 o NS ground motion is shown in Fig. 1 − a . It can be seen that the maximum deformation is 3 、 8t es of the yield deformation ql , . When the yery same s恤 。t購 is su 切 eoted to l989 Foster City OOO ground motion , it can be seen f } om Fig, 1・ b that the maximum response is also 3 . 8A , occurr g in the opposite direction 、 Howeveら When the amounts of hysteretic energy dissipated are examined , it oan be seen that 山 ere is a big difference between these two cases . For the El Centro NS , the dissipated hysteretic errergy Eh is 25 , 8 妬 処 whereas that of Foster OOO is only about half ( 14. 5MyA ) . This is because 血e latter is characterized by small load reversals Within the hysteretic envelope wherc thcre is no hysteretic energy dissipated ( see Figs. 1 ・ b and 2− b ) . These tWo cases ebviously result to different 且 evels ofseismic damage , It is evident 食om the above examp 監 e that tlle limitation of maximurn duCtility suggested by the conventional strength reduction factor is insufficiertt in controll 血 9 cumula 口ve damage to 山 e structure . 皿 rere also exists a study on streng 血 reduCtien f r based oll seismic da皿 age2 〕 . However the hysteretie model used is the elastOplastic model without streng 山 and stiMless degradation known to have significant 血fiuence on 重 11e behavief ef st口』ctUres , The effect of sofi soi】condition was also not considered , The ebjective ofthis study is to detem 血 e streng 血 demandS日nd strength reduction fbctor tak 血 g into account curnUlative damage while consider 血 9 strerlg血 and stifihess degradation as well as different site conditiens , Factors affeCting damage − based strength reduCtion fbOtor are also exam 血cd and regressien analysis performed to obta simpIe eXPressions ft ) r est at血 9 damage − based streng 血 reducHon faCt ' )r. や 1Graduate Student, Grad . School of Engineeriug,