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چكيده انگليسي :

Influence of Foundation Flexibility on Behavior Factor of R C Frame Structures Masoomeh Erfani Jazi m erfanijazi@cv iut ac ir Spring 2009 Department of Civil Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisors Dr A M Halabian mahdi@cc iut ac irdmostofi@cc iut ac irDr D MostofinejadAbstractCurrent force based design procedure adopted by most seismic design codes allows theseismic design of building structures to be based on static or dynamic analyses of elasticmodels of the structure using elastic design spectra The codes anticipate that structures willundergo inelastic deformations under strong seismic events therefore such inelasticbehaviour is usually incorporated into the design by dividing the elastic spectra by a factor R that reduces the spectrum from its original elastic demand level to a design level For astructure supporting on flexible foundation as SSI extends the elastic period and alsoincreases damping of the structure foundation elastic system the structural ductility could beaffected by frequency dependent foundation soil compliances For inelastic systemssupporting on flexible foundations the inelastic spectra ordinates are greater than for elasticsystems when presented in terms of flexible base structure s period This implies that thereduction factors which are currently not affected by SSI effect could be altered therefore the objective of this research is to evaluate the significance of foundation flexibility on forcereduction factors of R C frame structures In this research by developing some generic R Cframe models supporting on flexible foundations effects of stiffness and strength of thestructure on force reduction factors are evaluated for different relative stiffnesses between thestructure and the supporting soil The generic frames are idealized as 2D frames using beamand column elements The non linear behaviour of beam elements is modelled by moment curvature approach while the multi spring model so called as fiber element model isemployed to represent the non linear behaviour of columns Implementing the concept offoundation impedance functions the effect of SSI is taken into account using substructuremethod Using a set of artificial earthquake records repeated linear and non linear analyseswere performed by gradually increasing the intensity of acceleration time histories to a level where first yielding of steel in linear analysis and a level in which collapse of the structure innon linear analysis is observed The difference between inelastic and elastic resistance interms of displacement ductility capacity factors has been quantified The results indicated thatthe foundation flexibility could significantly change the ductility of the system and neglectingthis phenomenon may lead to erroneous conclusions in the prediction of seismic performanceof flexibly supported R C frame structures Key Words Foundation flexibility R C frame structure Behavior factor Dynamic analysis

عرفاني جزي، معصومه

بررسي اثر انعطاف پذيري فونداسيون بر ضريب رفتار سازه هاي قابي بتن آرمه

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