COMPARISON OF PSEUDO-STATIC AND DYNAMIC RESPONSE ANALYSIS OF SIBILU DAJ\'I

Abstract

Dynamic loads induced by earthquakes arc often major factors in the design of earth dams . Earthquake induced stresses arc major factors in determining the angles of the dam slopes and significantly influence the selection of materials. the zoning of the dam, and the construction method. Awareness about more rigorous seismic stability analysis is also growing during recent years . . , • . In Ethiopia dams a.�;be'ing constructed for various purposes . The analysis and design of ,, ,I·; dams has been carried out by taking many factors in to account . Among these factors earthquake effect is considered mainly for major dams . One of these dams is the Sibilu Dam. which is under design for the Addis Ababa water supply. Until the present, in Ethiopia. seismic effect is couunonly considered by the pseudo-static analysis method. But representation of the co mplex. t ra n s i en t an d d yn a m ic effects of earth q uake sha k ing , . , . by constant ps e udo-static force s is obviously not accu ra te . I n this thesis an attempt was made to com pa re t he p s eu d o -s tati c a nd dyn ami c r es po ns e ana l ysi s by t ak in g the Sibilu Dam as a case s tu dy . The m ain purp os e o f the stud y i s to sho w the shortcomings or ' the pseudo - static an a ly sis m ethod as co mpared to th e dvnarnic response analysis when applie_ d to the analysis o f earth/ rock ti ll dam s. The thesis i s orga n iz ed as fo llo w s : initially a back g round is gi v en on seismici ty and seisrmc haza r ds in g eneral and Ethio p i a in p a rt icul ar The second chapter covers summar y of pre v i o us wor ks r e lat ed t o this stu dy . 111 th e thi r d ch a pter some descrip t ion is g iven a b o ut the Sib i lu D a m, the da m under the case stud y . l n chapter four, the de fi nition of the e x pected s e ism i c e x cit a tio n for th e dam s it e i s p re s e nte d . The hi s torical records of earth q ua ke e v ent s arc coll e cted a nd g cot c chnical data o f th e dam site · are reviewed - , _. l"I paying special attellfs9n to the location of active faults. The obtained data set is analyzed . _ .. · to give the required earthquake parameter for two different return periods. i: . In fifth chapter, the pseudo-static slope stability analysis is done with the conventional limit equilibrium method by using the design ground motion as an input . The analysis is performed for the upstream and down stream slopes of the dam by varying the possible critical cases. In chapter six. analysis and design is done based on permissible deformation. The dynamic response analysis is done by varying the material behavior. Non-linearity is considered by the Equivalent Linear Method. Finally, comparison of the different analysis methods is made and conclusions and recommendations are drawn.