The ob ] ective of this paper is to develop a mechanical model fbr direct shear failure ofconcrete , focuslng on the entare load −displacement charactenstics The method rnakes use of totated smear ¢ d crack model , truss model theory and mterlockmg shear transfer model , combmed m a simple model . The analysis emp ] oys the development of multiple diagonal cracks under far field . uniferrn shear stress and macroscoplc sheaT cTack propagation The modehs venfied through the companson ofthe model

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... spredietion with both expenmental measurementS and nonlmear Finite Element Method ( FEM ) analysis results The mOdel is found in good agreement wtth both expenmentS and FEM analysis , indicating tha" t can be used as a reliable tool f ( )r reasonable first es " mate fi ) r Mechamsm of shear behav 且 or has been su 切ected to heated debates In past decades . However , It has not been clarified sufficlently yet, Mechanlsm ofnonlmear behavlor m concretc stmct 凹rcs mainly depends on crackmg phenomena associated wlth straln softening , ・ Therefbre, it ls necessary to exa 皿 me straln softenlng behavlor of shear fractUre process m order te make clear the nonhnear mechamsm The amount of experimental data on the mechamcal propert1es of shear fracture process zonc Is too hmlted For making clear the shear transfer mechamsm and stram sof亡 enmg behavior ofthe 丘acture process zone , shear tests were perf { )rmed by Ish 且 hara and Mlhashi " , In the t¢ st, 重 t was found that approximately four stages of shear fracIure mechanlsm were observed ( see Flg. 1 ) . The first was the stage befbre crack Imt 且 atlon 〔 1) , the ' ロ ' second was the stage of crack propagation( H) , the third was a transltien stage after crack propagatlon ended ( III ) , and the final stage was a stable aggregate interlocking stage ( IV) . Based on the ground ofthe aforemcntiened stUdy , the present work aLms at developlng a simple mechanicat model fbr山 e analys 置 sofenhre load− displacement characterlstics ofshear 伽 lure ofconcrete under dlrect shear loadmg 、 The mtent ofthls modeling methodology lsbased on the fact that 且 hs often posslble to find general analytlcal solutions , which are much cas 置 er to hafidle than complek nunierical solutlons such as nonlinear FEM analysis The propQsed model ls fbmulated by modify 且 ng the onginal mode1 , whlch was developed to predlct the ennre shear stress − d且splacem 巳nt characterlstics 董 br shear keys , deep beams and membrane elements zb l) ・ 4 レ Spec且fically , the present model employs the lnterlockLng model and can account fbr the transrtlon stage ( HI ) and the interlocking slage ( 畳 V )whlch were not considered in the ongmal modeL 2. NUMERICAL FORMULATION OF MECHANICAL MODEL 「 2. 1Frac 重 ure Sequence otShear Fai置ure Based en the experiment by ishlhara and Mihashi n shown in Flg. 2, the following simple f 由 cture sequence of shear failure Is macroscopica ] ] y constructed and isschematically shown m F 聖 g 3 Phase I A1 the first stage of loading , flaws near thejoint ar ¢ easlly actlvated by tensl 且 e stress mduced due to shear stress . Then, intens 且 ve multlple crackingoccurs on the local prmcipal stress trajectones , and fbmms ashear fractured zQne roughly ahgned ( mode hmtlatlon ) The multiple cracks a 爬 assumed evenly dLst ロ buted along the shear fをactured zone wlth a certainang 且 e ofmclinatien Although m reality such distributaen is not umfbrm , th正 s slmplification co 山 Id be supPorted by the ' cnncal zone ' concept along the direct shear plane ' ) ' w 且 thm a cracked reg 且on , the extenslve