بررسي تاثير زبري هاي موضعي در كنترل و كاهش آب شكستگي موضعي تكيه گاه پل

چكيده انگليسي :

129 The Effect of Local Roughneses on Reduction of Local Scouring at Bridge Abutment Hamed Shahsavari hshahsavary@yahoo com September 20 2015 Department of Water Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Manouchehr Heidarpuor heidar@cc iut ac irAbstractBridges are one of the most important structures which are under attention from many years ago Bridgeis a structure to cross over obstacles such as rivers or valleys In recent decades despite using modernmaterials and technology and spending a lot of costs for designing and building bridges failure of them iscommonly reported due to flood and local scouring Local scouring occurs by placing obstacles such asabutments in flow direction Increasing the resistance of bed materials and decreasing the power oferosion factors are the ways to stand against local scouring To decrease the power of erosion factors horseshoe and wake vortex equipment such as collars submerged vanes and etc are being used One ofthe ways of controlling and reducing local scouring is to create roughness on abutments which areprominences that made while concreting spherical and angled rings In this study by creating roughnesson semi circular abutment their effects on reducing scour depth are investigated and also flow structure isbeing compared around simple abutment and abutment with roughness Experiments were conducted in atransparent rectangular Plexiglas flume with length of 7 m width of 0 32 m depth of 0 35 m anddischarge of 10 5 liters per second The experiments were dune under clear water scouring and with bedmaterials sizing 0 75 mm The 3 D instantaneous flow velocity in different cross sections was measuredusing an Acoustic Doppler Velocimeter ADV Results revealed that the best condition of placingroughness with descriptions of depth of roughness c 0 1L roughness intervals b 0 45L and withconstant height of a 0 05L the roughness has reduced the intensity of scouring and decreased the finalscour depth by 47 L is the length of abutment Also by increasing roughness intervals scour depth isreduced and this reduction continues till a specific value and after that the efficiency of roughness wasreduced It means that there is an optimum value for placing roughness on abutment to reach the bestperformance By doing experiments and finding the optimum value of roughness intervals the bigger thesize of roughness the more performance they have Also velocity profiles shear stress and turbulencewere investigated and quadrant analyses were done to study flow structure Results of shear and velocityprofiles around abutment reveal the existence of downward flow and horseshoe vortex in upstream anddownstream profiles show wake vortex and turbulence behind the abutment But the main result of thisstudy is the effect of roughness on flow structure around the abutment which reduces the power ofscouring elements Also quadrant analysis shows that the most common phenomenon around theabutment and near bed is sweep and ejection Keywords Abutment Local scour Local roughness Flow pattern Quadrant analysis

شهسواري، حامد

بررسي تاثير زبري هاي موضعي در كنترل و كاهش آب شكستگي موضعي تكيه گاه پل

الگوي جريان , آناليز كوادرانت