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چكيده انگليسي :

Experimental Study of Local Scour at Bridge Pier with Raft Footing Mohammad Javad Aarabi mjaarabi@cv iut ac ir Date of Submission October 01 2011 Civil Engineering Department Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisors Dr Mohammad Reza Chamani mchamani@cc iut ac ir Dr Keyvan Asghari kasghari@cc iut ac ir AbstractScouring in the river is a phenomena which is the result of interaction of flowing water and sediments whichchanges the topology of the rivers bed and coastal area The most common cause for bridge failures reported inthe literatures was due to pier scour Three dimensional flow filed with sediment transport and mobile channelbed during scour process leads to a complex problem It is known that pier scour can be studied in either clear water or live bed conditions Most of studies in this topic were carried out empirically During past decades several methods were used to control and reduce the scour depth In addition to structural and geotechnicalcountermeasures footing may reduce the scour depth around bridge piers Raft footings are commonly used inhistorical bridge e g Sie o Se Pol Bridge in Isfahan city in Iran which was built in 1602 It can be also used forlow span bridges where continuous footing are necessary In this study the effect of raft footing on local scour at bridge pier was investigated based on model study underclear water condition Experiments were carried out in the Hydraulics Laboratory of the Civil EngineeringDepartment at Isfahan University of Technology Experiments were performed in a 9 m long 0 40 m wide and0 70 m height flume The 40 mm diameter cylindrical pier was made of Teflon The bed material was uniformsand with median diameter of 0 72 mm and standard deviation of 1 26 Width of raft footing was chosen as oneto four times of pier diameter The top elevation of the raft footing was set at the elevation of bed The dischargewas fixed at 26 1 L s The experiments were performed to attain the equilibrium scour depth based on Melvilleand Chiew 1999 criteria The topographical mapping at the equilibrium depth are obtained for additionalcomparisons between the cases of piers with and without raft footing It is shown that raft footing alleviate the scour depth It is shown that scour depth upstream of the raft footingwith width equal to pier diameter reduced 52 percent as compared to the scour depth at bridge pier withoutfooting With width of raft footing reaches two times or more of pier width no scour hole developed upstreamof the raft footing Raft footing also leads to reduced scour depth downstream of the pier Using raft footing thetime of the equilibrium scour depth was increased as compared to the scour depth at bridge pier without footing In the case of raft footing with width of pier the equilibrium time increased 71 percent of the time needed forthe equilibrium of scour depth at bridge pier without footing Scouring downstream of the raft footing createdtwo scour holes at a specific distance from the raft footing With increasing the width of the raft footing thelocation of the equilibrium scour depth downstream of the raft footing migrated to the centerline of the flume Similar results were seen in previous studies with bed sill located downstream of the pier Key WordsLocal scour Bridge pier Raft footing Clear water

اعرابي، محمدجواد

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