اثر پره هاي مستغرق بر روي آبشستگي گروه پايه

چكيده انگليسي :

Effect of Submerged Vanes on Local Scouring at Bridge Piers Group Zahra Eshaghy Eshaghy zahra@yahoo com 19 12 2012 Department of Water Engineering Collage of Agriculture Isfahan University of Technology Isfahan Iran Language FarsiDegree M ScManouchehr Heidarpour heidar@cc iut ac irHossein afzalimehr hafzali@cc iut ac irAbstractScouring is a phenomenon that causes bridge collapse Several studies show that 60 percent of bridgescollapse is related to scouring Different methods have been suggested to protect and reduce scouringaround bridge piers Some of them are using riprap collar slot and etc Using of vane was suggested as amethod to reduce local scouring around bridge piers Scouring around single pier had been thoroughlyinvestigated in past however there are not many investigations regarding scouring at pier groups Sincescouring around piers group is affected by factors which are not in determinant single pier therefore survey of them is necessary Important effects in scouring pier groups are reinforcing sheltering horse shoe vortex compression and shed vortices In this study effect of space between piers on scouring andthe vanes efficiency on pier groups were investigated Experiments were carried out under clear waterscour conditions with constant discharge in horizontal re circulatig flume in Hydraulic Laboratory at theIsfahan University of Technology in Iran for a period of approximately 8 h after which an equilibriumstate of scour was achieved The flume had 7 m long 0 32 m wide and 0 35 m deep Uniformly gradedsand with median diameter d50 of 0 71 mm and geometric standard deviation 1 26 was applied Thediameter of the piers was 20 mm and the distance between the piers center to center were 2 3 4 and 5times b b is the pier diameter The vane had 2cm long 10 mm thickness and 13 cm height and vaneangle was 18 5 laboratory flume experimental detection were made by using ADV to determinevelocity Reynolds stress distribution and turbulent intensities Scour hole was frozen by cement tofacilitate performance of the experiments The results of the experiments showed that the vane causedincreasing of the sheltering effects Vane effect on reduction of scour depth was negative on first pier inpier groups The vane caused that effect of reinforcing decreased with increasing number piers from 2 to3 and scour depth of first and second piers were increased Efficiency vane was 27 and 12 3 percent respectively at spaces 2b and 3b in second pier of two pier groups Efficiency vane in meddle pier of threepier groups was 41 8 and 32 7 percent and in rear pier was 28 5 and 18 18 percent respectively at spaces2b and 3b The vane had negative effect at two and three pier groups with spaces 4b and 5b In upstream the velocity profiles and turbulent intensities showed that the existence of primary vortex associated withdown flow Within scour hole and in downstream wake vortex caused irregularities in flow pattern Thevane caused increasing down flow velocity at front of first pier The RMS and velocity profiles showedthat oscillations of velocity in downstream piers caused the velocity reduced in this region and wakevortex was the main factor for oscillations of velocity Magnitudes turbulence intensities increased withenter to scour hole and within the scour hole there was a core of higher magnitude of turbulenceintensities at front of the pier as a result of the flow separation which occur at the front of the pier Key words Scour Bridge piers Pier groups Vane Acoustic Doppler velocity ADV

اسحقي، زهرا

اثر پره هاي مستغرق بر روي آبشستگي گروه پايه

پايه هاي پل , دستگاه سرعت سنج صوتي