تاریخ دریافت: 29 مرداد 1395،
تاریخ بازنگری: 26 اردیبهشت 1396،
تاریخ پذیرش: 29 فروردین 1396
چکیده
ادارۀ فدرال بزرگراههای آمریکا در بررسی آمار شکست پلها به این نتیجه رسیده است که دلیل اصلی شکست آنها آبشستگی موضعی اطراف تکیهگاههای جانبی، در مقایسه با آبشستگی پایههای پل، است.. روشهایی مختلف برای کاهش آبشستگی موضعیدر اطراف پایههاوتکیهگاههایجانبیپلپیشنهاد شده که یکی از آنها استفاده از پرههای مستغرق است. در پژوهش حاضر به بررسی عملکرد استقرار پرههای مستغرق در کاهش آبشستگی موضعی تکیهگاه پل با دماغۀ گرد بهصورت آزمایشگاهی پرداخته شده است. آزمایشها در یک فلوم با مقطع مرکب و با استفاده از رسوبات غیرچسبنده با قطر متوسط 1 میلیمتر و در دو مرحله اجرا شدند: بدون حضور پرههای مستغرق و با حضور پرههای مستغرق. پرهها با طول 10 و ارتفاع 33/3 سانتیمتر (3L/H=)، در پنج نوع آرایش دو ردیفه و با زاویۀ 20 درجه نسبت به جریان در جلو تکیهگاه پل مستقر شدند. نتایج این پژوهش نشان میدهد که عملکرد پرههای مستغرق در کاهش آبشستگی اطراف تکیهگاه قابل توجه و موجب حرکت حفرۀ آبشستگی و دور کردن آن از دماغۀ تکیهگاه به سمت مرکز کانال شده است. همچنین، استفاده از پرههای مستغرق با پنج نوع آرایش مختلف نشان میدهد که بهطور متوسط این سازه میتواند 1/60 درصد عمق آبشستگی را در اطراف تکیهگاه پل کاهش دهد. نتایج بهدست آمده همچنین نشان میدهد که بهترین عملکرد را آرایش دو ردیفه موازی دارد که در آن پرههای ردیف اول با فاصلۀ 5 سانتیمتر و ردیف دوم با فاصلۀ 15 سانتیمتر از تکیهگاه قرار میگیرند و موجب کاهش 74/71 درصد از حداکثر عمق آبشستگی شدهاند.
Application of the Submerged Vanes on Reduction of Local Scour around the Bridge Abutment with Rounded Nose
نویسندگان [English]
Ebrahim Nohani2؛
2Deptartment of Hydraulic Structures, Dezful Branch, Islamic Azad University, Dezful, Iran
چکیده [English]
The statistics of bridge failures by US Federal Highway Administration show that the local scour around the bridge abutment is main reason compared to the local scour of piers. Various methods have been suggested for the control and reduction of local scour around the bridge piers and abutment. Using submerged vanes is one of these methods. In this study, the effect of submerged vanes to reduce the local scour around the bridge abutments with rounded nose was studied. Experiments conducted in a compound channel with non-cohesive sediments with diameter (d50) of 1 mm. Experiments carried out in two stages: in first stage without using submerged vanes and at the second stage with the presence of submerged vanes. Two rows of submerged vanes with length of 10 cm, height of 3.33 cm (L/H =3) and with angle of 20° was used. The results showed that the geometric properties of the scour hole in the nose of abutment was similar to the results obtained by other researchers. Results also showed that at all flow conditions submerged vanes reduced the scour hole around the bridge abutment and they moved the scour hole from the near of the abutment to the center of channel. Also the results showed that using submerged vanes averagely reduced 60.1% of the maximum scour depth. Finally the best layout of submerge vanes which had a distance of 5 and 15 cm between first and second rows with abutment, reduced the maximum scour depth by 71.74 percent.
Keywords: Abutment, Compound Channel, Local Scour, Submerged Vanes
کلیدواژه‌ها [English]
Abutment, Compound channel, Local Scour, Submerged Vanes
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