كليدواژه :
بار بركنش , سد وزني بلند , آيين نامه و اجزاي محدود , اعتبار روش هاي متداول اعمال بار بركنش
چكيده فارسي :
يكي از عوامل مهم و تاثيرگذار در پايداري سدهاي وزني و طراحي آن، ميزان بار بركنش ميباشد. آيين نامه هاي مختلف با توجه به پارامترهايي نظير ميزان ارتفاع آب در مخزن و نيز پايين دست سد، يك توزيع چند خطي را براي بار بركنش در زير سد در نظر مي گيرند. در اين تحقيق، مدلسازي از چند سد وزني از نوع پاين فلت به منظور حساسيت سنجي اينگونه توزيع ها نسبت به ارتفاع سد صورت گرفت. در كليه تحليل ها، بدنه ي سد كاملاً نفوذ ناپذير در نظر گرفته شده و توده سنگ پي به صورت يك محيط همگن و همسان فرض شده است. از مقايسه بين تنش هاي ايجاد شده در محل اتصال سد و پي در اين مدلها، با تنش هاي حاصل از اعمال توزيع بار بركنش در زير سد مطابق آيين نامه اداره مهندسي ارتش آمريكا مشخص شد كه ميزان خطاي اين گونه الگوهاي رايج با ارتفاع سد رابطه ي مستقيم دارد. به طوريكه با افزايش ارتفاع سد ميزان خطاي مربوط به تنش در بخش حساس شالوده سد حتي تاحدود 40 درصد رشد مي كند. در اين گروه از سد ها اين خطا به 12 برابر خطاي قابل انتظار در سدهاي كوتاه تر نيز افزايش پيدا مي كند. اين مساله در برخي موارد مي تواند ايمني سد را كاملا تهديد كند. اين تحقيق الگوي پيشنهادي ديگري جهت اعمال بار بركنش در زير سدهاي وزني معرفي كرده و ضرورت استفاده از روش هاي دقيق تر در برآورد ميزان بار بركنش در زير سدهاي وزني بلند را نشان مي دهد.
چكيده لاتين :
Gravity dams are vital structures whose proper design and evaluation for stability are quite important. Effective issues on the stability of gravity dams are the uplift force and its distribution below the dam base. The uplift load pattern and distribution according to common codes are influenced by some factors such as head and tail water, assuming a segmented linear load distribution below the dam. In this research, to investigate the sensitivity of the load pattern to dam height, a number of gravity dams of Pine Flat type with different heights and their foundations are modeled. Coupled p-u finite element analysis is performed accounting for the seepage and stress field simultaneously. Dam body is considered to be completely impervious. The foundation rock is assumed as homogeneous and uniform, in terms of elasticity and permeability. The stresses generated in the dam interface for each case of the coupled hydro-mechanical analysis is compared against that of the conventional load pattern according to the USACE regulation for the same dam model. It was found that the error magnitude due to the conventional pattern has a direct relationship with the dam height. As the dam height increases, the amount of error of calculated stress increases. In particular, the error at the critical zones of the foundation such as at the dam heel, may raise even up to 40%. In the group of dams studied, the error increases even up to 12 times in respect to the expected error in the shorter dams. The deficiency could in some cases completely affect the safety of the dam. This research indicates the necessity of using more accurate methods of estimating uplift load under high gravity dams. Gravity dams are vital structures whose proper design and evaluation for stability are quite important. Effective issues on the stability of gravity dams are the uplift force and its distribution below the dam base. The uplift load pattern and distribution according to common codes are influenced by some factors such as head and tail water, assuming a segmented linear load distribution below the dam. In this research, to investigate the sensitivity of the load pattern to dam height, a number of gravity dams of Pine Flat type with different heights and their foundations are modeled. Coupled p-u finite element analysis is performed accounting for the seepage and stress field simultaneously. Dam body is considered to be completely impervious. The foundation rock is assumed as homogeneous and uniform, in terms of elasticity and permeability. The stresses generated in the dam interface for each case of the coupled hydro-mechanical analysis is compared against that of the conventional load pattern according to the USACE regulation for the same dam model. It was found that the error magnitude due to the conventional pattern has a direct relationship with the dam height. As the dam height increases, the amount of error of calculated stress increases. In particular, the error at the critical zones of the foundation such as at the dam heel, may raise even up to 40%. In the group of dams studied, the error increases even up to 12 times in respect to the expected error in the shorter dams. The deficiency could in some cases completely affect the safety of the dam. This research indicates the necessity of using more accurate methods of estimating uplift load under high gravity dams.
