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Akarsular üzerindeki köprülerin menbasında oluşan kabarma miktarının hesabında U.S. federal highway administration ve U.S. army corps of engineers HEC-2 yöntemlerinin Türkiyedeki bazı köprüler için karşılaştırılması

Başlık çevirisi mevcut değil.

  1. Tez No: 50276
  2. Yazar: GALİP SEÇKİN
  3. Danışmanlar: PROF.DR. TEFARUK HAKTANIR
  4. Tez Türü: Yüksek Lisans
  5. Konular: İnşaat Mühendisliği, Civil Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1996
  8. Dil: Türkçe
  9. Üniversite: Çukurova Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 86

Özet

36 ÖZET Bir akarsuyun belirli bir kesitinde bir köprünün varlığı akım üzerinde, sürtünme kayıplarının yamsıra, ekstra enerji kayıplarına neden olur ve bu fazla enerji ihtiyacı köprünün menba yüzünden bir köprü açıklığı mesafe kadar menba tarafındaki bir kesitte akım derinliğindeki ekstra potansiyel enerji birikimiyle karşılanır. Bu kesitte kabarmış olan derinlik köprünün mevcut olmadığı normal haldeki akım derinliğinden daha fazladır ve ikisi arasındaki fark köprü kabarması olarak tanımlanır. Modern köprülerde köprü kolonlarının kesit alanları genelde küçüktür. Bu yüzden, bu ekstra enerji kaybının büyük bir kısmı, akımın normal akarsu kesitine nazaran daha dar olan köprü açıklığından geçmek için daralması ve özellikle açılmasıesnasında oluşur. Dolayısıyla, net köprü uzunlukları normal taşkın kesitinden daha dar olan modern köprüleri içeren taşkın durumunda akarsu parçalarında, yaklaşım şeddelerinin köprü kabarması miktarına etkisi, köprü ayaklarının etkisinden daha fazladır. O halde, köprü kabarmasının doğru olarak hesaplanabilmesi için bir köprü ile daraltılmış olan akarsu parçasından bir taşkm debisinin geçişi snasında karşılaştığı daralma ve açılma kayıplarının doğru değerlendirilmesi gerekmektedir. Tasarım debisinden daha büyük bazıdebilerde akım köprünün üzerinden aşabilir ve bu durumda köprü hem geniş-kretli savak ve hem de orifis gibi davranabilir. Köprü üzerinden geçmeyen akım hali için yine bazıçok kısa köprülerin altındaki bu çok dar kesit boğulmuş akıma neden olabilir. Diğer bir deyişle, köprü altında kritik akım oluşabilir ve köprüyü terkeden akımın fazla enerjisi açılan bir hidrolik sıçrama tarafından eritilebilir. Burada, sadece yukarıdaki paragrafta özetlenen tür akım incelenmiş ve diğer tür akımlar bu çalışmanın kapsamı dışında bırakılmıştır. Köprü yaklaşım şeddeleri ile köprü ayaklarının köprü civarında taşkın durumunda akarsu su yüzü profiline etkisinin hesabı için 1955-60 yıllanarasmda kapsamlı laboratuvar modelleri üzerinde yapılan deneysel çalışmalar sonucu geliştirilmiş U.S. Federal Highway Administration'm (FHA) metodu, 1964-65 yıllarında gerçek köprüler civarında yapılan detaylı prototip ölçümlerindeki köprü kabarmasının ancak yansı kadarını hesaplayınca, söz konusu metodun tasarım grafikleri gerçek dataya göre düzeltilmiştir. U.S. Army39 The computer program HEC-2 of the Hydrologic Engineering Center of U.S. Army Corps of Engineers for computing water surface profiles in natural streams however, computes the bridge backwater in a different way as a combination of Yarnell's pier-effect formula and the classical energy equations for stage prediction by accounting for the contraction and expansion losses using contraction and expansion coefficients of 0.3 and 0.5, respectively. HEC-2 is a renowned package program for computing water surface profiles, and it is used widely all over the world. In this study, the bridge backwaters for 100 different cases resulting from various permutations of five different flow rates, two different channel bottom slopes, and two different wall roughnesses of five real bridges at different locations in Turkey were computed separately both by the method of FHA and by HEC-2, which were arbitrarily picked and whose geometrical and hydraulic data were obtained from the State Highway Directorate of Government of Turkey. Assuming the backwater given by the method of FHA was correct, the magnitudes of the contraction and expansion coefficients of HEC-2 were determined by a trial-and-error approach by running the HEC-2 program many times until HEC-2 yielded the same value for the backwater for the same case as the method of FHA. In conclusion, in order to have HEC-2 compute a water surface profile in a reach crossed by a bridge having a shape similar to the profiles actually observed in many such reaches in the years 1964 and 1965 and a backwater value close to the actually observed ones in those prototype measurements, the magnitude of the contraction loss coefficient should be 0.05 instead of the suggested value of 0.3, and the magnitude of the expansion loss coefficient should be much greater than the suggested value of 0.5. Here, it was determined that the value of the expansion coefficient is not constant, but it varies as a function of three relevant properties, and the most meaningful regression equation resulting from 100 data points obtained from 100 realistic simulations of this study is: Cexp = -5.28 * log (AR) + 4.93 * PR - 0.744

Özet (Çeviri)

39 The computer program HEC-2 of the Hydrologic Engineering Center of U.S. Army Corps of Engineers for computing water surface profiles in natural streams however, computes the bridge backwater in a different way as a combination of Yarnell's pier-effect formula and the classical energy equations for stage prediction by accounting for the contraction and expansion losses using contraction and expansion coefficients of 0.3 and 0.5, respectively. HEC-2 is a renowned package program for computing water surface profiles, and it is used widely all over the world. In this study, the bridge backwaters for 100 different cases resulting from various permutations of five different flow rates, two different channel bottom slopes, and two different wall roughnesses of five real bridges at different locations in Turkey were computed separately both by the method of FHA and by HEC-2, which were arbitrarily picked and whose geometrical and hydraulic data were obtained from the State Highway Directorate of Government of Turkey. Assuming the backwater given by the method of FHA was correct, the magnitudes of the contraction and expansion coefficients of HEC-2 were determined by a trial-and-error approach by running the HEC-2 program many times until HEC-2 yielded the same value for the backwater for the same case as the method of FHA. In conclusion, in order to have HEC-2 compute a water surface profile in a reach crossed by a bridge having a shape similar to the profiles actually observed in many such reaches in the years 1964 and 1965 and a backwater value close to the actually observed ones in those prototype measurements, the magnitude of the contraction loss coefficient should be 0.05 instead of the suggested value of 0.3, and the magnitude of the expansion loss coefficient should be much greater than the suggested value of 0.5. Here, it was determined that the value of the expansion coefficient is not constant, but it varies as a function of three relevant properties, and the most meaningful regression equation resulting from 100 data points obtained from 100 realistic simulations of this study is: Cexp = -5.28 * log (AR) + 4.93 * PR - 0.74439 The computer program HEC-2 of the Hydrologic Engineering Center of U.S. Army Corps of Engineers for computing water surface profiles in natural streams however, computes the bridge backwater in a different way as a combination of Yarnell's pier-effect formula and the classical energy equations for stage prediction by accounting for the contraction and expansion losses using contraction and expansion coefficients of 0.3 and 0.5, respectively. HEC-2 is a renowned package program for computing water surface profiles, and it is used widely all over the world. In this study, the bridge backwaters for 100 different cases resulting from various permutations of five different flow rates, two different channel bottom slopes, and two different wall roughnesses of five real bridges at different locations in Turkey were computed separately both by the method of FHA and by HEC-2, which were arbitrarily picked and whose geometrical and hydraulic data were obtained from the State Highway Directorate of Government of Turkey. Assuming the backwater given by the method of FHA was correct, the magnitudes of the contraction and expansion coefficients of HEC-2 were determined by a trial-and-error approach by running the HEC-2 program many times until HEC-2 yielded the same value for the backwater for the same case as the method of FHA. In conclusion, in order to have HEC-2 compute a water surface profile in a reach crossed by a bridge having a shape similar to the profiles actually observed in many such reaches in the years 1964 and 1965 and a backwater value close to the actually observed ones in those prototype measurements, the magnitude of the contraction loss coefficient should be 0.05 instead of the suggested value of 0.3, and the magnitude of the expansion loss coefficient should be much greater than the suggested value of 0.5. Here, it was determined that the value of the expansion coefficient is not constant, but it varies as a function of three relevant properties, and the most meaningful regression equation resulting from 100 data points obtained from 100 realistic simulations of this study is: Cexp = -5.28 * log (AR) + 4.93 * PR - 0.74440 where, Cexp: expansion loss coefficient, AR is the ratio of (area of the constricted section)^-(totaI area of the natural cross-section) computed for the uniform flow profile, PR is the ratio of (total cross-sectional area of the piers) -*. (area of constricted section) under normal water surface elevation, again for the uniform flow case, and the determination coefficient of the equation was 78 %. The above formula is not presented as the final model depicting the magnitude of the expansion loss coefficient. A similar and more meaningful expression could be obtained by analyzing more data either of prototype measurements or of laboratory model measurements having true dynamic similarity. However, it is the strong conviction of this study that the water surface profiles which would be computed by HEC-2 with the contraction and expansion loss coefficient values presented already in this study would be more correct than the profiles which are computed with the values suggested in the recent users' manual of HEC-2.

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