Dolu rezervuar durumdaki barajların sismik davranış tahminlerine seçilen nümerik model tipinin etkisi

Yıl 2019, Cilt: 21 Sayı: 2, 804 - 821, 28.06.2019

Alper Aldemir

Öz

Barajlar, yılın kurak dönemlerinde toplumların su ihtiyacını karşılamada önemli bir rol oynamakta ve aynı zamanda teknolojik gelişmelerle günümüzde oldukça artan enerji ihtiyacını gidermeye de katkıda bulunmaktadır. Bu nedenle artan nüfus ve teknoloji seviyesiyle, yeni barajların inşası da devam etmektedir. Tasarım aşamasında barajların etkileşimde bulunduğu zemin ve rezervuarın etkileri de dikkate alınmaktadır. Bu etkiler numerik modellere yansıtılırken literatürde farklı teknikler (Westergaard ek kütlesi, Euler akışkan elemanları ve Lagrange akışkan elemanları, vb.) mevcut bulunmaktadır. Bu yaklaşımların barajların sismik tasarımlarına etkileri detaylı bir şekilde incelenmelidir. Bu nedenle, bu çalışmada, barajların tasarımı aşamasında sıklıkla kullanılan farklı modelleme metotlarının barajların modal özelliklerine nasıl etki ettiği irdelenmiştir. Bu amaçla, aynı kesit alanına sahip, farklı kesit geometrilibarajların rezervuarla etkileşimi Euler akışkan elemanı, Lagrange akışkan elemanı ve Westergaard ek kütle yaklaşımları kullanılarak dikkate alınmıştır. Elde edilen baraj modellerinin sismik davranışları elde edilmiş ve birbirleriyle karşılaştırılmıştır. Böylece tasarım aşamasında kullanılan rezervuar baraj gövdesini dikkate almak için kullanılan modelleme metotlarının sismik özellikleri ne ölçüde tahmin edebildikleri incelenmiştir. Gerçekleştirilen analizlerden elde edilen bulgular sonucunda, Lagrange akışkan elemanı ve Westergaard ek kütle yaklaşımları Euler akışkan elemanlı modellere göre %20’yi bulan hata paylarıyla modal özellikleri tahmin edebildiği tespit edilmiştir. Bu hata oranları, yüksek mod etkilerinde oldukça büyük bir artış göstererek ilk mod için gözlemlenen değerin yaklaşık 3 katına çıkmaktadır. Analizlerde kullanılan altı farklı kesit geometrisi sonuçlarına istinaden kesit tipinin sonuçlarda büyük bir farklılık yaratmadığı anlaşılmaktadır. Fakat baraj yüksekliğiyle (ya da artan yüksek mod etkisiyle) doğru orantılı bir şekilde hata paylarında bir miktar artış gözlemlenmiştir.

Anahtar Kelimeler

Ağırlık barajlar, sismik özellikler, rezervuar, modelleme tekniği

Effect of the selected numerical model on the prediction of seismic behaviour of dams with full reservoir conditions

Öz

The dams play an important role in meeting the water needs of societies during the dry periods of the year and at the same time they contribute to supply energy to meet the increasing energy demands due to the advancements in technology. Therefore, the construction of new dams still continues due to the increasing population and the level of technology. In the design phase of gravity dams, the interaction of the dam with the reservoir and the foundation rock should be taken into account. Different techniques (Westergaard’s additional mass, Euler fluid elements and Lagrange fluid elements, etc.) are available in the literature to consider these effects in numerical models. However, the effects of these approaches on the seismic behaviour of dams should be examined in detail. Therefore, in this study, the effect of different reservoir modeling techniques on the seismic properties of concrete gravity dams was investigated. For this purpose, different concrete gravity dam sections were modeled by utilizing different reservoir modeling techniques. Seismic properties of the obtained dam models were determined and compared with each other. As a result, it was determined that different reservoir models predict modal characteristics with error rates of up to 20% compared to Euler fluid element models. These error rates increase nearly three times in high mode effects. In addition, it was observed that the error rates were not dependent on the selected section type. Finally, it has been observed that the predicted accuracy of higher modes is decreasing with the increasing dam height.

Anahtar Kelimeler

Gravity dams, seismic properties, reservoir, modeling technique

Kaynakça

• Carter, B., Structures and land forms: Faults, http://itc.gsw.edu/faculty/bcarter/geomorph/struct/ fault1.htm, (06 October 2017).
• Jackson, J., Earthquake hazards and large dams in western China, Probe International Report, (2012).
• Zangar, C.N., Hydrodynamic pressures on dams due to horizontal earthquake effects, US Bureau of Reclamation, Engineering Monograph, No:11, (1952).
• Raphael, J.N., Design of dams for earthquake resistance, Proceedings of First World Conference on Earthquake Engineering, Berkeley, California (1956).
• Chopra, A.K., Earthquake effects on dams, Ph.D. Thesis, University of California, Berkeley, USA, (1966).
• Nuss, L.K., Matsumoto, N. and Hansen, K.D., Shaken but not stirred – Earthquake performance of concrete dams, Innovative Dam and Levee Design and Construction for Sustainable Water Management, 32nd Annual USSD Conference New Orleans, Louisiana, pp. 1511-1530, (2012).
• Fenves, G. and Chopra, A.K., Simplified earthquake analysis of concrete dams, Journal of Structural Engineering, 113, 8, 1688-1708, (1987).
• Arici, Y., Binici, B. and Aldemir, A., Comparisons of expected damage patterns from two and three dimensional nonlinear dynamic analyses of an RCC dam, Structure and Infrastructure Engineering, 10, 3, 305-315, (2014).
• Bybordiani, M. and Arici, Y., The use of 3D modeling for the prediction of the seismic demands on the gravity dams, Earthquake Engineering and Structural Dynamics, 46, 1769-1789, (2017).
• Aldemir, A., Prediction equations for the fundamental period and mode shape of roller compacted concrete gravity dams considering three dimensional geometry effects, Journal of Earthquake Engineering, (2018). Fenves, G. and Chopra, A.K., Simplified earthquake analysis of concrete gravity dams: Separate hydrodynamic and foundation interaction effects, Journal of Engineering Mechanics (ASCE), 111, 6, 715-735, (1985).
• Fenves, G. and Chopra, A.K., Simplified earthquake analysis of concrete gravity dams: Combined hydrodynamic and foundation interaction effects, Journal of Engineering Mechanics (ASCE), 111, 6, 736-756, (1985).
• Fenves, G. and Chopra, A.K., EAGD-84: A computer program for earthquake response analysis of concrete gravity dams, Report No: UCB/EERC-734, Earthquake Engineering Research Center, University of California, Berkeley, California, USA, (1984).
• Wang, J. and Chopra, A.K., EACD-3D: A computer program for three dimensional earthquake analysis of concrete dams considering spatially - varying ground motion, Report No: UCB/EERC-2008/04, Earthquake Engineering Research Center, University of California, Berkeley, California, USA, (2008).
• Dungar, R., An efficient method of fluid-structure coupling in the dynamic analysis of structures, International Journal for Numerical Methods in Engineering, 13, 1, 93-107, (1978).
• Calayir, Y, Dumanoglu, A.A. and Bayraktar, A., Earthquake analysis of gravity dam-reservoir systems using the Eulerian and Lagrangian approaches, Computers and Structures, 59, 5, 877-890, (1996).
• Westergaard, H.M., Water pressures on dams during earthquakes, Transactions of ASCE, 98, 418–434, (1933).
• ANSYS Theory Manual, Theory reference for the mechanical APDL and mechanical applications, SAS IP Inc., (2016).
• ANSYS Inc., Basic Analysis Guide for ANSYS, SAS IP Inc, (2016).
• Aldemir, A., Prediction equations for the fundamental period and mode shape of roller compacted concrete gravity dams considering three dimensional geometry effects, Journal of Earthquake Engineering, 2018.
• Sevim, B., Altunisik, A.C., Bayraktar, A., Akköse, M., and Calayir, Y., Water length and height effects on the earthquake behavior of arch dam-reservoir-foundation systems, KSCE Journal of Civil Engineering, 15, 2, 295-303, 2011.
• Kuo, J.S.H., Fluid – structure interactions: Added mass computations for incompressible fluid, Report No: UCB/EERC-82/09, Earthquake Engineering Research Center, University of California, Berkeley, California, (1982).