اثر اندركنش آب- سازه بر پاسخ لرزه اي سد و ديوار حايل

Investigation of the Effect of Fluid-Structure Interaction on the Dynamic Response of Retaining Walls and Dams

در تحليل لرزه اي سازه هاي در تماس با آب، عوامل مختلفي بر پاسخ نهايي سازه تاثيرگذار هستند. يكي از اين عوامل لحاظ نمودن تاثير مستقيم مخزن است كه به ويژه در هنگام وقوع زلزله هاي شديد و در سازه هاي بلند مي-تواند حايز اهميت باشد. با توجه به اين امر مطالعات گوناگوني در زمينه تحليل اندركنش سازه- سيال در علوم مهندسي مختلف ارايه گرديده است كه در اين گفتار تحقيقات انجام گرفته در زمينه مهندسي عمران با تكيه بيشتر بر انواع سدها مورد توجه خواهد بود. در تحقيق حاضر ابتدا روشهاي مختلف تحليل مسايل اندركنش سازه- سيال بررسي و سپس نمونه هايي از اعمال اين روشها با استفاده از مطالعات موردي انجام گرفته در زمينه بررسي اثر وجود مخزن بر سازه هايي نظير ديوار حايل، سدهاي بتني، سدهاي سنگريزه اي با پوشش بتني و سدهاي خاكي ارايه خواهد شد. به دليل گسترش روشهاي عددي در سالهاي اخير، در تحقيق حاضر مطالعات صورت پذيرفته با روشهاي عددي با تاكيد بيشتري مورد بررسي قرار مي-گيرد و بر مبناي ادبيات فني موجود توصيه هاي كلي در مورد محدوده تاثير اندركنش سد- مخزن ارايه مي گردد. همچنين مثالهايي از تحليل هاي انجام گرفته بر روي سدهاي بتني وزني و سدهاي CFRD كه توسط مولفين با نرم افزار ADINA انجام گرفته است، ارايه و نتايج آن با نتايج موجود در ادبيات فني مقايسه خواهد گرديد.

There are many parameters that influence the dynamic response of structures in contact with fluid medium. One of these parameters is the direct effect of reservoir, especially for high structures during severe earthquakes, so there are an extensive amount of publications about the analysis of fluid-structure interaction systems in different engineering branches. In this research, studies in the field of civil engineering with an emphasis on dams will be considered. The different methods of analysis of the fluid-structure interaction problems are reviewed and then some case studies for structures such as retaining walls, concrete, CFR and embankment dams, are discussed. Due to the development of numerical methods in recent years, the studies done using such methods are considered with more emphasis. However, analytical methods such as Westergard and Chopra cases are presented and discussed in this paper. Studies in the field of concrete dams are presented in two divisions as modeling approaches and boundary condition effects. Then the studies about the seismic interaction of reservoir-CFR dams are presented in the related section. Also analysis of seismic coupled reservoir-structure systems for a concrete dam and a CFR dam, which have been conducted by the authors with ADINA software, are presented and compared with the results of the previous studies. This comparison shows the accuracy of the results of ADINA software in the field of dynamic coupling of water-structure systems for concrete and CFR dams. Finally, the previous studies for the dynamic interaction of embankment dam-reservoir system are presented and the related results are discussed. It is concluded from reviewing the previous study that the amount of hydrodynamic force in the fluid domain is a function of the frequency content of incident seismic wave and the ratio of the natural frequency of dam to reservoir one. Therefore, there is not a certain height restriction for unconsidering the effect of interaction of reservoir-dam. Also, if the frequency content of energy of seismic wave is less than the natural frequency of reservoir, the effect of considering the coupled water-structure system would be less. Consequently, the final results of such system would be less affected by the reservoir. As another result, if the ratio of the natural frequency of reservoir to dam is almost "2", the interaction of reservoir-structure has no considerable effect on the final seismic response of coupled system. In the special case of CFR and embankment dams, there are fewer researches in comparison with concrete dams. The main reason can be related to the low slope of upstream face of the dam which reduces the hydrodynamic force of the reservoir. But there are not sufficient available researches that improve the accuracy of such arguments in many different conditions of incident wave (magnitude of PGA, the frequency content of seismic wave, spatial ground motion condition), and variation of some parameters such as per- meability coefficient of shell materials, height of dam, and slope of upstream face. Therefore, it seems that in the future, more studies should be done in the field of embankment dam-reservoir coupled system.