توسعه‌ي نرم‌افزار تحليل ديناميكي غيرخطي سيستم سد بتني- مخزن- فونداسيون ناپيوسته با شرايط مرزي جاذب و متحرك

Development of Numerical Software for Nonlinear Dynamic Analysis of a Concrete Dam-Reservoir-Foundation System, with Suitable Absorption and Moving Boundary Conditions

مدل‌سازي عددي سدهاي بتني قوسي در سيستم كوپل با مخزن و تكيه گاه، يكي از پيچيده ترين مباحث در حوزه‌ي مهندسي محسوب مي شود. اين پيچيدگي ناشي از عوامل مختلفي چون اندركنش محيط ها، رفتار غيرخطي مصالح و نيز تاثير درزهاي انقباضي بدنه و ناپيوستگي هاي تكيه گاه سنگي است. در اين مطالعه، يك نرم‌افزار المان محدود براي تحليل ديناميكي غيرخطي سدهاي بتني توسعه يافته است. ويژگي هاي برنامه‌ي عددي شامل: مدل‌سازي اندركنش محيط ها، مدل‌سازي رفتار غيرخطي هاي مصالح، المان هاي هندسي و تماسي و امكان اعمال شرايط مرزي مناسب با مدل‌سازي تنش‌هاي برجاي تكيه‌گاهي است. پس از صحت‌سنجي جنبه هاي مختلف برنامه، يك نمونه‌ مطالعه‌ي موردي سد بتني تحت بارگذاري لرزه‌يي با احتساب عوامل موثر مورد توجه قرار گرفته است. اين نوشتار بر نقش و اهميت مدل‌سازي ناپيوستگي ها و شرط مرزي مناسب بخش تكيه گاه سنگي در تحريك لرزه ‌يي سدهاي بتني قوسي تاكيد دارد و نتايج حاصل نيز مويد اين موضوع است.

Numerical modeling of concrete arch dams by considering dam-reservoir-abutment interaction is a complicated subject in the field of engineering. This complexity is due to different factors, such as interaction between different media, the nonlinear behavior of concrete and bedrock, expansion joints in the dam body, faults and major joints in the abutment rock and etc. In past years, extensive research in various fields related to the analysis and design of concrete dams has been undertaken, but the need for more accurate modeling of abutments in a coupling system, considering mass, flexibility and non-homogeneity of a discontinuous rock foundation, is still required. Furthermore, the structural strength of an arch dam under ground motion is strongly dependent on the stability and strength of its abutments. Actually, even high safety margins for unexpected ground motion do not guarantee the stability of a dam if it is established on an uncertain foundation. In this research, finite element software for nonlinear dynamic analysis of concrete dams is developed that can simulate the interactive situation and precisely evaluate the dam response. Some features of the developed numerical program are its ability to model water-structure-rock interactions, the nonlinear behavior of concrete and abutment rock, the contact behavior of dam expansion joints and foundation discontinuities, appropriate boundary conditions for the far end cut out of the reservoir and the rock foundation, and the proper abutment in-situ stresses. The present study sets out to investigate the non-linear seismic response of a dam-reservoir-foundation system, taking into consideration the effects of a discontinuous rock foundation. After verification of different aspects of the program, a typical case study of a concrete dam (Karun 4 Dam) under seismic loading, considering its effective factors, is studied. The analysis results approve the importance and significance of different factors, such as modeling the discontinuous flexible massive foundation, along with appropriate absorption and moving boundary conditions, on the seismic response of dams, leading to a more precise design of new dams and better control of existing ones.