اثر مولفه هاي دوراني زلزله در پاسخ ديناميكي سدهاي بتني وزني با احتساب اندركنش سد و مخزن

Effect of Rotational Components of Earthquakes on Dynamic Response of Concrete Gravity Dams Considering Reservoir Interaction

هدف اين پژوهش، ارايه‌ي فرمول‌بندي مناسب به منظور بررسي اثر هم‌زمان مولفه‌هاي انتقالي و دوراني حركت زمين در پاسخ سدهاي بتني وزني با احتساب اندركنش سد و مخزن به روش اجزا محدود است. بدين منظور، مولفه‌هاي دوراني حركت زمين با استفاده از مولفه‌هاي انتقالي آن با درنظرگرفتن سرعت امواج وابسته به بسامد توليد مي شوند. سپس اين مولفه‌ها به روش‌هاي مناسب به مدل اجزا محدود سيستم سد- مخزن اعمال و پاسخ ديناميكي آن با استفاده از روش نيومارك و با درنظرگيري تغييرمكان به عنوان متغير مجهول در گره‌هاي شبكه‌ي اجزا محدود كل سيستم كه به روش لاگرانژي-لاگرانژي معروف است، به دست مي‌آيد. نتايج به دست‌آمده نشان مي دهد كه با توجه به بيشينه‌ي مقدار مولفه‌هاي دوراني و نيز طيف محتواي بسامدي آنها، ممكن است اين مولفه‌ها به طور قابل توجهي، تحت شرايط خاص، موثر باشند.

Rotational components of ground motion including rocking and torsional components have been eccentrically ignored for a long time, first, because the rotational effects were thought to be small for structures and, second, due to their small amplitude, they cannot be measured using standard seismic devices. Recently it has been shown that the rotational component of ground motion can have noticeable effects on the dynamic response of structures, and many structural failures and the damage caused by earthquakes can be linked to differential and rotational ground motion. The main purpose of this paper is presentation of a proper formulation for dynamic analysis of concrete gravity dams under the correlated translational and rotational components of ground motion due to earthquakes. The rocking component of earthquake acceleration has been obtained using the corresponding available translational components, based on transversely isotropic elastic wave propagation in 2-D space and the classical elasticity theorem between rotational and translational motions. Using the mentioned approach, it becomes possible to consider frequency dependent wave velocities and the incident wave angle of the earthquake to generate the rotational components of ground motion. For this purpose, two translational components of different earthquake accelerations have been adopted to generate their relative rotational components, based on SV and SH wave incidence. The results are compared with other work and show very good agreement. Using translational and obtained rotational components of ground motion, a dynamic analysis of the Pine Flat dam has been performed for six earthquake accelerations. Analyses have been done using the finite element method, considering dam-reservoir interaction. The dam and reservoir are modeled using a Lagrangian approach, and different water levels of the reservoir are considered. The material behavior of the dam and reservoir is considered to be elastic, linear, isotropic and homogeneous, and, also, the foundation is assumed to be rigid. Results are shown that depend on maximum rocking components and their frequency content. Content, these components can be effective on the linear dynamic response of concrete gravity dams and cannot be negligible in some cases.