تاثیر رفتار غیرخطی خاک و بلند شدن فونداسیون بر پاسخ لرزه ای سازه های تکدرجه آزادی غیرارتجاعی

نوع مقاله : علمی - پژوهشی

نویسندگان

1 استادیار، گروه مهندسی عمران، دانشکده فنی و مهندسی، دانشگاه مازندران، بابلسر، ایران

2 استاد دانشکده مهندسی عمران، دانشگاه صنعتی شریف، تهران، ایران

چکیده

در این مطالعه اثر همزمان بلندشدگی فونداسیون و رفتار غیرخطی در سازه و خاک بر روی عملکرد سیستم‌های خاک و سازه بررسی شده است. مطالعات گذشته نشان داده است که تاثیر اندرکنش خاک و سازه بر عملکرد لرزه‌ای سازه‌ها از طریق معرفی تعدادی پارامتر بدون بعد قابل بررسی می‌باشد. به طور کلی اکثر مطالعات انجام شده در این زمینه با این پیش فرض انجام شده است که فونداسیون اجازه بلندشدگی نداشته و عمدتا رفتار خاک خطی و یا خطی معادل فرض شده است. در این تحقیق نشان داده شده است که این مفهوم با معرفی تعدادی پارامتر بدون بعد جدید، قابل بسط برای سیستم‌های غیر خطی خاک و سازه‌ می‌باشد. محور اصلی این تحقیق بر مطالعه تغییرات نسبت تغییرمکان غیرارتجاعی و شکل‌پذیری سازه، به عنوان بخشی از سیستم خاک و سازه، برای این نوع سیستم‌ها قرار داده شده است. بدین منظور سازه به صورت یک مدل تکدرجه آزادی با رفتار غیرارتجاعی دوخطی در نظر گرفته شده است که بر روی فونداسیون صلب واقع بر فنرهای غیرارتجاعی و میراگرهای گسترده وینکلر قرار دارد. تاثیر رفتار غیرخطی خاک بر روی پاسخ سیستم‌های خاک و سازه به صورت پارامتریک از طریق انجام تحلیل‌های تاریخچه زمانی برای محدوده وسیعی از سیستم‌ها با مشخصات مختلف بررسی شده است. مشاهده شد که اگر چه تغییرمکان کل سیستم خاک و سازه به دلیل رفتار غیرخطی خاک افزایش می‌یابد، اما به طور کلی شکل پذیری سازه به عنوان بخشی از سیستم خاک و سازه نسبت به حالتی که رفتار خاک الاستیک فرض می‌شود،کاهش می‌یابد. از آنجا که نشست ماندگار در زیر فونداسیون از نظر عملکرد سیستم خاک و سازه دارای اهمیت می‌باشد لذا این شاخص مورد بررسی قرار گرفت. نشان داده شد گرچه با کاهش ضریب اطمینان خاک نشست ماندگار افزایش می یابد اما برای مدلهایی با مشخصات کاربردی مقدار آن در محدوده قابل قبول می‌باشد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

The Effects of Nonlinear Behavior of Soil and Foundation Uplift on Seismic Response of Inelastic SDOF Structures

نویسندگان [English]

  • Amir Hossein Jafarieh 1
  • Mohammad Ali Ghannad 2
1 Assistant Professor, Civil Engineering Group, Department of Engineering and Technology, University of Mazandaran, Babolsar, Iran
2 Professor, Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
چکیده [English]

In this research the simultaneously effects of foundation uplift and nolinear behavior of soil were investigated. Previous studies have showed that the effects of soil-structure interaction on seismic performance can be described through introducing a limited number of nondimensional parameters. In most studies it was assumed that the foundation is bonded to the soil and the behavior of the soil is considered to be linear or equivalent linear. In study it is showed that this concept can be extended to the nonlinear soil-structure systems by introducing number of new nondimensional parameters. The main goal of this investigation is to study the variations of nonlinear displacement and ductility of nonlinear soil-structure systems. To achieve this goal, the structure was considered as an nonlinear single degree of freedom with concentrated mass which mounted on rigid foundation rested on distributed dampers and springs. Then the variations of the response of nonlinear soil-structure systems are assessed by conducting nonlinear time history analyses for a wide range of nondimensional parameters. It was shown that the total displacement of soil-structure systems increases because of nonlinear soil behavior but the ductility of the structure as a part of soil-structure system decreases in comparison to the systems with linear soil behavior. So in this study, it was proposed to decrease the safety factor for the design of foundation. Since the permanent settlement of foundation is an important index in performance of soil-structure systems therefore it was calculated for some applicable systems and it is shown that although the permanent settlement of the foundation increases by decreasing safety factor of foundation but the value of permanent settlement is acceptable for ordinary systems.

کلیدواژه‌ها [English]

  • Nonlinear Soil-structure Interaction
  • Nonlinear Displacement Ratio
  • Ductility
  • Safety factor
  • Permanent Settlement
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