اثر انعطاف‌پذیری پی بر ظرفیت قاب‌های بتن‌آرمه حاوی دیوار برشی

نوع مقاله : مقاله پژوهشی

نویسنده

دانشکده مهندسی عمران- دانشگاه تفرش- تفرش- ایران

چکیده

لحاظ نمودن مدل خاک-پی-سازه باعث تغییر در پاسخ لرزه‌ای سازه‌ها می‌گردد. با وجود این‌که زمان تناوب و میرایی سازه با در نظرگرفتن اندرکنش تغییر یافته و به واسطه انعطاف­پذیری خاک باعث کاهش نیروهای ورودی می‌گردد، لیکن این فرضیه در تمامی حالات صحت نداشته و می‌تواند باعث تخمین غیر محافظه‌ کارانه تقاضای لرزه‌ای گردد. هدف از مقاله حاضر بررسی اثر انعطاف‌پذیری پی بر ظرفیت قاب­های خمشی بتن­آرمه حاوی دیوار برشی می­باشد. بدین منظور از روش ساده و کارآمد و در عین حال با دقت مناسب تیر مستقر بر خاک غیرخطی وینکلر استفاده شده است. در این راستا قاب­های خمشی ٣، 6 و 10 طبقه بتنی حاوی دیوار برشی مستقر بر خاک‌های نرم، متوسط و سخت طراحی شده است. پس از پیاده­سازی مدل­‌ها برای حالت‌های پایه صلب و انعطاف­‌پذیر در نرم­افزار Opensees، تحلیل دینامیکی فزاینده تحت سناریوهای لرزه­ای مناسب انجام شده است. مقایسه نتایج حاصل از تحلیل دینامیکی فزاینده هر یک از قاب­‌ها بیانگر تأثیر چشمگیر پدیده اندرکنش خاک- پی- سازه بر منحنی‌های حاصل از این تحلیل و ظرفیت قاب می‌باشد. عدم در نظر گرفتن انعطاف­پذیری پی منجر به ورود خطاهای بزرگ در روند طراحی و بهسازی سیستم‌های اندرکنشی می‌گردد. چرا که سیستم به واسطه انعطاف‌پذیری پی، قبل از رسیدن به ظرفیت مورد انتظار متناظر با فرض پایه صلب تخریب می‌گردد. این موضوع با نرم‌تر شدن خاک و افزایش ارتفاع قاب‌ها شدت بیشتری می‌یابد. به گونه­ای­ که قاب­های 3 و 6 طبقه مستقر بر خاک نرم با پایه منعطف به ترتیب در شتاب طیفی معادل 52% و 45% شتاب طیفی نظیر پایه گیردار به ظرفیت خود می­‌رسند. 

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Effect of Foundation Flexibility on the Capacity of Concrete Moment Frames with Shear Wall

نویسنده [English]

  • Elham Rajabi
Department of Civil Engineering/ Tafresh University/ Tafresh/ Ian.
چکیده [English]

Considering the soil-foundation-structure interaction (SFSI) in the structural modeling procedure can change the seismic structural response. However, the SFSI effects are mostly ignored in the analysis procedure of structures, as a general engineering belief regarding its conservative effects. This conservation is not always the case, although the period and the damping of structures change by considering SFSI effects and consequently, the seismic demand decreases. The aim of this paper is to evaluate the influence of foundation flexibility on the capacity of concrete moment frames with the shear wall. For this purpose, the beam on nonlinear Winkler foundation approach is used, which is a simple and efficient method. First, a collection of 3, 6 and 10 storied reinforced concrete moment resisting frames founded on soft, medium and hard soils are designed based on FEMA450. After the implementation of frames in Opensees software, a set of seismic scenarios are selected. In the following, each frame that has been founded on the soft, medium and hard soil is analyzed for the case of fixed-base and the flexible-base assumption by incremental dynamic analysis (IDA). A comparison is made between the results of each frame in the flexible-base and fixed-base conditions. The results show that the consideration of the SFSI effects can significantly influence the IDA curves and decrease the structural capacity of frames. So that dynamic instability will occur before the expected capacity corresponding to fixed-base assumptions has been achieved. This instability increases with increasing shear wave velocity of soils and height of frames. For example, 3 and 6 storied frames with the flexible base, which have been founded on soft soil, reach ultimate capacity in 52% and 45% of spectral acceleration corresponding to fixed base, respectively.

کلیدواژه‌ها [English]

  • Soil-Foundation-Structure Interaction
  • Incremental dynamic analysis
  • Shear Wall
  • Seismic Scenarios
  • Nonlinear Winkler Foundation
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