ضریب ظرفیت باربری Nc پی نواری واقع بر یک‌لایه‌ی منفرد با روش آنالیز حدی ادغام‌شده با المان محدود

نوع مقاله : مقاله کامل پژوهشی

نویسندگان

گروه مهندسی عمران، دانشکده فنی و مهندسی، دانشگاه ارومیه

چکیده

محاسبه حداکثر ظرفیت باربری پی با روش آنالیز حدی، حد بالای ظرفیت باربری دقیق پی را مشخص می‌کند. در این تحقیق ضریب چسبندگی Nc یک پی نواری واقع بر یک‌لایه‌ی منفرد خاک منتهی به سنگ‌بستر محاسبه شده است. بدین منظور از قضیه‌ی حد بالای آنالیز حدی ادغام‌شده با روش المان محدود استفاده شده است. رفتار خاک پلاستیک کامل فرض شده و معیار تسلیم در نظر گرفته شده مدل مور کولمب می‌باشد. بدین ترتیب با دو پارامتر چسبندگی و زاویه اصطکاک داخلی می‌توان توده خاک را توصیف نمود. البته در اینجا فرض شده که چسبندگی خاک در عمق ثابت نبوده و به صورت خطی افزایش می‌یابد و در نهایت ظرفیت باربری از یک فرایند بهینه سازی حاصل شده و بدین منظور از برنامه‌ریزی خطی استفاده می‌گردد. بدین ترتیب معیار مور کلمب در فضای تنش بایستی خطی-سازی شود. ضریب Nc به پارامترهای مختلفی ازجمله زاویه اصطکاک داخلی خاک (φ)، نسبت عمق لایه خاک به عرض پی (h/b) و فاکتور تغییر چسبندگی در عمق (ρ) بستگی دارد. به‌منظور تصدیق نتایج به‌دست‌آمده، جواب‌های حاصل در حالت چسبندگی ثابت با نتایج سایر محققین مقایسه شده است. تأثیر پارامترهای ذکرشده بر روی ضریب Nc در گراف‌های جداگانه رسم شده و در نهایت چارت‌های طراحی محاسبه شده موردبحث قرار گرفته است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Bearing Capacity Factor Nc of Strip Footings on a Single Layer, using Integrated Limit Analysis with Finite Element

نویسندگان [English]

  • Farzin Khanebeygi
  • Kazem Badv
  • Abbas Eslami Haghighat
Department of Civil Engineering, Urmia University, Urmia, Iran
چکیده [English]

Calculating the ultimate bearing capacity of a foundation by limit analysis allows determining the exact upper bound of bearing capacity of the foundation. In the present study, the cohesion coefficient (Nc) of a strip foundation on a single layer of soil overlaying bedrock was calculated. For this purpose, the upper bound of limit analysis combined with finite element method (FEM) was used. The soil behavior was assumed to be plastic and the Mohr-Coulomb failure criterion was used which allows description of soil mass by two parameters of cohesion and internal friction angle. It was assumed that the soil cohesion is not constant with depth and rather increases linearly. Finally, the bearing capacity was obtained using an optimized procedure (i.e., linear programming). In this regard, the Mohr-Coulomb criterion should be linearized in a stress condition. The cohesion depends on different parameters such as friction angle (φ), the ratio of soil depth to foundation width (b/h), and the cohesion variation with depth (ρ). To validate the results, obtained constant cohesion values were compared with those obtained by other researchers. The effect of the parameters on N_c was separately plotted and the calculated design charts were discussed.

کلیدواژه‌ها [English]

  • Limit analysis
  • Linear programming
  • Bearing capacity
  • Upper bound
  • Finite element
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