مدل‌سازي پي پوسته‌يي مخروطي بتن مسلح با شيب‌هاي مختلف

Analysis of Reinforced Concrete Cone Shell Foundations with Different Slopes

پي‌هاي پوسته‌يي از جمله پي‌هايي هستند كه با توجه به ساختار و شكل‌شان در مقايسه با انواع مسطح داراي ضخامت‌هاي كمتر و مقاومت بيشتري هستند. اين كاهش ضخامت به صرفه‌جويي در مصالح و كاهش هزينه‌ها منجر مي‌شود. علاوه بر اين، شكل خاص آنها باعث افزايش باربري خاك مي‌شود و خصوصيات رفتاري به شكل چشم‌گيري بهبود پيدا مي‌كند. در اين پژوهش با مدل‌سازي، رفتار تعدادي پي پوسته‌يي مخروطي بتن مسلح با ابعاد كاربردي با روش اجزا محدود و نرم‌افزار ABAQUS مورد بررسي قرار گرفته است. در اين تحليل، كه به صورت غيرخطي مصالح است، بتن، خاك و فولادها كاملاً مدل شده‌اند. نتايج عددي نشان مي‌دهند كه پي پوسته‌يي مخروطي در مقايسه با نوع مسطح آن، داراي مقاومت بيشتري است. با افزايش ارتفاع پي مخروطي، مقاومت افزايش مي‌يابد و در ارتفاعي بهينه، بيشترين مقاومت را خواهد داشت.

Shell foundations are structures which derive their strength from geometry rather than mass. This quality enables them to obtain maximum structural integrity with a minimum consumption of construction materials. The use of shells in the field of foundation engineering has drawn considerable interest in different parts of the world. Shell foundations of different shapes have been investigated, on the structural and geotechnical side, at the elastic stage. Because closed-form solutions are extremely complex, especially at ultimate and nonlinear stages, the present investigation has resorted to numerical analysis by the finite element method, using the ABAQUS analysis package. The conical shell is the simplest form of shell that can be employed in foundation engineering, due to its singly curved surface. Reinforced concrete conical shell foundations have been taken up for these studies. There is close agreement between the analytical and test results, and to show that, the results of the test conducted on the elastic model of a conical shell footing by Kurian (2006) have been represented in this paper and compared with finite element results. The behavior of concrete, soil and bars has been studied in nonlinear form for these kinds of shell foundation. The Mohr-Coulomb plasticity model is used to model soils with the classical Mohr-Coulomb yield criterion. The concrete damaged plasticity model provided in ABAQUS is used for the analysis of concrete. The results presented reveal the general superiority of conical shell foundations. The increasing settlement rate of a shell foundation increases with increasing the load. This is because of the nonlinear behavior of soil and concrete and the decrease in stiffness of these materials. Maximum settlement is shown under the center of the shell foundation, beneath the load. The settlement of the edge of the shell is less than at the center of the shell. But, this difference is not so sensible, because of the high stiffness of shell foundations, and is about 9% for the condition of this investigation. The resistance of the system is increased by increasing the angle of the cone wall. This increase has an optimum angle, which is about 40 degrees. There is about 90% increase in bearing capacity for the optimum angle of the reinforced concrete cone shell foundation compared to its flat counterpart.