تاثیر شرایط مرزی در کمانش مخازن استوانه یی فولادی با ضخامت متغیر تحت نشست موضعی

استفاده از سازه‌های جدار نازک به دلیل وزن کم و مقاومت بالای آنها، مقبولیت بالایی دارد. به منظور کاهش وزن و قیمت، مخازن با ضخامت متغیر در ارتفاع خود ساخته می‌شوند. نشست فونداسیون در زیر دیواره‌های مخزن به سبب ویژگی خاک رخ می‌دهد، که به 3 مولفه‌ی نشست: یکنواخت، تیلت و موضعی تقسیم می‌شود. در این بین، نشست موضعی بیشترین تاثیر را در پوسته‌ی مخزن دارد، که سبب جابه‌جایی‌های شعاعی بزرگ، کمانش پوسته، و حتی گسیختگی مخزن می‌شود. در پژوهش حاضر، 17 عدد مخزن استوانه‌یی فولادی به روش عددی در نرم‌افزار آباکوس مدل‌سازی شدند و تحت نشست موضعی قرار گرفتند و مقادیر نشست، بار معادل کمانشی و تغییرشکل شعاعی آنها مقایسه شد. نتایج آنالیز غیرخطی حاکی از رفتار مناسب و مقبول مخازن با ضخامت متغیر در قیاس با نمونه‌های با ضخامت ثابت بوده و همچنین حلقه‌ی سخت‌کننده، آثار مثبتی در رفتار کمانشی مخازن مذکور داشته است.

Effect Of Boundary Conditions On Buckling Of Cylindrical Steel Tanks With Variable Thicknesses Under Local Settlement

Cylindrical steel tanks have been used to store various materials and fluids. From a geometrical point of view, steel tanks have a very low thickness compared to the other two dimensions and thus are classified as thinwalled structures. Nowadays, the use of thinwalled structures is very popular. The main reason for this is the low weight and high strength of such structures. In order to reduce the weight and cost of the structure, cylindrical steel tanks can be made with variable thicknesses in height. Changing the thickness of the tank's wall has been considered to reduce weight and economic requirements. Settlement is one of the important issues that must be considered for reservoirs. In general, foundation settlement occurs under the tanks’ walls due to special soil properties, which are divided into three general components: Uniform, Tilt, and Local settlement. In the meantime, local settlement has the greatest impact on the tank’s shell, although it has the lowest value. This component can cause large radial displacements, shell buckling, and even tank’s failure. In this study, 17 steel cylindrical tanks with or without a reinforcing ring on the upper part were modeled in ABAQUS software and placed under local settlement at the edge of their floor. The values of settlement, equivalent buckling load, and their radial deformation were compared to each other. S4R elements (a fournode element with reduced curvature double integral) were used to mesh the tanks. The results of nonlinear analysis indicate that buckling occurs at the lower part of the shell. Moreover, the local settlement causes severe buckling at the site and perpendicular direction of the settlement. Appropriate and acceptable behavior of tanks with variable thickness in comparison with constant thickness and the hardening ring can have positive effects on the buckling behavior of tanks.