IJE TRANSACTIONS A: Basics Vol. 31, No. 7 (July 2018) 1020-1027    Article in Press

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N. Farhadi, H. Saffari and and P. Torkzadeh
( Received: December 25, 2017 – Accepted in Revised Form: February 18, 2018 )

Abstract    In structural analysis, the base of structures is usually assumed to be completely rigid. However, the combination of foundation and the subsurface soil, makes in fact a flexible-base for the soil-structure system. It is well-known that the structural responses can be significantly affected by incorporating the Soil-structure Interaction (SSI) effects. The aim of the present study is to provide more accurate structural responses analysis by considering the influence of SSI. It is noteworthy that the input ground motion records imposed to the combination of the soil, foundation and structure were selected in a such way that their characteristics were completely matched with the subsurface soil of structures. For this purpose, 3, 6, 9, 12, 15, 18 and 20-storey structures resting on a shallow foundation were selected and the concept of Beam on Nonlinear Winkler Foundation (BNWF) model is employed. The seismic responses of these structures were calculated based on the five different types of soil and the outcomes were compared with those from fixed-base structures. A set of 35 ground motion excitations recorded on different soil types, is selected which categorized to 5 sets consist of 7 records. Non-Linear Response History Analysis (NL-RHA) was performed and radiation damping considered for all of the structures and soil types. The results clearly showed that the inter-storey drift ratio was reduced in lower stories considering SSI effects. These effects are strongly increased, especially with increasing the slenderness ratio of the structures and softening the subsurface soil. Finally, the period lengthening ratio of studied structures, for various soil types was investigated.


Keywords    Soil-structure Interaction; Inter-story Drift; Beam on Nonlinear Winkler Foundation; Radiation Damping; Non-Linear Response History Analysis


چکیده    در تحلیل سازهها معمولا تکیهگاه سازه کاملا گیردار در نظر گرفته میشود. این در حالی است که در واقعیت، فونداسیون و خاک زیر آن تشکیل یک بستر انعطافپذیر را برای سیستم اندرکنش خاک و سازه تشکیل میدهند. کاملا آشکار است که پاسخهای سازهای متاثر از اندرکنش بین خاک و سازه میباشند. هدف از مطالعه حاضر، بررسی دقیقتر پاسخ سازهها با در نظر گرفتن اثر اندرکنش خاک و سازه میباشد.نکته مهم در این تحقیق این است که شتابنگاشتهای وارده به مجموعه سازه، فونداسیون و خاک زیر آن، به نحوی انتخاب گردیدهاند که مشخصات آنها کاملا منطبق با خاک زیر سازه میباشد. برای این منظور ساختمانهایی با تعداد طبقات 3، 6، 9، 12، 15، 18 و 20 که روی فونداسیون سطحی قرار دارند در نظر گرفته شدهاند.همچنین از مدل تیر بر فونداسیون غیر خطی وینکلر استفاده گردیده است. پاسخهای لرزهای این سازهها بر روی پنج دسته خاک مختلف محاسبه و با پاسخهای سازهای با پایه گیردار مقایسه شدهاند. یک مجموعه شامل 35 شتابنگاشت که بر روی خاکهای مختلف ثبت شدهاند، در قالب 5 دسته 7 تایی طبقهبندی گردیدهاند.این سازهها تحت تحلیل تاریخچه زمانی دینامیکی غیر خطی با در نظر گرفتن میرایی شعاعی، مورد بررسی قرار میگیرند.نتایج نشان میدهد که نسبت دریفت بین طبقهای در طبقات پایین با در نظر گرفتن اثرات اندرکنش خاک و سازه، کاهش مییابد. با افزایش نسبت لاغری سازهها و همچنین نرمتر شدن خاک زیرین آنها، این اثرات چشمگیرتر میشوند. در نهایت نسبت افزایش دوره تناوب سازهها در خاکهای مختلف مورد بررسی قرار میگیرد.


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