Abstract




 
   

IJE TRANSACTIONS A: Basics Vol. 31, No. 7 (July 2018) 1346-1354    Article in Press

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  EVALUATION OF SEISMIC BEHAVIOR OF STEEL MOMENT RESISTING FRAMES CONSIDERING NONLINEAR SOIL-STRUCTURE INTERACTION
 
N. Farhadi, H. Saffari and P. Torkzadeh
 
( Received: December 25, 2017 – Accepted: February 18, 2018 )
 
 

Abstract    In structural analysis the base of structures is usually assumed to be rigid. It is well-known that structural responses can be significantly affected by incorporating 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. The input ground motions are selected in a such way that their characteristics are completely matched with the subsurface soil of structures. For this purpose, 3, 6, 9, 12, 15, 18 and 20-storey structures are selected and the concept of Beam on Nonlinear Winkler Foundation (BNWF) model is employed. Seismic responses of these structures are calculated based on the five different types of soil and are compared with those from fixed-base structures. A group of 35 ground motion excitations recorded on different soil types, are selected which categorized to 5 sets consist of 7 records. Non-Linear Response History Analysis (NL-RHA) is performed and for all of the structures and soil types investigated, the radiation damping is considered. The results show that the inter-storey drift ratio is reduced in lower stories considering SSI. These effects are strongly increased, especially with increasing the slenderness ratio of the structures and softening the subsurface soil.

 

Keywords    SSI, inter-story drift, BNWF, radiation damping, NL-RHA

 

چکیده    در تحلیل سازه­ها معمولا تکیه­گاه سازه گیردار در نظر گرفته می­شود. 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. شتاب­نگاشت­ها 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 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.

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