Abstract




 
   

IJE TRANSACTIONS C: Aspects Vol. 28, No. 3 (March 2015) 338-349   

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  A CONTINUUM SHELL-BEAM FINITE ELEMENT MODELING OF BURIED PIPES WITH 90-DEGREE ELBOW SUBJECTED TO EARTHQUAKE EXCITATIONS
 
M. Saberi, F. Behnamfar and M. Vafaeian
 
( Received: July 07, 2014 – Accepted: December 18, 2014 )
 
 

Abstract    In the current work, the seismic analysis of bent region in buried pipes is performed, and effects of soil properties and modeling methods on pipe’s response are investigated. To do this task Beam, Beam-Shell Finite Element modeling and a Continuum shell FE models of a 90 degrees elbow are employed. In the Beam model, the pipe is simulated by beam elements while combined shell-beam elements are used for the Continuum shell finite element model. The surrounding soil is simulated by nonlinear spring and solid elements; moreover, soil hardening behavior and soil-pipe slippage are considered in the models. In addition, an equivalent boundary condition has been employed at the end of each elbow leg to simulate far field effects more closely. From these analyses, it can be revealed that axial strain at bends is larger in stiffer soil due to smaller slippage. In addition, a full three dimensional soil-pipe interaction using Continuum Shell FE model causes a substantial increase of elbow strain.

 

Keywords    Buried pipe, Elbow, Finite Element Method, Hybrid model, Continuum model

 

چکیده    در این مقاله، تحلیل لرزه ای ناحیه خم در لوله های مدفون موردنظر است و اثرات مشخصات خاک و روش مدل سازی نیز بر واکنش لرزه ای لوله بررسی خواهد شد. به این منظور سه روش مدل سازی شامل مدل های تیر، تیر-پوسته، و پوسته-محیط پیوسته از یک خم 90 درجه مورد بحث قرار می گیرد. در مدل تیر، لوله توسط المانهای تیر جزء بندی می شود در حالیکه از ترکیبی از المانهای تیر و پوسته در روش دوم و از المانهای پوسته در یک محیط سه بعدی در روش سوم استفاده می گردد. خاک اطراف در دو روش اول به وسیله فنرهای غیرخطی با قابلیت مدل سازی لغزش بین لوله و خاک و در روش سوم با المانهای سه بعدی مدل می گردد. به علاوه، در دو انتهای لوله شرایط مرزی سازگار با طول نامحدود لوله و انتشار امواج تا بی نهایت درنظر گرفته می شود. در نتیجه انجام تحلیل های دینامیکی غیرخطی نتیجه گرفته می شود که کرنش محوری در ناحیه خم در خاکهای سخت بیشتر است که به علت لغزش کمتر بین خاک و لوله می باشد. از سوی دیگر، در تحلیل سه بعدی سیستم لوله-خاک، کرنش های بزرگتری در ناحیه خم به دست می آید.

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