تأثیر تغییرات طولی ساختار خاک در رفتار لرزه ای لوله های مدفون

نوع مقاله : علمی - پژوهشی

نویسندگان

1 دانشگاه شهید بهشتی

2 استادیار ، دانشکده مهندسی عمران، آب و محیط زیست، دانشگاه شهید بهشتی ، تهران، ایران

3 استادیار، دانشکده مهندسی عمران، آب و محیط زیست، دانشگاه شهید بهشتی، تهران، ایران

چکیده

چکیده: هدف از این مقاله بررسی رفتار خطوط لوله پیوسته گذر کننده از دو خاک با جنس و سختی متفاوت تحت اثر تغییر مکان های زمانی یک زلزله یکسان می باشد. شاخص های تنش و جابجایی به ازای زاویه های مختلف بین خط لوله و مرز بین دو لایه ی خاک بررسی شده است. بدین منظور از نرم افزار آباکوس استفاده گردید و لوله با المان پوسته ای و خاک اطراف آن به صورت توده پیوسته مدل سازی شد. مقدار تنش و جابجایی در طول تقاطع و به ازای زاویه ها ی تقاطع مختلف خاک و لوله و نسبت مدول یانگ متفاوت خاک ها به دست آورده شد. نتایج نشان می دهند که بیش ترین تنش در طول لوله در گره به فاصله مشخصی قبل از مرز و در خاک سخت تر ایجاد می شود. هم چنین با افزایش زاویه تقاطع لوله با مرز بین دو لایه، مقدار جابجایی بیشتر شده و مقدار تنش تا زاویه 30 درجه افزایش و سپس کاهش می یابد. کاهش نسبت مدول یانگ نیز باعث افزایش تنش در قبل و بعد از محل تقاطع می گردد. با تغییر ضخامت لوله، جابجایی و تنش در لوله و خاک لایه ای اطراف آن دستخوش تغییرات قابل ملاحظه ای می گردد به‌طوری‌که با کاهش ضخامت لوله از 20 به 15 میلی متر (کاهش 33%) تنش حدوداً 15 درصد افزایش می یابد. شرایط خاک نرم (خاک دو لایه با جنس خاک نرم) در هر شرایطی منجر به افزایش ظرفیت تغییر شکل و پاسخ لوله می گردد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Soil longitudinal variation effects on seismic behavior of buried pipelines

نویسندگان [English]

  • Farnaz Fadaei 1
  • Nemat Hassani 2
  • Hamid Saffari 3
1 کارشناس ارشد
2 assistant professor,Faculty of Civil, Water and Enviromental Engineering, Shahid Beheshti University, Tehran, Iran.
3 Assistant Professor, Faculty of Civil & Environmental Engineering, Shahid Beheshti University, Tehran, Iran
چکیده [English]

The purpose of this study is to investigate the behavior of continuous pipeline passing through two different layers of soil with different levels of resistance under displacement time-histories of the same earthquake. The values of stress and displacement are studied for different angles between pipe and interface of soil layers. To this end, pipe and the surrounding soil are modeled using shell and solid elements, respectively, in ABAQUS Software. Stress and displacement values are calculated along the intersection and for different values of intersection angle between soil layer and pipeline and different values of Young's modulus of the soils. These evaluations indicate that, the maximum stress along the pipeline occurs at the node in certain distance before the interface in the harder soil. Moreover, with increasing the angle, the resulting displacement increases, and the value of stress increases with angles up to 30˚, beyond which angle it decreases. Also, a decrease in the ratio of Young's modulus increases the stress both before and after the interface. Significant changes are observed in displacement and stress along the pipeline with changing the pipe thickness, so that a decrease in the pipe thickness in the studied model from 20 to 15 mm (33% reduction) results in some 15% increase in the stress. Soft soil (two-layered soft soil) increases pipe displacement and response capacity in every condition.

کلیدواژه‌ها [English]

  • Buried pipeline
  • Earthquake
  • Displacement time-history record
  • Pipeline intersection
  • Finite element method
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