بررسی شاخص قابلیت اطمینان لرزه‌ای در تونل‌های کم عمق زیرزمینی با ترکیب سه روش سطح پاسخ، هاسوفر- لیند و المان محدود

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکترای مهندسی عمران -مهندسی زلزله دانشگاه آزاد اسلامی واحد علوم و تحقیقات تهران

2 استادیار گروه مهندسی زلزله، دانشکده فنی و مهندسی، عضو هیئت علمی دانشگاه آزاد اسلامی واحد علوم و تحقیقات تهران

3 استادیار گروه مهندسی زلزله و مدیر پژوهش دانشکده فنی و مهندسی، عضو هیئت علمی دانشگاه آزاد اسلامی واحد علوم وتحقیقات تهران

چکیده

صولا سازه‌های زیرزمینی نظیر تونل‌ها توسط محیط اطراف خود (خاک یا سنگ) مقید شده و به همین دلیل در هنگام زلزله به همراه زمین، همچون جسمی یکپارچه عمل کرده و معمولا تشدیدی در آنها رخ نمی‌دهد. بنابراین، پاسخ لرزه‌ای پوشش تونل توجه ویژه‌ای را می‌طلبد. محدود بودن داده‌های تحقیقاتی و تغییرات فضایی گسترده، توصیف موقعیت زمین‌شناختی آنها را دشوار می‌کند. بنابراین، پارامترهای حاکم بر طراحی آنها بسیار زیاد بوده و تغییرپذیری آن را نیز نمی‌توان نادیده گرفت. یک راه حل برای این مسئله طراحی و تحلیل مبتنی بر قابلیت اطمینان است. در این پژوهش تحلیل مبتنی بر قابلیت اطمینان سیستم پوشش یک تونل کم‌عمق زیرزمینی در خاک ارائه می‌شود. مواردی از قبیل توصیف ارتباط بین پوشش تونل و محیط اطراف، عدم دسترسی به یک فرم بسته تابع عملکردی مورد مطالعه قرارگرفته است. همچنین تحلیل‎ها در دو محیط لرزه‌ای و استاتیکی با درنظرگرفتن متغیرهای تصادفی در مشخصات مصالح خاک انجام شده است. پاسخ لرزه‌ای پوشش تونل برای نیروی محوری، لنگرخمشی و نیروی برشی بررسی می‌شود. در این مقاله با ترکیب روش سطح پاسخ (RSM)، مفهوم قابلیت اطمینان هاسوفر-لیند (HLM) و روش المان محدود (FEM) به بررسی عملکرد پوشش تونل (تحت شرایط استاتیکی و لرزه‌ای) پرداخته شده است. نتایج تحلیل‌ها نشان می‌دهدکه شاخص قابلیت اطمینان برای پاسخ نیروی برشی پوشش تونل تحت رکوردهای زلزله، کمتر از نیروی محوری و لنگرخمشی می‌باشد. همچنین در این پژوهش شاخص قابلیت اطمینان برای تمامی پاسخ‌های ایجادشده(نیروی محوری، لنگرخمشی، نیروی‌برشی و جابجایی) در پوشش تونل تحت سطح لرزه‌ای کمتر از سطح استاتیکی بدست آمده است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigating the seismic reliability index in the shallow underground tunnels by composing three methods of response surface method, Hasofer- Lind and Finite element

نویسنده [English]

  • Mohammad reza Momenzadeh 1
1 M.Sc. in Earthquake Engineering; Department of Earthquake Engineering; Islamic Azad University-Science and Research Tehran Branch
چکیده [English]

Underground tunnels, particularly, have distinct seismic behaviour due to their complete enclosure in soil or rock and their significant length. Therefore, seismic response of tunnel support systems warrant closer attention. The geological settings in which they are placed are often difficult to describe due to limited site investigation data and vast spatial variability. Therefore, the parameters which govern the design are many and their variabilities cannot be ignored. A solution to this issue is reliability based analysis and design. These real conditions of variability can only be addressed through a reliability based design.
 
Introduction
The concepts of reliability has been less considered by the researchers in the engineering analysis and design of tunnels and underground spaces. Laso et. al (1995) studied the reliability in the designing of tunnel lining. Quing Lu et. al (2013) evaluated the reliability of the rock tunnels with respecting to several statuses of rupture mode. The studies conducted on the reliability of tunnels, mostly ignored the seismic design parameters as well as the consideration of reliability in the parameters of the surrounding tunnel soil. 
 
Methodology and Approaches
In this research, response surface method (RSM), the reliability concept of Hasofer-Lind and finite element method (FEM) are composed in order to investigate the reliability of the lining of shallow underground tunnels. For this purpose, an underground tunnel with the height of 5m has been subjected to 7 earthquake records using finite element software ABAQUS. The random variables considered for surface response method are soil dynamic elasticity module, cohesion and internal friction angle of the soil. The reliability index has been approximated for axial force, flexural moment, shear force and displacement of tunnel by conducting trial and error tests on the three mentioned parameters.
 
Results and Conclusions
The results obtained in this research are briefly summarized as follows:

The reliability index value is lower in the tunnel lining under seismic loads for all obtained responses, comparing to those under static loading. In the other words, the reliability of soil and tunnel systems are reduced concerning the random nature and criticality of loading as well as randomness of soil parameters .
The reliability index values are lower for the shear force response of the tunnel lining under Earthquake records, comparing to those of axial force and flexural moment. Consequently, it is recommended to retrofit the whole soil under earthquake loading against shear cracking.

کلیدواژه‌ها [English]

  • reliability index
  • Hasofer- Lind method
  • Finite Element Method
  • random variables
  • performance function
  • response surface method
  • Seismic
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