اصلاح طیف طراحی آئین نامه 2800 ایران برای ساختگاههای نزدیک گسل با استفاده از زلزله های ثبت شده با و بدون اثرات جهت داری ( مقایسه با UBC-97و ASCE-7-2005)

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشیار، دانشکده مهندسی عمران، دانشگاه علم وصنعت ایران

2 دانشجوی دکتری، دانشکده مهندسی عمران، دانشگاه علم وصنعت ایران

چکیده

مناطق پر جمعیت زیادی از ایران را زلزله های حوزه نزدیک با ویژگی جهت داری پیش سوی و جابجائی ماندگارتهدید میکند که میتواند موجب خسارات سنگینی شود. علت عمده آن وجود گسل های فعال اطراف تعدادی از شهر های پر چمعیت ایران است. بعنوان نمونه شهر تهران در محاصره گسل های مشا، ری، کرج، و شمال میباشد.از طزف دیگر، طیف استاندارد 2800که بر اساس احتمال فراگذشت ده در صد در پنجاه سال میباشد، عوامل مهم یاد شده را در بر نمیگیرد.مقصود از این نوشتار پیشنهاد اصلاح طیف های موجود برای در برگیری اثرات حوزه نزدیک به نحوی که بتواند در طراحی ساختمانهای با فاصله کمتر از پانزده کیلو متر از امتداد گسل بکار رود. جدول پیشنهادی برای اصلاح طیف های موجود حاصل ازتحلیل 58 فقره زلزله های واقعی است که در یک روند احتمالاتی با استفاده از سه رابطه کاهندگی مشهور بدست آمده است. نتایج که با متوسط گیری تعداد کافی از ساختگاههای حوزه نزدیک ( 15کیلومتری) محاسبه شده با مقادیر نظیر در آئین نامه های UBC-97 و ASCE-7-2010 برای درک چگونگی تفسیر اختلافات مقایسه شده است. به امید آنکه این گام کوچک بتواند راهگشائی باشد که در آینده طیف های استاندارد ایران قابلیت جوابگوئی دقیقی از مسائل حوزه نزدیک زلزله باشد بطوریکه در صورت رخداد چنین زلزله هائی شاهد کمترین آسیب باشیم.

کلیدواژه‌ها

عنوان مقاله [English]

صلاح طیف طراحی آئین نامه 2800 ایران برای ساختگاههای نزدیک گسل با استفاده از زلزله های ثبت شده با و بدون اثرات جهت

نویسندگان [English]

  • AHMAD NICKNAM 1
  • Ehsan Yousefi Dadras 2
1 Associate Professor, School of Civil Engineering, Iran University of Science and Technology
2 Ph.D. Candidate, School of Civil Engineering, Iran University of Science and Technology
چکیده [English]

Many populated urban areas of Iran are threatened by near source problems; forward directivity effects and fling step, which may cause huge catastrophic. The major reason is that this country is surrounded by the two huge mountain chains, Alborz and Zagross. As an example, Tehran is a city faced around with four near active faults, Mosha, North, Ray, and Karaj faults, which are potentially hazardous. This is under the condition that the design response spectra [A*B(T)] in Iranian Standard No. 2800, which is established on the basis of ten percent chance in fifty years, does not illustratively account for the directivity effects for sites located at near sources. This article is intended to propose a technique to descriptively modify the far field response spectra taking into account such problems for sites 20 Km far away from the active faults. The proposed modification factors are developed based on a limited number of near source data with and without directivity effects (58 recorded data) using three attenuation relationships. The proposed coefficients for four site soil conditions are implemented to the existing far field design response spectra presented in the fourth version of the response spectra. A comparison is made with those of UBC-97 and ASCE-7-2005 corresponding to two seismicity cities in the United State aimed at understanding how to assess their differences. The recommended technique may be interpreted as a start for developing a series of design response spectra having the potentiality of more accurately accounting for the near source problems.

کلیدواژه‌ها [English]

  • Standard No. 2800
  • Near Source Problems
  • Forward Directivity Effects

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