ارزیابی اثرات مقدار و نحوه‌ی مدلسازی میرایی ذاتی بر پاسخ‌های غیرخطی قاب‌های خمشی فولادی کوتاه مرتبه

نوع مقاله : علمی - پژوهشی

نویسندگان

1 گروه مهندسی عمران، دانشکده فنی و مهندسی، دانشگاه آزاد اسلامی واحد تهران جنوب، تهران، ایران

2 گروه مهندسی عمران, دانشگاه آزاد اسلامی, واحد تهران جنوب, تهران, ایران

3 گروه مهندسی عمران, دانشگاه آزاد اسلامی، واحد علوم و تحقیقات، تهران، ایران

چکیده

تحلیل‌ تاریخچه زمانی غیرخطی به عنوان مناسبترین ابزار برای شناخت رفتار واقعی سازه‌ها تحت اثر تحریکات لرزه‌ای به شمار می‌آید. میزان اعتبار نتایج حاصل از این تحلیل به طرز قابل توجهی به نحوه‌ی مدلسازی، جزئیات و پارامترهای معرفی شده بستگی دارد. یکی از جنبه‌های مهم در مدلسازی دینامیکی، روش معرفی میرایی ذاتی سازه و مقدار نسبت میرایی (ξ) می‌باشد که در سالیان گذشته تحقیقات چندانی راجع به تاثیرات آن‌ها بر پاسخ‌های غیرخطی قاب‌های خمشی فولادی انجام نشده است و استفاده از روش رایلی با نسبت میرایی 5% به عنوان یک روال در بین محققین مرسوم بوده است. در تحقیق حاضر سعی شده تا اثرات مقدار و نحوه‌ی معرفی میرایی ذاتی بر پاسخ‌های غیرخطی قاب‌های خمشی فولادی مورد ارزیابی قرار گیرد. برای این منظور یک سازه 4 طبقه که در سال 2007 بر روی میز لرزه ای آزمایش شده است به عنوان معیار در نظر گرفته شده و در نرم افزار OpenSees شبیه سازی گردیده است. میرایی ذاتی برای این سازه به 3 روش: متناسب با جرم و سختی (فرض رایلی)، متناسب با جرم و متناسب با سختی، با در نظر گرفتن 5 مقدار متفاوت نسبت میرایی ( 0.01, 0.02, 0.03, 0.04, 0.05=ξ) تعریف شده است. پس از انجام تحلیل تاریخچه زمانی غیرخطی برای این مدل ها، پاسخ‌های نرم افزاری و آزمایشگاهی مورد مقایسه قرار گرفته و میزان خطای آن ها استخراج گردیده است. نتایج بیان می‌دارد که کاهش نسبت میرایی منجر به کاهش خطای پاسخ های سازه ای به خصوص برای برش و لنگر واژگونی می شود. استفاده از نسبت میرایی 5% برای تحلیل غیرخطی قاب های خمشی کوتاه مرتبه مناسب نیست و دراکثر موارد منجر به پاسخ های دست پایین می شود. در ضمن مدل های میرایی متناسب با جرم و رایلی دقت بالاتری در مقایسه با میرایی متناسب با سختی دارند و خطای کمتری را نشان می دهند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigation of the effects of value and modeling approach of natural damping on nonlinear responses of low rise moment-resisting steel frames

نویسندگان [English]

  • Saman Rahat Dahmardeh 1
  • Mehrtash Motamedi 2
  • Armin Aziminejad 3
1 Department of Civil Engineering, Islamic Azad University, South Tehran Branch, Tehran, Iran
2 Department of Civil Engineering, Islamic Azad University, South Tehran Branch, Tehran, Iran
3 Department of Civil Engineering, Islamic Azad University, Science and Research Branch, Tehran, Iran
چکیده [English]

Nonlinear time history analysis is recognized as the most appropriate tool for assessing the real behaviour of structures during seismic excitations. Validity rate of obtained results from this analysis significantly depends to the modeling, details and defined parameters. One of the main aspects of dynamic modeling is the consideration of natural viscous damping as well as value of damping ratio (ξ), which during last years evaluating the effects of these factors on nonlinear responses of moment-resisting steel frames has been limited, and Rayleigh damping model with ξ of 5% was used by researchers. Therefore, in this study attempt has been made to examine the impacts of value and modeling approach of natural damping on nonlinear responses of moment-resisting steel frames. For this purpose, a full scale 4 story steel structure which tested on shake table in 2007 has been considered as reference and modeled by OpenSees software. Natural damping has been defined with three methods; Rayleigh damping, mass-proportional damping and stiffness-proportional damping, for five different values of damping ratio (ξ=0.01, 0.02, 0.03, 0.04, 0.05). After conducting the nonlinear time history analyses, difference of obtained structural responses compared to the experimental responses has been investigated, and then errors of them have been extracted. Results indicate that reduce of damping ratio leads to the notable decrease of responses, specially, for story shear and overturning moment. The use of 5% damping ratio for nonlinear dynamic analysis of low rise moment-resisting frames is not appropriate and in most of cases leads to the underestimate and unreal results. Besides, it should be noted that the mass-proportional and Rayleigh damping models have higher accuracy in comparison with stiffness-proportional damping model, and these models show lower error.

کلیدواژه‌ها [English]

  • Natural damping
  • Rayleigh method
  • Moment-resisting steel frame
  • Earthquake
  • Nonlinear time history analysis
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