ارزیابی ضریب بزرگ‌نمایی تغییر مکان در قاب‌های خمشی فولادی ویژه دارای طبقه نرم

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشکده مهندسی عمران، واحد قزوین، دانشگاه آزاد اسلامی، قزوین، ایران

چکیده

یکی از متداول‌ترین نامنظمی‏ های موجود در سازه‏ ها، نامنظمی در ارتفاع و از نوع سختی جانبی می ‏باشد. با توجه به متفاوت بودن پاسخ لرزه‌ای این نوع سازه‌ها نسبت به سازه‌های منظم، ارزیابی و بررسی پاسخ لرزه‌ای سازه‌های نامنظم همواره موضوع تحقیقات بسیاری بوده است. سازه‏ هایی که بر اساس برش پایه تعیین شده توسط آیین ‏نامه طراحی می ‏شوند، تحت اثر زلزله طرح وارد محدوده رفتار غیرخطی می‏ شوند. برای تخمین تغییر مکان واقعی سازه‌ها تحت اثر زلزله طرح، تغییر مکان به دست آمده از تحلیل الاستیک، در سطح برش پایه کاهش یافته، با استفاده از ضریب بزرگ‌نمایی تغییر مکان (Cd) افزایش می‌یابد. تحقیقات مختلف نشان می‌دهند که مقدار Cd تعیین شده توسط آیین ‏نامه ‏ها، مقادیر تغییر مکان‏های جانبی سازه‏ ها را در مواردی با دقت کمتری از واقعیت پیش‏ بینی می ‏کند. هدف اصلی این پژوهش تعیین دقیق‌تر ضریب بزرگ‌نمایی تغییر مکان برای پیش‌بینی حداکثر دریفت بین طبقه‌ای و حداکثر دریفت بام در قاب های کوتاه و میان‏ مرتبه خمشی فولادی ویژه دارای طبقه نرم می‌باشد. تعداد طبقات و محل قرارگیری طبقه‌ی نرم متغیرهای در نظر گرفته شده در این پژوهش می‌باشند. نتایج نشان می‌دهند که استفاده از مقدار Cd = 5.5 که توسط استاندارد 2800 و آیین‌نامه ASCE 7-16 برای سازه‌های فولادی دارای سیستم باربر قاب خمشی ویژه تعیین شده است، در بیشتر طبقات سازه‌های مورد نظر، حداکثر دریفت بین طبقه‌ای و دریفت بام را دست پایین تخمین می‌زند. بنابراین، برای تخمین دقیق‌تر حداکثر دریفت بین طبقه‌ای در سازه‌های مورد نظر تحت اثر زلزله طرح مقدار Cd = 8.5، و برای تخمین دقیق‌تر حداکثر دریفت بام، ضریب بزرگ‌نمایی تغییر مکان (Cd Roof) برابر با 8 پیشنهاد می‌شود.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigation on Deflection Amplification Factor for Special Moment Resisting Frames with Soft Story

نویسندگان [English]

  • Mohammad Amin Mirza Alian
  • Masood Yakhchalian
Department of Civil Engineering, Qazvin Branch, Islamic Azad University, Qazvin, Iran
چکیده [English]

One of the most common irregularities in structures is the irregularity in height and lateral stiffness. Due to the commonness of the use of irregular structures and also the different seismic responses of this type of structures, in comparison with regular structures, investigating the seismic response of irregular structures has always been the subject of several research studies. The structures designed for the reduced base shear, under the design earthquake, have inelastic response. To calculate the real (inelastic) displacements of structures under the design earthquake, the displacements obtained from the reduced base shear, are amplified by the deflection amplification factor (Cd). Seismic codes have dedicated a Cd for each structural system. But different studies have shown that the dedicated Cd by the codes cannot accurately estimate the real displacements. The main purpose of this research is to propose the Cd values for more accurately estimating the maximum inter-story drift ratio (MIDR) and maximum roof drift ratio (MRDR) in steel special moment resisting frames (SMRFs) with the soft story. The number of stories and the location of the soft story are the variables considered in this research. The results show that the use of Cd = 5.5, recommended by the 2800 standard and ASCE 7-16 for steel SMRFs, underestimates the real MIDR and also MRDR, under the design earthquake. It is shown that by increasing the number of stories, the mean Cd obtained from the analyses increases. The reason for this issue is the P-Δ effects that increase by increasing the number of stories. In addition, it is shown that a specified trend cannot be found between the location of the soft story and the mean Cd values in the stories of the structures. Thus, for more accurately estimating MIDR in the considered structures, under the design earthquake, Cd = 8.5 is proposed. Furthermore, for more accurately estimating MRDR, Cd roof = 8.0 is proposed.

کلیدواژه‌ها [English]

  • Displacement amplification factor
  • Steel special moment resisting frame
  • Soft story
  • Inter-story drift ratio
  • Roof drift ratio
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