ارزیابی دقت رابطه پیشنهادی FEMA-356 برای محاسبه نسبت میرائی مؤثر میراگرهای ویسکوز و ویسکو الاستیک

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشکده مهندسی، دانشگاه شیراز، شیراز، ایران

2 دانشگاه شیراز، دانشکده مهندسی، بخش مهندسی راه، ساختمان و محیط زیست

چکیده

به منظور بررسی دقت رابطه پیشنهادی FEMA-356در مقایسه با رابطه تحلیلی محاسبه نسبت میرایی معادل سازه ها با میراگرهای ویسکوز و ویسکو الاستیک، معادله دینامیکی حرکت تحت ارتعاش پایه هارمونیک برای ساختمان های برشی با تعداد طبقات دو تا دوارده برای حالات منظم و نامنظم توزیع جرم در ارتفاع، با استفاده از روش های عددی حل شده است.افزون بر آن، حالت هائی نیز در نظر گرفته شده که میراگرها در طبقات محدودی از ساختمان قرار داده شده و ارزیابی دقت رابطه FEMA-356در این حالات صورت گرفته است. نتایج این تحقیق نشان داده که خطای رابطه FEMA-356در مقایسه با روش تحلیلی در ساختمانهای منظم برای میراگرهای ویسکوز در محدوده یک تا سه درصد و برای میراگرهای ویسکوالاستیک در محدوده یک تا 17درصد، با فرض نسبت سختی میراگر به سختی جانبی طبقه برابر ده درصد، می باشد که با کاهش این نسبت سختی به پنج درصد، خطای میراگرهای ویسکوالاستیک در کمترین حالت، به حدود دو درصد کاهش می یابد. همچنین نشان داده شده که بی نظمی جرمی سازه در ارتفاع برای میراگرهای ویسکوز تاثیر قابل ملاحظه ای بر دقت رابطه ندارد در حالی که برای میراگرهای ویسکوالاستیک موجب افزایش قابل ملاحظه خطا می گردد .

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Evaluating Accuracy of FEMA-356 Proposed Equation for Effective Damping Ratio for Viscous and Visco-elastic Dampers

نویسندگان [English]

  • Mohammad Ebrahim Karbaschi 1
  • S .A. Anvar 2
1 Department if Civil and Environment Engineering, School of Engineering, Shiraz university, Shiraz, Iran
2 Department if Civil and Environment Engineering, School of Engineering, Shiraz university, Shiraz, Iran
چکیده [English]

The use of dampers for retroftting and reducing seismic induced vibrations of structures is rising. Among all types of dampers, viscous and visco-elastic dampers are extensively used for buildings. Adding dampers increases equivalent damping ratio of structure which decreases displacement and member stresses. FEMA-356 has proposed an equation for calculating equivalent damping ratio of shear buildings with added dampers, based on the frst mode of vibration. In the present research, the goal was to study the accuracy of FEMA-356 formula for evaluating equivalent damping ratio with
dampers as compared with the theoretical one. For the latter, the calculation is based on the hysteresis force-displacement response of the dampers. For obtaining hysteresis response, dynamic equation of motion of 2 to 12 stories 2D shear buildings equipped with viscous and visco-elastic dampers subjected to harmonic base excitation were solved. Both regular and mass distributed in height irregular structures with added dampers at all levels were considered. In addition to that, dampers were considered at random stories of the buildings and accuracy of equivalent damping ratios of FEMA-356 were evaluated. This study has shown that for viscous dampers, error of FEMA-356 formula in comparison with theoretical
formula for viscous dampers would be in the range of 1 to 3 percent and for visco-elastic ones in which stiffness ratio of visco-elastic dampers to story shear stiffness is 10 percent, would be in the range of 1 to 17 percent. When the stiffness ratio is decreased to 5 percent, the error would decrease to 2, in the worst case. Also, it has been shown that mass irregularity in the height of the buildings increases the maximum error from 17% to 58% for viscoelastic dampers; no signifcant effect for viscous dampers. Moreover, addition of dampers in random stories of buildings up to six stories would increase error of FEMA-356 formula about 42 and 50 percent, respectively, for viscous and visco-elastic dampers.

کلیدواژه‌ها [English]

  • Viscous damper
  • Visco-elastic damper
  • FEMA-356
  • Harmonic base excitation
  • Equivalent damping ratio

مراجع

 
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نشریه مهندسی عمران امیرکبیر
دوره 50، شماره 2
خرداد و تیر 1397
صفحه 303-314

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