ارزیابی ضریب اصلاح طیفی برای طراحی سازه‌های قاب خمشی فولادی در حوزه‌ی نزدیک به گسل

نوع مقاله: علمی - پژوهشی

نویسندگان

1 استادیار، دانشکده‌ مهندسی عمران، دانشگاه سمنان، سمنان، ایران

2 دانشیار، دانشکده مهندسی عمران، دانشگاه سمنان، سمنان، ایران

3 دانشجوی دکترای مهندسی عمران، دانشکده مهندسی عمران، دانشگاه سمنان، سمنان، ایران

چکیده

استاندارد 2800 ایران برای لحاظ آثار مخرب زلزله‌های نزدیک به گسل در طراحی سازه‌ها، مقادیر طیف طراحی را با استفاده از ضریب اصلاح طیفی (N) که وابسته به پریود ارتعاش سازه و درجه‌ی لرزه‌خیزی منطقه می‌باشد، افزایش می‌دهد. در این مقاله، ضمن بررسی دقت رابطه‌ی ارائه شده در استاندارد 2800 برای تخمین ضریب اصلاح طیفی، برآوردهایی برای این ضریب جهت لحاظ آثار مخرب زلزله‌های نزدیک به گسل بر پاسخ غیر‌ارتجاعی سازه‌های قاب خمشی فولادی ارائه گردیده است. برای این منظور طیف پاسخ رکوردها و نیز پاسخ لرزه‌ای سازه‌های نمونه در شدت‌های طیفی یکسان برای یک مجموعه از زلزله‌های دور از گسل و سه مجموعه مختلف از رکوردهای نزدیک به گسل با یکدیگر مقایسه شده‌اند. برای تعیین پاسخ لرزه‌ای سازه‌های نمونه (شامل پنج قاب خمشی فولادی 3 تا 15 طبقه) در شدت‌های لرزه‌ای مختلف، از نتایج تحلیل‌های دینامیکی افزایشی استفاده شده است. نتایج به دست آمده از این تحقیق نشان می‌دهد که ضریب اصلاح ارائه شده توسط استاندارد 2800 نمی‌تواند به طور کامل آثار زلزله‌های نزدیک به گسل بر پاسخ غیر‌خطی سازه‌های قاب خمشی را پوشش دهد. این موضوع برای سازه‌های کوتاه‌تر آشکارتر است. همچنین نتایج تحلیل‌ها نشان می‌دهد که رابطه‌ی منظمی بین دوره‌ی تناوب اصلی ارتعاش سازه و مقدار ضریب اصلاح طیفی وجود ندارد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Assessment of Spectrum Modification Factor for Design of Steel Moment Frames in Near Fault Regions

نویسندگان [English]

  • Reza Vahdani 1
  • Mohsen Gerami 2
  • Morteza Razi 3
1 Assistant Professor, Civil Engineering Department, Semnan University, Semnan, Iran
2 Associate Professor, Faculty of Civil Engineering, Semnan University, Semnan, Iran
3 PhD Student, Civil Engineering Department, Semnan University, Semnan, Iran
چکیده [English]

Iranian Seismic design code (standard No. 2800) increases the design spectrum ordinates by a modification factor (N factor), to consider the damaging effects of near fault ground motions in design procedure of structures. Accordingly, the spectrum modification factor depends on fundamental period of vibration and seismicity level of the region. In this paper, the preciseness of the expression given by Iranian seismic design code for calculation of spectrum modification factor is examined and estimations are suggested for N factor by evaluating the near fault effects on inelastic seismic response of steel moment-resisting frames. For this purpose, the response spectrum shape and nonlinear seismic response of sample structures are evaluated for one set of far fault and three different sets of near fault ground motions. Incremental dynamic analysis is utilized to obtain the seismic response of the sample frames (including five steel frames with 3 to 15 stories) in various intensity levels. The results of the study demonstrate that modification factors provided by standard No. 2800 does not precisely take account the effects of near fault excitations on inelastic seismic response of steel moment-resisting frame structures. Also, it was found that there is no meaningful relationship between spectrum modification factor and structural period.

کلیدواژه‌ها [English]

  • Design spectrum modification
  • Near fault ground motions
  • Steel moment frame
  • Incremental Dynamic Analysis
  • Iranian seismic design code

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