روش های تبدیل موجک پیوسته و تحلیل فوریه در ارزیابی خصوصیات تحریک بحرانی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 شهرکرد، بلوار رهبر، کیلومتر ۲ جاده ی سامان، دانشگاه دولتی شهرکرد، دانشکده ی فنی و مهندسی، گروه مهندسی عمران، اتاق 57

2 کارشناس ارشد، دانشکده فنی مهندسی،دانشگاه شهرکرد

3 دانشیار گروه عمران، دانشگاه شهرکرد، شهرکرد

چکیده

در طراحی سازه طراح می‌بایستی سازه را برای بیشینه باری که احتمال می‌رود سازه در طول عمر خود با آن مواجه شود، طراحی کند. در این مقاله با توجه به اطلاعاتی که از زمین لرزه‌های رخداده درگذشته به دست می‌آید، تحریکات بحرانی قاب برشی مجهز شده به مهاربند بازویی، تحت دو حالت قیدی محاسبه می‌شوند. بدین منظور یک مسئله‌ی بهینه سازی غیرخطی حل می شود و در آن تابع هدف بیشینه سازی جابجایی بام سازه در نظر گرفته می‌شود. در هر حالت قیدی تحریکات بحرانی محاسبه و به ترتیب تحت عنوان تحریکات بحرانی اول و دوم شناخته می‌شوند. در حالت قیدی اول انرژی و بیشینه شتاب به عنوان قیود در نظر گرفته می‌شود درحالی‌که در حالت قیدی دوم، قید حد فوقانی طیف فوریه به این قیود اضافه می‌شود. درنهایت خصوصیات تحریکات بحرانی به همراه زلزله‌های استفاده شده جهت تولید تحریکات بحرانی با استفاده از روش تحلیل فوریه و تبدیل موجک پیوسته بررسی می‌شود. نتایج مثال عددی ارائه شده نشان می‌دهد که طیف فوریه‌ی زلزله‌ی بحرانی حالت اول در فرکانسی نزدیک به فرکانس مود اول ارتعاشی سازه 6/68 برابر بیشینه مقدار متناظر در سایر زلزله‌ها است و همین امر منجر به تولید زمین‌لرزهای بحرانی‌تر شده است. همچنین با استفاده از منحنی زمان- فرکانس، ً زمان غالب فرکانس‌ها (زمانی که بیشتر فرکانس‌ها در آن زمان رخ می‌دهند) برای نشان داده می‌شود که تقریبا تمامی زلزله‌ها بیشتر از ده ثانیه است و همچنین مدت زمان حرکت قوی هر زلزله در داخل بازه‌ی زمانی مربوط به زمان غالب فرکانسی همان زلزله قرار دارد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Continuous Wavelet and Fourier Transform Methods for the Evaluation of the Properties of Critical Excitation

نویسندگان [English]

  • Reza Kamgar 1
  • Noorollah Majidi 2
  • Ali Heidari 3
1 Office No. 57, Department of Civil Engineering, Shahrekord University, Shahrekord, Iran.
2 Shahrekord University, Shahrekord, Iran
3 Associate Professor, Department of Civil Engineering, Shahrekord University, Shahrekord, Iran
چکیده [English]

A designer needs to design a structure with the aim of obtaining the maximum possible load expected for the structure during its lifetime. In this paper, considering the information obtained from the earthquakes, the critical earthquakes were computed for a shear frame building equipped with a belt truss system and subjected to two constraint scenarios. For this purpose, a nonlinear optimization problem has been solved in which the objective function was the maximization of the roof displacement. In the first constraint scenario, the computed critical earthquake was known as the first state critical earthquake. In addition, for the second constraint scenario, the earthquake was named as the second state critical earthquake. In the first scenario, the energy, the duration of strong ground motion, and peak ground acceleration were considered as the constraints, while in the second scenario, the upper bound Fourier spectrum was added to these constraints. Finally, the properties of the initial and critical earthquakes were investigated using the Fourier analysis method and continuous wavelet transform. The numerical results showed that the Fourier spectrum of the first critical earthquake was 6.86 times higher than the maximum values for the same parameter in case of other earthquakes at a frequency near the first natural frequency of the structure. Also, using the time-frequency curve, it was shown that duration of the strong ground motion of all earthquake places within the dominant duration of the frequencies of the same earthquake was more than 10 sec.

کلیدواژه‌ها [English]

  • Critical excitation
  • shear frame
  • wavelet transform
  • Fourier frequency
  • optimization

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نشریه مهندسی عمران امیرکبیر
دوره 52، شماره 12
اسفند 1399
صفحه 3125-3144

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