مقایسه‌ی رکوردهای زلزله به دست آمده از شتاب‌نگار و لرزه نگار و مقایسه‌ی پاسخ سازه تحت اثر آنها

مهدی ایزدی, محمد; محمدی, مجید

مقایسه‌ی رکوردهای زلزله به دست آمده از شتاب‌نگار و لرزه نگار و مقایسه‌ی پاسخ سازه تحت اثر آنها

نوع مقاله : Articles

نویسندگان

¹ دانشگاه آزاد اسلامی واحد علوم و تحقیقات تهران

² پژوهشگاه بین‌المللی زلزله شناسی و مهندسی زلزله

چکیده

در تحلیلهای دینامیکی عموماً شتاب زمین به‌عنوان ورودی به سیستم در نظر گرفته میشود و معادله‌ی حرکت متناسب با شتاب در هر لحظه حل و تلاش اعضا و تغییر مکان نسبی طبقات سازه در هر لحظه محاسبه می‌شود. با توجه به اینکه عموماً لرزه‌نگارها و شتاب‌نگارها به‌طور هم‌زمان در یک نقطه نصب نمی‌شوند در برخی موارد رکوردهای زلزله تنها توسط لرزه‌نگارها ثبت میگردد. اگر نگاشت ثبتشده توسط این دستگاه پس از تصحیح، سرعت واقعی زمین باشد بر اساس اصول دینامیک باید از روی آن بتوان شتاب را با مشتق‌گیری از رکورد سرعت محاسبه و نگاشت‌های لرزه و شتاب را به یکدیگر تبدیل نمود. صحت چنین فرضی در این تحقیق مورد ارزیابی قرار می‌گیرد. به همین منظور پس از زلزله‌ی 27 مرداد 1393 به‌منظور ثبت پس‌لرزه‌ها، یک شتاب‌نگار و یک لرزه‌نگار از یک نوع در منطقه‌ی مورموری استان ایلام و در یک مختصات جغرافیایی نصب گردید. برای بررسی این موضوع، از میان رکوردهای به‌دست‌آمده چهار رکورد انتخاب شده است. در ابتدا هر دو نوع رکورد کالیبره و تصحیح می‌شوند و سپس برخی از ویژگیهای آنها مورد مقایسه قرار میگیرند. نتایج به‌دست‌آمده از مقایسههای صورت گرفته حاکی از آن است که دو نوع رکورد شباهت زیادی دارند و به‌خصوص در تحلیل سازههای با دوره‌ی تناوب کمتر از یک ثانیه استفاده از هرکدام امکانپذیر است. Comparing Accelerograms and Seismograms of Earthquakes and their Effects on StructuresMohammad Mehdi Izadi and Majid MohammadiSeismometers and accelerometers pick up velocity and acceleration of seismic events and have different applications, which are mostly used by seismologists and engineers, respectively. Therefore, they are not regularly installed in the same location. It is believed that acceleration and velocity records can be calculated by each other, regarding that acceleration is the derivative of velocity. However, this belief has not been confirmed yet. For example, calculated acceleration, through the derivative of the seismometer record, has not been validated by comparing with the recorded accelerograms. This paper tries to find an answer for this challenge by having a comparison between the recorded accelerograms and the one calculated from seismometer records. For this, an accelerometer and a seismometer, both from the same factory, were installed in Mormori after the main earthquake of this city on August 18, 2014, to record aftershocks. Four events with considerable accelerations were selected among the events and recorded by these two instruments. All recorded data were corrected, and then the recorded accelerograms are compared with those obtained from differentiating of the corresponding seismograms. Some quantitative parameters, as well as response spectrum and Fourier amplitude spectrum have been used for the comparison. The parameters indicate that there are some ignorable differences between the records; the average of the parameters, Cave, is greater than 9.0 for all records; therefore, there is an excellent fit between the compared records.Response spectrums of the recorded accelerograms and the one obtained by differentiating respective seismograms are almost consistent for Tn<1.0 sec; however, they are different for longer vibrational periods. Therefore, for structures with a natural period of vibration (Tn) less than 1 sec, the required acceleration records for time history analysis can be calculated by differentiating the recorded seismograms. However, for structures with a longer natural period of vibration, accelerograms should be applied, and it is better not to rely on the acceleration record calculated by seismograms.Keywords: Accelerogram; Seismogram; Mormori Earthquake; SDOF Response

کلیدواژه‌ها

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