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ارزیابی سازه های فولادی دارای سیستم دوگانه ی قاب خمشی و مهاربندی همگرا تحت تاثیر تکرار زلزله‌ها
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نویسنده
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جهان نوروز ,حیدری تفرشی امیر مهدی ,گرامی محسن
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منبع
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مهندسي عمران شريف - 1399 - دوره : 36-2 - شماره : 4/2 - صفحه:121 -132
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چکیده
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رخداد پس‌لرزه در ساختمان‌هایی که در زلزله‌ی اصلی خسارت دیده‌اند، می‌تواند موجب خرابی فزاینده شود. در حالی‌که آیین‌نامه‌های طراحی لرزه‌یی، فقط بر اساس «زلزله‌ی طرح» روند طراحی را ارائه می‌کنند و تاثیرات پس‌لرزه بر طراحی را در نظر نمی‌گیرند. در این تحقیق به‌منظور ارزیابی سازه‌های مورد نظر، شش سازه با سه، پنج، هفت، ده، پانزده و بیست طبقه بر اساس آیین‌نامه‌ی ایران طراحی شده و با استفاده از نرم‌افزار rmperform 3d تحلیل دینامیکی تاریخچه‌ی زمانی بر روی آن‌ها صورت گرفته است. منحنی‌های شکنندگی سازه‌های مورد بررسی در سطوح عملکرد مختلف ترسیم شده‌اند و آسیب‌پذیری لرزه‌یی سازه‌ها بررسی شده است. نتایج نشان می‌دهند که به‌طور میانگین با اعمال زلزله‌ی دوم آسیب‌پذیری سازه‌ها تحت زلزله‌های نزدیک و یا دور از گسل در سناریوی با زلزله‌ی اول به شدت 0/6,g در سطح عملکرد (ls) به‌ترتیب15٪ و 10٪ نسبت زلزله‌ی تک را افزایش داده است. همچنین سازه‌ها در سطح عملکرد (ls)، که موردنظر آیین‌نامه‌های طراحی است، در زلزله و توالی‌های نزدیک گسل مورد نظر عملکرد خوبی داشته‌اند و طراحی بر اساس آن‌ها قابل اعتماد است.
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کلیدواژه
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قاب‌های مهاربندی شده‌ی همگرا، زلزله‌ی حوزه‌ی نزدیک و دور از گسل، توالی لرزه‌یی، آسیب‌پذیری لرزه‌یی، تحلیل دینامیکی غیرخطی، منحنی شکنندگی
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آدرس
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دانشگاه سمنان, دانشکده ی مهندسی عمران, ایران, دانشگاه سمنان, دانشکده ی مهندسی عمران, ایران, دانشگاه سمنان, دانشکده ی مهندسی عمران, ایران
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پست الکترونیکی
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mgerami@semnan.ac.ir
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ASSESSMENT OF STEEL STRUCTURES WITH A DUAL SYSTEM OF MOMENT FRAME WITH CONCENTRICALLY BRACE INFLUENCING REPEATED EARTHQUAKES
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Authors
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Jahan N. ,Heydari Tafreshi A.M. ,Gerami M.
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Abstract
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In the seismic active zones, structures are likely to be subject to multiple earthquakes due to the complex stress interactions among the tectonic plates. A large earthquake is usually followed by numerous aftershocks within a short period. Although aftershocks are normally smaller in magnitude, their ground motion intensities are often large and have different energy contents, compared to the mainshock. These aftershocks have a strong potential to cause additional cumulative damages to structures that have been already damaged by the mainshock and threaten life safety even when only minor damage has remained from the mainshock. Seismic design codes provide a design process based on a design earthquake and do not take into account the effects of the aftershocks on this design. In the present study, by investigating the effect of seismic sequences on structures with different lateral resisting systems, the existing gap within the design guidelines and codes can be filled. In this regard, the performance of steel structures consisting of dual momentresisting frames and concentrically braced systems was investigated in the seismic sequence. To this end, different types of steel structures with 3, 5, 7, 10, 15, and 20 stories were designed and analyzed based on Iranian codes with and without seismic sequences using Perform3D software. The fragility curves from nonlinear analysis at different performance levels under FEMA356 were obtained and the seismic vulnerabilities were evaluated. The results showed that the effect of earthquakes on higher structures was attenuated as a result of a decrease in the magnitude of the earthquake spectrum within longer periods, leading to a reduction in vulnerabilities. Moreover, the structures performed well at the performance level of Life Safety (LS), intended by the design codes; therefore, designs produced based on such levels in the earthquakes and seismic sequences nearfield were assumed to be reliable. According to the results presented in this study, the second earthquake, whose PGA is more than the first earthquake, affects the structural response in the seismic sequence. The probability of the exceedance damage at the performance level (IO) in the farfield earthquakes and seismic sequences is more than that of the nearfield earthquakes, while the probability of exceedance damage at the performance levels (LS) and (CP) in 10, 15, and 20story structures in the nearfield earthquakes and seismic sequences is higher than that of farfield earthquakes. On average, by applying the second earthquake to the first earthquake scenario with the intensity of 0.6g, the vulnerability of structures under nearfault and farfault repeated earthquakes caused an increase in the singleearthquake ratio by 15% and 20% at the performance level of (LS), respectively.
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Keywords
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