در نظرگیری اثر چشمه اتصال در برآورد دقیق تغییر مکان لرزه ای طبقه در قاب های فولادی خمشی متوسط

نوع مقاله : Articles

نویسندگان

1 دانشگاه علم و فرهنگ

2 پژوهشگاه بین‌المللی زلزله شناسی و مهندسی زلزله

چکیده

در آیین­نامه­های طراحی لرزه­ای، بیشینه تغییرمکان نسبی واقعی ناشی از رفتار غیر الاستیک سازه، از حاصل­ضرب تغییرمکان نسبی حاصل از تحلیل الاستیک خطی در ضریب افزایش تغییر مکان(Cd)  برآورد می‌شود. این ضریب با در نظرگیری تغییر مکان‌های غیرخطی اعضای سازه به­دست آمده و مقدار آن تابع نوع سیستم سازه­ای می‌باشد. اثر چشمه اتصال، یکی از عوامل مؤثر در افزایش تغییر مکان­ جانبی طبقات می‌باشد ولی این عامل در برآورد مقدار ضریب Cd لحاظ نشده است. هدف اصلی این مطالعه، درنظرگیری اثر چشمه اتصال در این ضریب برای ساختمان­های دارای قاب خمشی فولادی متوسط می‌باشد. به این منظور، یک ساختمان چهار طبقه، یک‌بار با مقطع I شکل و یک‌بار با مقطع قوطی طراحی شده است. قاب­های خمشی مورد نظر تحت تأثیر 46 رکورد با خصوصیات لرزه­ای متفاوت قرار گرفته و از روش دینامیکی غیرخطی برای تحلیل استفاده شده است. نتیجه این مطالعه نشان می­دهد که صرف‌نظر کردن از اثر چشمه اتصال در سازه با مقطع I شکل و قوطی، باعث می‌شود جابه‌جایی طبقات به‌ترتیب 28 و 16 درصد کمتر از واقع تخمین زده شود. بنابراین بر اساس فرضیات و نتایج حاصل از این تحقیق، باید ضریب Cd موجود در آیین‌نامه‌ها را برای قاب­های خمشی متوسط فولادی دارای این­گونه مقاطع به همین میزان افزایش داد.

کلیدواژه‌ها


عنوان مقاله [English]

Accurately Estimaion of Story Drifts of Stell Medium moment Frame Buldings, Considering Panel Zone Effects

نویسندگان [English]

  • Ziba Darabi 1
  • Majid Mohammadi 2
1 University of Science and Culture, Tehran, Iran
2 IIEES, Tehran, Iran
چکیده [English]

In seismic design codes, the maximum real relative displacement due to nonlinear behavior of the structure is estimated from variation coefficient of the relative linear displacement multiplied by the coefficient of deflection amplification factor (Cd). This coefficient is obtained by considering nonlinear displacement of the members of the structure and depends on the lateral load-resisting system. The previous studies indicate that the panel zone can have a significant effect on the behavior of a frame, and in particular, its lateral displacement. Therefore, to predict the precise behavior of the frame, the effect of the panel zone should be considered, but this factor has not been included in the estimation of the Cd value so far. Therefore, the storey drifts are under-estimated. The main purpose of this study is to consider the effect of the panel zone on Cd for Intermediate Moment Resisting Steel Frames (IMRSF). In this regard, two buildings have been designed based on the Iranian seismic design codes in ETABS software. A 4-story building is designed twice, once by I-section columns, and the other by box section columns. The structure with IPE sections has an IMRSF and, a Concentric Bracing Frame (CBF) with conventional ductility in two main directions. However, the structure of the box section has an IMRSF in both directions. After designing the structures, a flexural frame was selected from both structures and was modeled in the OpenSees Software for two conditions: with and without modeling panel zones. Incremental Dynamic Analyses (IDA) has been performed for 46 ground motion records.
To determine a correction factor for Cd in order to consider the panel zone effects, the ratio of the nonlinear maximum drift that of the model without panel zone effects is calculated for each ground motion. The results of the analyses show that in general, considering the effect of the panel zone in the analytical model, leads to an increase in the maximum drift values and ignoring the effect of the panel zone in the structure with the I or Box sections, causes the displacement of the floors to be 28% and 16% less than actually estimated, respectively. This effect for the structure with IPE sections is greater than Box sections, for its smaller web thickness and thus lower thickness of the panel zone. Therefore, it can be concluded that the thickness of the panel zone plays a key role in the structural response. Finally, it is recommended to increase Cd coefficient of intermediate moment resisting frames as 1.28 and 1.16 for the structures with I-section and Box-sections in their columns, respectively.

کلیدواژه‌ها [English]

  • Deflection Amplification Factor
  • Panel Zone
  • Nonlinear Time History Analysis
  • Steel structures
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