ارزیابی احتمالاتی رفتار لرزه‌ای قاب‌های خمشی بتنی ویژه دارای نامنظمی سختی در ارتفاع بر اساس دستورالعمل FEMAP695

نوع مقاله : Articles

نویسندگان

1 دانشکده مهندسی عمران، دانشگاه سمنان، سمنان

2 دانشگاه سمنان، سمنان

3 پژوهشگاه بین‌المللی زلزله‌شناسی و مهندسی زلزله، تهران

چکیده

عملکرد ضعیف و فروریزش ساختمان­های نامنظم سختی در ارتفاع، در طول زلزله­های گذشته منجر به بروز خسارات مالی و جانی جبران­ناپذیری شده است. از این‌رو ارزیابی دقیق­تر این نوع سازه­ها به‌ویژه در سطح عملکردی فروریزش، حائز اهمیت است. در این مطالعه قاب خمشی بتنی ویژه منظم شش طبقه، به‌عنوان مدل مرجع، مطابق با ضوابط آیین­نامه­های داخلی طراحی شده است. سپس 12 قاب نامنظم سختی در ارتفاع با مقادیر و محل­های وقوع متفاوت در ارتفاع، ساخته شده است. جهت ارزیابی فروریزش، رفتار غیرخطی اعضا به روش پلاستیسیته متمرکز، در نرم‌افزار Opensees مدل‌سازی شده است. عملکرد احتمالاتی لرزه­ای قاب‌های مورد مطالعه، مبتنی بر روش دستورالعمل FEMAP695 مورد مقایسه قرار گرفته است. در این ارزیابی، پارامترهای متداول طراحی از جمله ضریب رفتار، ضریب اضافه مقاومت و شکل­پذیری و نیز نسبت حاشیه ایمنی فروریزش1 و همچنین منحنی‌های شکنندگی بررسی شده است. نتایج نشان داد که وجود نامنظمی باعث کاهش ضریب رفتار و ضریب شکل­پذیری می‌شود. بیشترین کاهش در ضریب رفتار نسبت به قاب منظم، مربوط به مقدار فاکتور نامنظمی 4/0 واقع در طبقه اول می­باشد که در حدود 24 درصد تخمین زده شده است. هنگامی‌که فاکتور نامنظمی برابر با 4/0 و در بخش پایینی سازه قرار گیرد، نسبت حاشیه ایمنی فروریزش اصلاح شده، در حدود 30 درصد نسبت به حالت قاب منظم کاهش و احتمال شکست در این قاب برای یک سطح مشخص از نیاز سازه، نسبت به سایر مدل‌ها، افزایش می­یابد. لازم به ذکر است که تغییرات در نسبت حاشیه ایمنی اصلاح شده و احتمال شکست در مدل‌های با نامنظمی واقع در ارتفاع میانی سازه در مقایسه با سایر حالات کمتر است. وجود نامنظمی سختی2 در ارتفاع بنا بر مقدار فاکتور نامنظمی و محل وقوع نامنظمی، بر عملکرد احتمالاتی لرزه­ای سازه­ها در سطح فروریزش تأثیرگذار می­باشد. بنابراین ضروری است در تعریف محدودیت‌های آیین‌نامه‌ای برای این نوع سازه­ها علاوه بر فاکتور نامنظمی، محل اثر نامنظمی نیز به نحو مقتضی در نظر گرفته شود.

کلیدواژه‌ها


عنوان مقاله [English]

Probabilistic Evaluation of the Seismic Behavior of Reinforced Concrete Structures with Stiffness Irregularity Based on the FEMAP695

نویسندگان [English]

  • Elahesadat Hashemi 1
  • Ali Kheyroddin 2
  • Mohsen Gerami 2
  • Abdoreza S. Moghadam 3
1 Department of Civil Engineering, Semnan University, Semnan, Iran
2 Faculty of Civil Engineering, Semnan University, Semnan, Iran
3 Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
چکیده [English]

The use of aesthetic parameters in the architecture of the building as well as the existence of various applications in different stories of a building will lead to irregularities in the structure. Non-uniform distribution of dynamic characteristic, e.g. mass, stiffness and strength of these structures causes the focus of nonlinear deformation, and consequently, the global or local destruction of the structure during an earthquake. For this reason, many current world-wide codes have provided definitions and limitation for irregular buildings. One common type of irregular structures that is important to investigate its seismic behavior is stiffness irregular structures. ASCE 7-16 defines stiffness irregularity as:
Stiffness-Soft Story Irregularity: Stiffness-soft story irregularity is defined to exist where there is a story in which the lateral stiffness is less than 70% of that in the story above or less than 80% of the average stiffness of the three stories above (ASCE 7-16).
Stiffness-Extreme Soft Story Irregularity: Stiffness-extreme soft story irregularity is defined to exist where there is a story in which the lateral stiffness is less than 60% of that in the story above or less than 70% of the average stiffness of the three stories above (ASCE 7-16).
It should be noted that this definition is based on the irregularity magnitude and the effect of the location of irregularity in height of structures has not been mentioned, which can be expressed as a defect in the definition of the stiffness irregularity. The major previous researches on the seismic response of the structures with vertical irregularity have been deterministic that they generally have aimed to calculate the mean values of peak responses. The seismic behavior of the structure due to available uncertainties is probabilistic rather than deterministic. It should be noted that research on the effect of irregular structures on the seismic capacity of structures is less than the effect of irregular structures on the seismic demand of structures. In order to assess the collapse capacity of irregular structures, the use of a collapse behavior model of the elements with respect to the probabilistic process as well as Incremental Dynamic Analysis (IDA) can be effective. Various methods have been developed to evaluate the probabilistic response of structures.
In this study, the effect of the stiffness irregularity on the probabilistic seismic performance of RC moment resistant frames has been studied according to the FEMAP695 (2009) procedure. To do so, nonlinear static analysis and the Incremental Dynamic Analysis (IDA) are conducted. According to the fragility curves, the collapse capacity of the structure is calculated for each model. The CMR for the models is compared to the acceptance collapse criteria based on the FEMAP695 (2009) guideline.
The obtained results show that the irregular structures have different seismic performance than regular one. The results show that both the level of irregularity and the location of irregularity in height affect the seismic responses
of these structures. It seems that the reconsideration of seismic code requirements for stiffness irregularities needs to be necessary to provide more accurate for structures with stiffness irregularities especially for those with an irregularity in the critical stories.

کلیدواژه‌ها [English]

  • Probabilistic Assessment
  • Special Concrete Moment Frame
  • Stiffness Irregularity
  • Fragility Curve
  • FEMA-P695
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