ارزیابی پارامترهای خوردگی آرماتورها جهت تحلیل احتمالاتی تیرهای بتن مسلح

نوع مقاله : یادداشت پژوهشی

نویسندگان

1 استادیار گروه مهندسی عمران دانشگاه زابل

2 گروه مهندسی عمران، دانشگاه آزاد اسلامی واحد فارسان

3 گروه مهندسی عمران، دانشگاه زابل

چکیده

خوردگی میلگردها در تیرهای بتن یک فرایند پیچیده بوده که موجب کاهش سطح مقطع فولاد و زوال مقاومت سازه می‌گردد. تیرهای بتنی تحت خوردگی انواع مختلفی از عدم قطعیت در فاز خوردگی دارند که بایستی مطابق با یک مدل احتمالاتی در تحلیل قابلیت اعتماد لحاظ گردند. پارامترهای خوردگی مانند زمان شروع خوردگی، مقدار انتشار یونهای مخرب و نرخ خوردگی در خوردگی وابسته به زمان تیرهای بتن آرمه تاثیر گذارند. در این مقاله بر اساس انواع خوردگی کلی و موضعی تحلیل آماری با توجه به رویه حداکثر درست نمایی صورت پذیرفته و بهترین تابع توزیع احتمال پارامترهای خوردگی از میان توابع نرمال، لوگ- نرمال، گامبل، وایبول و گاما با استفاده از آماره مربع کا انتخاب گردیده است. در انتها با توجه به تحلیل آماری انجام شده یک تیر بتن مسلح تحت بار گسترده مطابق با تابع شرایط حدی خمشی بر اساس روش شبیه‌سازی مونت کارلو، تحلیل قابلیت اعتماد گردیده است. در این تیر اثر قطر میلگردها و همچنین دوره زمانی خوردگی کلی و موضعی بررسی شده است. نتایج حاکی از آن هستند که پارامترهای خوردگی از تابع توزیع احتمال لوگ-نرمال پیروی می‌کنند و پوشش آرماتورها نقش بسزایی در میزان کاهش سطح میلگردها دارد. افزایش دوره خوردگی بیشتر از 30 سال و کاهش قطر میلگردها کمتر از 18 میلی­متر موجب افزایش احتمال خرابی تیر بتنی تحت خوردگی می‌گردند.

کلیدواژه‌ها


عنوان مقاله [English]

Evaluating the Corrosion of Steel Reinforcement for Probabilistic Analysis of Concrete Beams

نویسندگان [English]

  • Behrooz Keshtegar 1
  • Arash Modhamedi-Farsani 2
  • Hosein Ali Rahdar 3
1 Dept. civil eng. Uneversity of Zabol
2 Department of Civil Engineering, Islamic Azad University, Branch of Farsan
3 Department of Civil Engineering, University of Zabol
چکیده [English]

The corroded reinforcement bars are the important issue of the concrete permanence due to reduction of the safety factor of the structure against the applied external loads. Corrosion of steel reinforcement has a complex process which due to the reduction in the resistance crass sectional area of the reinforced bars and degradation of concrete structure. Therefore, there are more important that the reinforced concrete structures are evaluated under corrosion at service loads due to an optimum and robust design to achieve a good durability and assessed the time-life service. The reinforced concrete beams are a one of most component that implemented for constructing the reinforced concrete. In the period-times the corrosion, the concrete beams have variety uncertainties such as model uncertainty, load and resistance uncertainty. These uncertainties can be considered using a probabilistic model based on the basis of random variables. The random variables in probabilistic models can be given by several statistical characteristics including probability density functions and their parameters (e.g. mean and standard deviation). The various methods including the first-order reliability method (FORM) and the second-order reliability method (SORM) methods, simulation approach and surrogate-based modeling are used to evaluate the probabilistic model in reliability analysis [1]. The Monte Carlo simulation (MCS) is widely used in reliability analysis due to simplicity and more accurately.

کلیدواژه‌ها [English]

  • Mont Carlo simulation
  • Probabilistic analysis
  • reliability analysis
  • Reinforced concrete
  • Corrosion
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