تحلیل هزینه سازه ای در چرخه عمر برای تغییرات ظرفیت خمشی تیرهای بتن آرمه در معرض خوردگی میلگرد

نوع مقاله : علمی - پژوهشی

نویسندگان

1 کارشناسی ارشد، دانشگاه صنعتی نوشیروانی بابل، ایران

2 دانشیار گروه سازه و زلزله دانشکده مهندسی عمران، دانشگاه صنعتی نوشیروانی بابل، ایران

10.22065/jsce.2019.195618.1908

چکیده

شرایط مهاجم محیط های خورنده به علت حمله یون های مخرب سبب خوردگی بیش از حد میلگردهای فولادی مدفون در بتن مسلح می شوند که موجب کاهش سطح مقطع فولاد و زوال مقاومت سازه می گردد. تیرهای بتنی در شرایط خوردگی انواع مختلفی از عدم قطعیت در فازهای خوردگی در طول عمر خدمت پذیری دارند، که بایستی مطابق با یک مدل احتمالاتی مناسب در تحلیل قابلیت اعتماد لحاظ گردند. هرچند که بروز پدیده خوردگی غیر قابل اجتناب می باشد، اما می توان با انتخاب روش های مناسب و نیز بهره گیری از نتایج آنالیز های هزینه چرخه عمر، ضمن به تاخیر انداختن خوردگی، هزینه های تعمیر و نگهداری را نیز به حداقل رساند. در این نوشتار در ابتدا مطالب مرتبط با نحوه مدلسازی خوردگی اعمالی در روش اجزا محدود و نتایج حاصل از تغییرات ظرفیت در میزان درصد خوردگی های متفاوت برای تیرهای طراحی شده از دو روش طراحی حالت حدی و طراحی مقاومت، بررسی می شوند. در ادامه ضمن در نظر گرفتن ظرفیت خمشی به عنوان متغییر تصادفی در محاسبه احتمال کاهش ظرفیت مقاطع خورده شده که از طریق تعریف فرایند گاما صورت می پذیرد، به بررسی و بهینه یابی هزینه های ناشی از خرابی در چرخه عمر خدمت پذیری تیرهای بتن مسلح از طریق فرایند تجدید، پرداخته می شود. نتایج حاکی از آن هستند که حدود مجاز خرابی که تعیین کننده آستانه انجام تعمیرات در تیرهای مدلسازی شده می باشند تاثیر بسزایی در احتمال خرابی دارند به طوری که با افزایش 10% حدود 5 سال برای طراحی حالت حدی و5/3 سال برای روش طراحی مقاومت، احتمال وقوع خرابی افزایش می یابد. مقدار بهینه زمان تعمیرات نیز در حدود مجاز خرابی در تیر طراحی شده از روش طراحی مقاومت کمتر از زمان متناظر در روش طراحی حالت حدی می باشد.

کلیدواژه‌ها


عنوان مقاله [English]

Structural Life-Cycle Cost Analysis for Variations of Flexural Capacity in RC Beams with Corroded Rebars

نویسندگان [English]

  • Fatemeh Aslani 1
  • Mehdi Dehestani 2
1 Graduate Student, Department of Civil Engineering. Babol Noshirvani University of Technology, Babol, Iran
2 Associate Professor, Department of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran
چکیده [English]

This paper presents an approach for evaluating structural resistance degenerate due to reinforcement corrosion and for predicting future structural performance during the service life of the deteriorating reinforced concrete beams due to corrosive environments. a finite element method is adopted for envisioning the nonlinear flexural behavior of intact and corroded RC beams based on Ultimate strength design method and Load and resistance factor design method approaching this aim, the impact of corrosion of embedded reinforcing element on the flexural capacity of corroded reinforced concrete structures is estimated. A stochastic degeneration model based on gamma process is utilized to assess the probability of failure of structural flexural capacity over the lifetime. Optimal repair planning and maintenance strategies throughout the service life are circumscribed by evaluating the cost for maintenance and the risk of structural failure. Based on the conclusions from the numerical model including two RC beams subjected to reinforcement corrosion the following results are drawn: The permissible deterioration limits that describe the thresholds of the deterioration for the safety and repair requirement, held major effects on the probability of failure. The results from the worked example show that the proposed method can afford reliable predictions for structural strength deterioration and efficiently implement a risk-cost-benefit optimized repair procedure through the service life of the structure affected by bar corrosion. The lifetime distribution increases 5years for LRFD method and 3.5 years for USTD method while allowable limits enlargement 10%. The lifetime distribution extends 5years for LRFD method and 3.5 years for USTD method while allowable limits increase 10%.

کلیدواژه‌ها [English]

  • Rebar corrosion
  • life cycle cost
  • reinforced concrete
  • reliability analysis
  • Finite Element
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