اثر طبقه بندی محیطی و ضوابط تجویزی آیین نامه بر گسترش عرض ترک ناشی از خوردگی میلگرد

نوع مقاله : علمی - پژوهشی

نویسنده

استادیار،دانشکده صنعت و معدن، دانشگاه یاسوج، چرام، ایران

چکیده

آیین نامه‌های طراحی با ارائه ضوابطی مانند حداقل ضخامت پوشش بتن روی میلگرد، حداقل مقاومت فشاری مجاز و محدود کردن نسبت آب به سیمان، ضوابط مربوط به دوام را تجویز می‌کنند. این ضوابط در فاز اولیه موجب به تاخیر افتادن اثر عوامل مخرب محیطی می‌شود ولی با آغاز خوردگی میلگرد این ضوابط تجویزی می‌تواند اثرات متفاوتی را در نحوه گسترش عوامل مخرب داشته باشند. یکی از عواقب ناشی از خوردگی میلگردها، ایجاد ترک در پوسته بتن می‌باشد که با افزایش عرض این ترک‌ها در طی دوره گسترش خوردگی، آثار عامل زیان‌آور خارجی بیشتر می‌گردد. در این پژوهش با استفاده از مهمترین مدل‌های تجربی موجود برای پیش‌بینی عرض ترک، به بررسی اثر تدابیر تجویزی آیین نامه بر مقادیر عرض ترک پرداخته شده است. بدین منظور، ضوابط تجویزی آیین نامه با توجه به وضعیت محیطی سازه بتن مسلح به عنوان شرایط اولیه سازه در نظر گرفته شده است. مدل‌های مورد بررسی بر مبنای خوردگی ایجاد شده بر اثر نفوذ یون کلر انتخاب شده‌اند. مهمترین پارامترهای تاثیر گذار در مد‌‌‌ل‌ها به صورت متغیر تصادفی در نظر گرفته شده‌اند و مقدار عرض ترک به صورت یک متغیر تصادفی بر اساس مدل‌های موجود بدست آمده است. تاثیر انتخاب قطر میلگرد در شرایط محیطی تعریف شده در آیین نامه بر عرض ترک محاسبه شده است. محاسبات عرض ترک با استفاده از روش نمونه‌برداری مونت کارلو انجام گرفته و میانگین مدل‌های تجربی به همراه ضریب تغییرات آن با در نظر گرفتن همبستگی بین مدل‌ها انجام گرفته است. نتایج نشان داده است که استفاده از میلگردهای با قطر کمتر موجب کاهش عرض ترک تا 90 درصد می‌شود. همچنین در صورت آغاز خوردگی میلگرد، در یک زمان معین، سطح ایمنی یک سازه مشخص در شرایط محیطی مختلف به دلیل تفاوت زیاد عرض ترک در آنها همسان نیست.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

The effect of environmental classification and prescriptive requirements of concrete code on the expansion of crack width caused by rebar corrosion

نویسنده [English]

  • Seyed Abbas Hosseini
Assistant Professor, Faculty of Technology and mining, Yasouj University, Choram, Iran
چکیده [English]

The design codes prescribe the durability criteria by providing criteria such as the minimum thickness of the concrete clear cover, and the minimum permissible compressive strength. In the initial phase, these rules delay the effect of destructive factors, but with the initiation of rebar corrosion, these prescribed rules can have different effects on the propagation of destructive factors. One of the consequences of the rebar's corrosion is the creation of cracks in the concrete cover. Whit increasing the width of the cracks during the propagation of corrosion, the effects of external aggressive factors increase. In this research, using the most important existing experimental models for predicting crack width, the effect of prescriptive criteria on crack width has been investigated. For this purpose, the prescriptive rules of the concrete design code were considered as the initial condition of the structure according to the environmental condition of the reinforced concrete structure. The investigated models were selected based on chloride-induced corrosion. The important influencing parameters in the models were considered as random variables and the crack width was obtained as a random variable based on the existing models. The impact of rebar diameter selection in the environmental conditions defined in the design code on the crack width has been calculated. The calculation of the crack width was done using the Monte Carlo sampling method and the average of the experimental models and the coefficient of variation were calculated by considering the correlation between the models. The results have shown that the use of rebars with a smaller diameter reduces the crack width by 90%. Also, if the rebar corrosion begins and a certain period of time has passed since its beginning, the safety level of a certain structure is not the same due to the large difference in the width of the cracks.

کلیدواژه‌ها [English]

  • reinforcement corrosion
  • chloride ion
  • crack width
  • reinforcement concrete
  • concrete durability
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