بررسی تحلیلی و آزمایشگاهی تیرهای عمیق بتن مسلح دارای گشودگیهای دایروی تقویت شده با ورق های CFRP

نوع مقاله : علمی - پژوهشی

نویسندگان

1 دانشیار، دانشگاه تربیت مدرس، تهران، ایران

2 دانشجوی دکتری، دانشگاه تربیت مدرس، تهران، ایران

چکیده

ایجاد گشودگی در تیرهای عمیق بتنی به منظور عبور تاسیسات مکانیکی و الکترونیکی و دیگر دلایل معماری باعث کاهش ظرفیت باربری این اعضا می شود؛ از جمله روش های مورد استفاده برای جبران این نقص، تقویت این اعضا با ورق های CFRP (Carbon Fiber Reinforced Polymer) است که کارایی بالای آن ها در افزایش مقاومت و شکل پذیری اجزای بتنی در بسیاری از تحقیقات گذشته به اثبات رسیده است. در این پژوهش با انجام آزمایش بارگذاری تک نقطه ای مونوتونیک بر روی 5 عدد تیر عمیق بتن مسلح با ابعاد mm100x500x1200 و دارای یک زوج گشودگی دایروی به قطر 200 میلی متر، به بررسی روش و جهت نصب ورق های تقویتی CFRP و اثر آن ها بر روی رفتار این تیرها پرداخته شده است. روش های مورد بررسی در این تحقیق شامل آماده سازی سطحی EBR (Externally Bonded Reinforcement) و شیارزنی از نوع EBROG (Externally Bonded Reinforcement On Grooves) بوده که به دو صورت دورپیج و مورب مورد استفاده قرار گرفتند. نتایج حاصل از این تحقیق نشان دهنده ی تاثیر گشودگی ها در کاهش حدود 59 درصدی ظرفیت باربری و 66 درصدی جذب انرژی است؛ همچنین در حالی که روش دورپیچی باعث افزایش 27 درصدی ظرفیت باربری نسبت به نمونه بدون تقویت شده است، آرایش مورب این مقدار را تا حدود 43 درصد افزایش داده که از مود گسیختگی نمونه ها می توان به وضوح اثر شیارها در افزایش کارایی کامپوزیت را مشاهده نمود. علاوه بر بررسی آزمایشگاهی، در این تحقیق مدلی تحلیلی بر مبنای مودهای محتلف شکست تیر عمیق ارائه شده است که با استفاده از آن و با دقت مناسبی می توان ظرفیت نهایی تیرهای عمیق را پیش بینی کرد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Shear Strengthening of RC Deep Beams with Circular Openings by Means FRP Composites

نویسندگان [English]

  • Abolfazl Arabzadeh 1
  • Hamid Karimizadeh 2
1 Department of Civil Engineering, Tarbiat Modares University, Tehran, Iran
2 Department of Civil Engineering, Tarbiat Modares University, Tehran, Iran
چکیده [English]

The high depth created favorable space for placing the openings which are to provide some capabilities such as mechanical and electrical installations, but these openings reduced load bearing capacity of the beams. One solution to the mentioned shortcoming is to use FRP-Composite sheets; the effect of FRP-Composites in improving load bearing and ductility of concrete members such as columns and beams is approved in previous investigations. This study utilizes the CFRP sheets to compensate for weakness arisen from the created openings. To this end, 5 deep beams with 10x50x120 cm dimensions, each having two circular openings with 20 cm diameter placed in symmetrical order, are constructed and undergone a three-point monotonic bending. The Externally Bounded Reinforcement (EBR) and Externally Bounded Reinforcement on Grooves (EBROG) methods have been utilized to install the FRP sheets in two configurations being wrapped around and inclined. The results have shown the superiority of EBROG method as well as the efficiency of the inclined orientation of strengthening sheets in increasing the load bearing-capacity. Also, Shear failure was the type of failure in beams and it has been observed that generally, diagonal cracks, which lead to the strut formation, tend to be formed in the beams. The cracks started from the support plates and propagated towards the loading plate. In addition to the extended cracking, the strengthened specimens have experienced debonding and failure in their composite strips. The strengthening strips have experienced failure in the wrapped specimen as a result of providing suitable confinement and leaving no chance for strip debonding as well as in the specimen with inclined strengthening strips as a result of the high efficiency of tensile stresses on the strips. Compared to the related non- strengthened specimens, the load bearing capacity increase arising from inclined orientation is 40% to 43%. In addition, this amount compared to the wrapped around specimen is about 16%.

کلیدواژه‌ها [English]

  • Reinforced concrete deep beams
  • opening
  • CFRP composites
  • EBR method
  • EBROG method
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