بررسی تجربی و تحلیلی رفتار تیرهای بتن‌آرمه ی تقویت‌شده با تسمه‌های CFRP پیش‌تنیده به روش NSM

نوع مقاله : پژوهشی

نویسندگان

• علی حاجی هاشمی
• داوود مستوفی نژاد
• مجتبی ازهری

دانشگاه صنعتی اصفهان

10.22067/civil.v26i1.44035

چکیده

مقاله‌ی حاضر تحقیقی است در مورد مقاوم‌سازی تیرهای بتنی با استفاده از تسمه‌های CFRP که در شیارهایی که از قبل در پوشش بتنی تیرها ایجاد شده‌اند کار گذاشته می‌شوند. این روش دارای مزایای بسیاری است و در مقایسه با روش چسباندن مصالح FRP روی سطح خارجی اعضای سازه‌ای، امکان انتقال مؤثرتر تنش‌های نرمال و برشی بین مقاوم‌کننده‌ها و سازه را فراهم می‌کند. در این مقاله مزایای این روش از نظر ظرفیت باربری، سرویس‌دهی و استفاده‌ی سطح بالاتر از ظرفیت مصالح FRP در مقایسه با شیوه‌ی معمول چسباندن این مصالح روی سطح اجزای سازه‌ای، از نظر تحلیلی و عملی، مورد بررسی قرار گرفته است. به این منظور پنج عدد تیر بتن مسلح ساده در آزمایشگاه سازه‌ی دانشگاه صنعتی اصفهان مورد آزمایش قرار گرفته‌اند. از این تعداد، یک تیر به‌صورت نمونه‌ی تقویت‌نشده (مبنا)، یک تیر به‌صورت تقویت‌شده‌ی غیر پیش‌تنیده، و سه نمونه‌ی دیگر به‌صورت تقویت شده‌ی پیش‌تنیده تا سطح پنج، بیست و سی درصد کرنش نهایی اسمی تسمه‌های CFRP مورد آزمایش قرار گرفته‌اند. نتایج آزمایش‌ها حاکی از آن است که تیرهای پیش‌تنیده مقادیر بالاتری از بار ترک خوردگی و بار تسلیم را در مقایسه با نمونه‌ی تقویت‌شده‌ی غیر پیش‌تنیده نشان می‌دهند. در این تحقیق بار ترک‌خوردگی در تیرهایی که تا سطح 5، 20 و 30 درصد ظرفیت اسمی مصالح CFRP پیش‌تنیده شده‌اند، به‌ترتیب تا 117، 5/127 و 5/144 درصد بار ترک‌خوردگی در نمونه‌ی مبنا افزایش یافتند. در کنار بار ترک‌خوردگی بالاتر، ترک‌های ایجادشده در نمونه‌های تقویت‌شده‌ی پیش‌تنیده، دارای عرض و توزیع محدودتر بوده‌اند. هم‌چنین تیرهای تقویت‌شده‌ی پیش‌تنیده در مقایسه با نمونه‌ی غیر پیش‌تنیده دارای ظرفیت باربری نهایی بیش‌تری بوده و شکست آن‌ها متناظر با خیزهای کوچک‌تری بوده است؛ به‌طوری که ظرفیت باربری نهایی در تیرهایی که تا سطح 5، 20 و 30 درصد ظرفیت اسمی مصالح CFRP پیش‌تنیده شده‌اند، به‌ترتیب 5/11، 7/14 و 0/15 درصد نسبت به نمونه‌ی مبنا افزایش یافتند.

کلیدواژه‌ها

• بتن مسلح
• مقاوم‌سازی
• مصالح CFRP
• روش NSM
• پیش‌تنیدگی
• خدمت‌پذیری

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عنوان مقاله [English]

Experimental and Analytical Investigation of Behavior of RC Beams Strengthened by Prestressed CFRP Straps using NSM Method

نویسندگان [English]

• Ali Hajihashemi
• Davod Mostofinejad
• mojtaba Azhari

چکیده [English]

The current study is focused on strengthening of reinforced concrete (RC) beams using CFRP straps installed in pre-cut grooves. The method which is referred as near surface mounted (NSM) benefits considerable advantages in comparison with the conventional externally bonded reinforcement (EBR) method and provides better normal and shear stress transfer between the FRP and concrete substrate. The advantages of NSM method compared to EBR are investigated in this paper from viewpoints of loading capacity, serviceability and better use of FRP materials. Five simply-supported RC beams were cast and tested in the laboratory of Department of Civil Engineering of Isfahan University of Technology (IUT). One of the beams was un-strengthened (base specimen) while one was strengthened without prestressing and the other three were strengthened with CFRP straps with prestress up to 5, 20, and 30 percents of the nominal capacity of the composite. The results revealed that the prestressed beams show higher values of cracking and yield loads compared to strengthened specimen without prestressing. The cracking loads for the specimens with 5, 20, and 30 percents prestressing were respectively 117%, 127.5%, and 144.5% higher than that of base specimen; while the cracks in prestressed strengthened specimens were more limited with smaller crack width. Furthermore, the strengthened beams by prestressed CFRP had higher ultimate loading capacities and their failures happened at smaller deflections. The ultimate loads for the specimens strengthened by CFRP prestressed up to 5, 20, and 30 percents of their ultimate capacity were 11.5%, 14.7%, and 15% higher, respectively, compared with that of base specimen.

کلیدواژه‌ها [English]

• RC Beam
• Strengthening
• CFRP Composite
• Prestressing
• NSM Method
• Serviceability

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