مطالعه آزمایشگاهی تیرهای عمیق بتن مسلح تقویت شده برای برش با CFRP به روش NSM

نوع مقاله: علمی - پژوهشی

نویسندگان

1 استادیار، گروه مهندسی عمران، دانشگاه مازندران، بابلسر، ایران

2 مربی، گروه مهندسی عمران، دانشگاه مازندران، بابلسر، ایران

3 کارشناس ارشد مهندسی سازه، گروه مهندسی عمران، دانشگاه مازندران، بابلسر، ایران

چکیده

در این تحقیق، رفتار آزمایشگاهی تیر عمیق بتن مسلح که با ورق پلیمر مسلح شده با الیاف کربنی (CFRP) به دو روش نصب خارجی (EB) و روش نصب در شکاف نزدیک سطح (NSM) مقاوم‌سازی برشی شده، مورد بررسی قرار گرفته است. برای این هدف، 6 تیر به طول 145 سانتی متر، ضخامت 15 سانتی متر و ارتفاع50 سانتی متر ساخته شده و تحت آزمایش قرار گرفتند. آرایش ورق CFRP روی جان همه تیرهای مقاوم‌سازی شده، بصورت قطری و عمود بر خط واصل بین زیر بار تا محل تکیه گاه می باشد. نمونه‌ها به دو گروه با توجه به میزان فولاد مسلح کننده برشی تقسیم می شود؛ هر گروه دارای سه تیر می باشد که تیر اولی تیر کنترل و مقاوم سازی نشده، تیر دوم با روش EB مقاوم سازی شده و تیر سوم با همان مقدار ورق CFRP با روش NSM مقاوم سازی شده است. همه تیرها تا مرحله گسیختگی بارگذاری شده و در حین بارگذاری مقدار کرنش بتن فشاری، کرنش فولاد کششی، عرض ترک و تغییر شکل وسط دهانه تیر اندازه گیری شده است. نتایج آزمایش نشان می دهد که ظرفیت باربری و تغییر شکل نهایی تیرهای مقاوم سازی شده با روش NSM به ترتیب تا 18 درصد و 16 درصد بیشتر از تیر کنترل می باشد. همچنین ظرفیت باربری و تغییر شکل نهایی تیرهای مقاوم سازی شده با روش NSM به ترتیب تا 6 درصد و 15 درصد بیشتر از تیرهای مقاوم‌سازی شده با روش EB می باشد. میزان کرنش فشاری بتن در حالت نهایی در ناحیه خمش ثابت در تیرهای مقاوم‌سازی شده با روش NSM حدود 50 درصد بیشتر از تیرهای مقاوم‌سازی شده با روش EB میباشد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Experimental Investigations of RC Deep Beams Strengthened in Shear using NSM CFRP System

نویسندگان [English]

  • Habib Akbarzadeh Bengar 1
  • Mohsen Ahmadnezhad 2
  • Mehdi Noroozi 3
1 Assistant Professor, Department of Civil Engineering, University of Mazandaran, babolsar, Iran
2 Academic Member, Department of Civil Engineering, University of Mazandaran, babolsar, Iran
3 Structure Engineer, Department of Civil Engineering, University of Mazandaran, babolsar, Iran
چکیده [English]

This paper presents the test results of an experimental study that investigates the behavior of RC deep beams strengthened in shear with externally bonded (EB) and near surface mounted (NSM) techniques using CFRP strip. A total of 6 RC deep beams were constructed and tested under four-point bending. Test specimen had a cross section of 150 × 500 mm and a total length of 1450 mm. This study included two parameters; techniques (NSM and EB) used for strengthening and amount of shear steel reinforcement ratio. All of the strengthened beams have the same CFRP configurations; and CFRP strips were bonded perpendicular to the diagonal connecting the loading and the support points. The specimens were divided into two groups based on the shear steel reinforcement ratio. There were three beams in each group. One of them was a control beam, the rest of the beams in each group were strengthened by EB or NSM techniques. The amount of CFRP strip in EB and NSM techniques is equal. All of the beams were loaded until failure and during the experiment, deflection and compressive strains of concrete, tensile strain of longitudinal steel bar at mid span and crack width of flexural and shear, were measured. The test results showed that shear strengthening of the deep RC beams with NSM technique causes to increase in ultimate load capacity and ultimate deflection capacity by 18% and 16% respectively, compared with the control beam. Also, the ultimate load capacity and ultimate deflection capacity of deep RC beams strengthened with NSM technique are 6% and 15% more than beams strengthened with NSM technique respectively. The concrete compressive strain at ultimate load of deep RC beams strengthened with NSM technique is 50% more than beams strengthened with NSM technique.

کلیدواژه‌ها [English]

  • RC deep beam
  • shear strengthening
  • CFRP
  • EB
  • NSM

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