مقاوم‌سازي برشي تيرهاي بتن مسلح به روش نصب نزديك سطح با استفاده از ميله‌هاي ساخته‌شده ازالياف كربن

Strengthening of Reinforced Concrete Structures Using BMCF Bars

چكيده- مطالعه آزمايشگاهي انجام‌شده، تاثير مقاوم‌سازي برشي تيرهاي بتن مسلح به كمك روش نصب نزديك سطح با استفاده از ميله‌هاي ساخته‌شده از صفحات الياف كربن را ارزيابي مي‌كند. براي ايجاد تاخير در شروع جداشدگي ميله‌ از تير، مهار انتهايي جديدي براي آن‌ها پيشنهاد شده كه آزمايش مي‌شود. در اين مقاله، نتايج آزمايش‌هاي انجام‌شده روي شش عدد تير بتن مسلح دوسر ساده با مقطع مستطيل شكل كه در برش، مقاوم‌سازي شده‌‌است، ارايه مي‌شود. پاسخ نيرو-‌ تغييرمكان همه‌ي نمونه‌ها و تغييرات كرنش در قسمت‌هاي مختلف ارايه خواهد شد. همچنين كاركرد و مدهاي گسيختگي تيرها بررسي خواهد شد. نتايج آزمايش‌ها بيانگر از كارامدي ميله‌ها و مهارهاي پيشنهادي بوده است؛ به‌گونه‌اي‌ كه افزايش ظرفيت باربري نمونه‌هاي مقاوم‌سازي شده روش پيشنهادي، 25 تا 48 درصد نمونه مرجع به دست آمده است و در نتيجه استفاده از مهارهاي انتهايي پيشنهادي، انرژي جذب‌شده به‌وسيله‌ي نمونه‌ها، افزايش چشم‌گيري پيدا كرده است. در انتها، مدل تحليلي Rizzo and De Lorenzis براي برآورد مشاركت سامانه مقاوم‌سازي اين پژوهش ارايه شده است كه در مقايسه با نتايج آزمايشگاهي، تخمين قابل قبولي به دست مي‌دهد.

Abstract: This experimental study is intended to evaluate the effectiveness of a Near Surface Mounted (NSM) technique using bars made of carbon fabrics (BMCF) for strengthening of RC beams. When the amount of NSM reinforcement in strengthening of RC beams is low, the failure is likely to be due to debonding of individual reinforcing rod and in this case improved bond properties as well as proper anchoring of the BMCF rods are likely to delay the failure of the beam. BMCF provide a larger perimeter to cross sectional area ratio with respect to conventional rods for the same amount of fibre used, providing potentially higher bond strength. In addition, the circular shape of BMCF is not only convenient for production but also suitable for NSM strengthening as noted by previous researchers. Another key advantage of introducing the BMCF is that it allows the incorporation of a different anchor system that can be used to improve the performance of NSM BMCF reinforcement for strengthening of RC beams in applications with low strengthening reinforcement percentage. A distinguished benefit of the proposed anchor system is that it only requires the access to the beam sides for installation. This means that the proposed anchorage system can be conveniently applied to beams whose top and/or bottom face is inaccessible. A set of deficient beam specimens were designed. All specimens had the same internal reinforcement arrangements. They were 300 mm wide, 350 mm high and 2050 mm long. One half of each beam was designed to be weak in load bearing as the test span while the other half was designed as the strong span. Only the test span was strengthened in with NSM BMCF. The amount of steel reinforcement in the two sides was designed to ensure that shear failure would occur in the test span. All beams were simply supported at the ends and tested under a concentrated monotonic load applied at the mid-span. Test results presented in this paper have confirmed that the use of BMCF is an effective technique for improving the shear capacity of RC beams. The increase in the shear capacity was between 18 to 55% for beams strengthened with BMCF, compared with the reference beam. The load–deflection response of beams is presented. The capacity of specimens for energy absorption are also presented and discussed in this paper. In order to predict the contribution of NSM-BMCF strengthening method, an analytical study is presented in this paper. The analytical procedure is evaluated by experimental findings. It is concluded that the analytical formulation can reasonably estimates the contribution of NSM-BMCF strengthening reinforcement and as a safe design point of view; it is advisable for engineering application aims.