Abstract    The utilization of unbounded external reinforcing bars is one of the strengthening methods used after loading stage and before failure. The method has been used in different forms to strengthen members of reinforced concrete structures. To investigate the effect of utilization of post-tensioned reinforcing bars in this method of strengthening, a number of reinforced concrete beams was tested. Strengthening was carried out by attaching external bars on both outside faces of the beam in the level of internal flexural tension reinforcement. The behavior of strengthened beams was then studied both by experiment and modeling using ANSYS finite element structural software. In post-tensioning of external reinforcing bars, hydraulic jack was used. The results showed that this method of strengthening has increased the flexural capacity, and decreased the ductility of the beams. It was also shown that the increase in flexural strength caused by the utilization of unbounded external post-tensioned reinforcing bars was in reverse proportion with the percentage of internal flexural tension reinforcement. It was also concluded that the method is very effective for beams with lower percentages of internal flexural tension reinforcement.

Keywords    Strengthening, Reinforced concrete beam, Post-tensioning, External reinforcing bar, Nonlinear finite element analysis, ANSYS

چکیده    استفاده از آرماتورهاي خارجي يکي از روش‎هاي مقاوم‎سازي در مرحله بعد از بارگذاري و قبل از شکست مي‎باشد که تاکنون به طرق مختلف کار مقاوم‎سازي با استفاده از آرماتورهاي خارجي صورت گرفته است. به منظور بررسي تاثير استفاده از آرماتور خارجي پس‌کشيده در اين روش مقاوم‌سازي‌، تعدادي تير بتن‎آرمه مورد بررسي قرار گرفتند. مقاوم‎سازي توسط نصب آرماتور خارجي در طرفين تير در ترازي برابر با آرماتور کششي صورت گرفته است. بررسي در دو فاز آزمايشگاهي و مدل‌سازي به وسيله نرم‌افزار صورت گرفته است. که در بررسي آزمايشگاهي، براي ايجاد پس‌کشيدگي در آرماتور خارجي از جک هيدروليکي استفاده شده است. نتايج نشان مي‎دهد که‎اين روش مقاوم‎سازي باعث افزايش ظرفيت خمشي و کاهش شکل‌پذيري مي‎شود و افزايش مقاومت خمشي در اثر استفاده از آرماتور غيرچسبيده پس‌کشيده خارجي با درصد فولاد کششي نسبت معکوس دارد و براي تيرهايي که درصد فولاد کششي کمي دارند، روش بسيار موثري مي‌باشد.

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