مقايسه روش‌هاي مختلف تقويت قاب‌هاي بتن مسلح با استفاده از ورق FRP از نظر عملكرد لرزه‌اي

In engineering construction projects, strengthening existing structures and their components is often necessary due to various reasons such as design flaws and material weaknesses. Among the structural systems that require retrofitting, moment frames are recognized as one of the most common systems resistant to lateral loads and are commonly used in building design. These frame connections are subjected to high stress during earthquakes. The use of fiber-reinforced polymer composites, especially fiber-reinforced polymer (FRP) jackets, has become a popular and effective method for increasing the stiffness and resistance of structures against seismic effects. This thesis investigates and compares common FRP retrofitting methods, including externally bonded reinforcement (EBR), externally bonded reinforcement on grooves (EBROG), and near-surface mounted (NSM) reinforcement applied to the side of the beam-column joint in 3-, 5-, and 7-story moment frame systems. The seismic performance of these frames is eva‎luated through nonlinear pushover and incremental dynamic analyses under various earthquakes. The aim of these analyses is to investigate the improvement in structural performance using these methods. Therefore, a reinforced concrete beam-column specimen strengthened with FRP sheets was validated in the Abaqus software. Subsequently, a concrete frame was validated in the OpenSees software to confirm the analytical model of the beam-column. Additionally, three beam-column specimens were studied in OpenSees to investigate pinching behavior. To analyze and study the frames, their beam-column connections were modeled and analyzed in Abaqus, and then the behavior of these connections was applied and investigated in OpenSees. Subsequently, the aforementioned frames were subjected to nonlinear and incremental dynamic analyses in OpenSees. According to the results of the pushover analysis, the frames reinforced with the EBROG method in the 5- and 7-story frames withstood higher lateral loads compared to other methods, and the NSM method in the 3-, 5-, and 7-story frames exhibited different performance compared to other methods. The results of the dynamic analysis showed that the EBROG and EBR methods had nearly similar performance, but in the 5- and 7-story frames, the NSM method had a weaker performance compared to other methods. The spectral acceleration corresponding to a 50% probability of exceedance in the 3-story frame showed a 13% better performance for the EBR and EBROG methods and a 17% better performance for the NSM method compared to unreinforced frames. In the 5- and 7-story frames, the EBR and EBROG methods had nearly 30% better performance, on average, and the NSM method had a 19% better performance compared to unreinforced frames. The frame reinforced with the NSM method can exhibit different behavior depending on the cross-sectional dimensions. In the 5- and 7-story frames, using a larger number of FRP strips in the height of the beam parallel to the beam can significantly improve the structural behavior compared to the other two methods.

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