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    Enhancement of Flexural Strength Capacity of RC-Beams using LC-GFRP Plates with Effective Debonding Techniques
    (2026-07-01)
    Rodsin, Kittipoom
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    Ngamkam, Kunanon
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    ; ;
    Mehmood, Tahir
    Strengthening of reinforced concrete (RC) beams by externally bonded Carbon Fiber Reinforced Polymer (CFRP) is found to be a very effective method to increase their flexural strength capacity. However, the strengthening cost of the CFRP technique is very high and clients tend to avoid such expensive retrofitting methods. An alternative strengthening material, such as Glass Fiber Reinforced Polymer (GFRP), is a much less expensive material compared to CFRP. The GFRP strengthening method can achieve comparable strength gain and is an effective solution for strengthening RC beams. However, due to the lower strength and stiffness, a larger thickness of GFRP is required to obtain the target tensile strength. This increase in fiber thickness results in the commonly observed debonding failure of the GFRP-plated RC beams. Therefore, this study investigates the end anchoring technique by testing five beams under three-point bending. The first beam served as a controlled beam, while the second and the third beams were strengthened with one and three layers of GFRP to investigate the effect of the number of GFRP layers on debonding behavior. Anchored bolts were used to prevent debonding in the fourth specimen. The innovative W-shape inclined jacket technique was used for the last specimen. The test results revealed that the GFRP could effectively increase the beam's flexural strength. Nevertheless, when a larger number of GFRP layers was used, the debonding of GFRP occurred at an early loading stage. With the anchored bolted technique, the flexural strength of the RC beam was found to increase twice compared to the controlled specimen before failure due to the pulling off of the anchored bolts. Widespread shear cracks were observed near the failure stage. For the W-shape inclined jacket strengthening technique, the flexural strength was increased to a similar order as the anchored bolted technique, but the failure mode was due to slippage of the GFRP against the W-shape inclined jacket. Due to the use of a W-shape inclined jacket, the shear strength of the beam increased significantly. Therefore, the crack patterns near the final stage were controlled by flexure. The test results revealed that both techniques are effective methods to enhance the flexural strength of the GFRP-strengthened beam by achieving a similar magnitude of strength gain but failing in different failure mechanisms.
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    Item type:Publication,
    Collapse prevention of pre-stressed electric transmission poles using glass fiber reinforced polymers
    (2025-07-01) ;
    Rodsin, Kittipoom
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    ;
    Mehmood, Tahir
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    Nawaz, Adnan
    Natural hazards such as strong winds, typhoons, and earthquakes have caused massive economic losses in the form of damage to residential and life-line structures. Electric transmission infrastructures are life-line structures susceptible to severe damage under lateral loads like wind and earthquakes. This study focused on vulnerability assessment and measures to reduce the expected damage to the prestressed electric transmission poles under lateral loads. The Glass Fiber Reinforced Polymer (GFRP) sheet is selected as a strengthening material because the fiber cost is affordable but still has acceptable high tensile strength. A full-scale 12-meter-long prestressed transmission pole was tested under reversed cyclic lateral loading. Furthermore, another specimen strengthened with the GFRP sheet was tested to quantify the effectiveness of this technique. The experimental results show significant improvement in the lateral response behavior of prestressed poles in terms of lateral drift capacity, ductility, and energy dissipation characteristics. The GFRP-strengthened specimen exhibited a significantly enhanced lateral drift capacity (more than 100 %) compared to the control specimen. The performance of GFRP in preventing the collapse of a full-scale transmission pole is proved experimentally in this study. Finally, a numerical model based on the fiber modeling concept was also implemented in the open-source platform OpenSees to simulate the observed hysteretic behavior for strengthened and unstrengthened prestressed electric transmission poles. The application of this strengthening method is shown to be very practical for collapse prevention of existing PC poles both in terms of performance and budget.
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    Item type:Publication,
    Experimental and numerical seismic assessment of non-ductile reinforced concrete (RC) columns strengthened with glass fiber reinforced polymer (GFRP)
    (2022-10-01)
    Rodsin, Kittipoom
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    Mehmood, Tahir
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    Kolozvari, Kristijan
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    Nawaz, Adnan
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    Samiullah, Qazi
    This study presents an experimental and numerical seismic evaluation of non-ductile reinforced concrete (RC) columns strengthened with glass fiber reinforced polymer (GFRP). Three RC column specimens exhibiting three different modes of failure, flexure, flexure-shear, and shear, were strengthened with locally available, inexpensive GFRP sheets and subjected to reversed cyclic loading. The results showed that GFRP sheets not only enhanced the ductility capacity of non-ductile RC columns but also helped to shift the undesirable shear and flexure-shear mode of failure to a more favorable flexural mode. A numerical model based on the multiple-vertical-line-element-model was also proposed and implemented in OpenSees to simulate the experimentally tested specimens. This simple yet robust model was successful in predicting the force–deformation response, including strength degradation of the tested specimens.