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Abstract
The reinforcement of steel beams using prestressed CFRP (Carbon Fiber Reinforced Polymer) plates has become an increasingly popular technique in the retrofitting of existing structures. This paper presents the experimental investigation of the anchorage system used in prestressed CFRP plate reinforcement of steel beams. A series of tests including static, fatigue and long-term creep tests were conducted to evaluate the performance of the anchorage system. The results showed that the anchor system was effective in transferring the prestressing force to the steel beam, providing good bonding between the CFRP plate and the steel beam, and preventing premature failure of the system.
Introduction
The strengthening of existing structures has become a growing concern due to their aging and the need to enhance their safety and durability. CFRP materials have been widely used for this purpose due to their excellent mechanical properties, including high strength-to-weight ratio and corrosion resistance. The use of prestressed CFRP plates has been found to achieve further improvement in the performance of the strengthened steel beams.
Prestressed CFRP plates involve the application of precompression to the CFRP plates before bonding them to the steel beams, thereby enhancing their stiffness and load-carrying capacity. Effective transfer of the prestressing force to the steel beam is essential for the success of the retrofitting process. The anchorage system used to provide good bonding between the CFRP plate and the steel beam is critical to the effectiveness of the entire system.
In this paper, an experimental study was conducted to evaluate the performance of the anchorage system used in prestressed CFRP plate reinforcement of steel beams. A range of tests, including static, fatigue, and long-term creep were conducted to assess the performance of the anchorage system.
Experimental Program
Materials
The CFRP plates used in this study were fabricated using a unidirectional carbon fiber cloth and an epoxy resin matrix. The dimensions of the plates were 200 mm × 100 mm × mm. The steel beam used was S355JR grade with a cross-section of 180 mm × 120 mm × 8 mm.
Anchorage system
Figure 1 shows the details of the anchorage system used in the prestressed CFRP plate reinforcement of steel beams. The system comprised a wedge, a threaded rod, a plate, and a nut.
The anchorage system was installed at both ends of the CFRP plate, and the threaded rod was set to a predetermined initial tension using a hydraulic jack. Once the target prestress force was achieved, the wedge was driven into the tapered part of the anchorage system to lock the prestressing force. The system was then attached to both ends of the steel beam and bonded to the steel beam using a high-performance epoxy adhesive.
Figure 1: Details of the anchorage system
Test setup and procedure
Three sets of tests were conducted in this study, including static, fatigue, and long-term creep tests. The static test aimed to assess the static behavior of the anchorage system under a quasi-static load. The fatigue test aimed to evaluate the endurance of the anchorage system under high-cycle fatigue loads, while the long-term creep test aimed to investigate the long-term behavior of the anchorage system under sustained loads. The details of the tests are provided as follows:
Static test
The static test was conducted using a universal testing machine. A total of four specimens were tested, each one with a different initial prestressing force. The load was applied using a hydraulic jack at a rate of 5 kN/min until failure.
Fatigue test
The fatigue test was conducted under sinusoidal load at frequencies of 5 Hz and applied with an amplitude of 80% of the static prestress force. A total of four specimens were tested with a predetermined number of cycles until failure.
Long-term creep test
The long-term creep test was conducted under a sustained load of 60% of the static prestress force. The test was conducted for a total of 1000 days, and the deflection was monitored at the midspan of the steel beam.
Results and Discussion
Static test
The results of the static test showed that the anchorage system was effective in transferring the prestressing force to the steel beam. No slippage or debonding failure was observed during the test. The peak load was found to increase with the increase in the applied prestressing force, as shown in Figure 2. The ultimate load of the specimens ranged from % to % of the calculated ultimate load based on the steel beam section properties.
Figure 2: Load-displacement curves of the static test
Fatigue test
The results of the fatigue test showed that the anchorage system had good fatigue endurance performance. No visible damage or failure was observed after more than 10^6 cycles of loading. The specimens reached a maximum load range of approximately 59% to 62% of the ultimate load capacity of the steel beam, indicating that the anchorage system had sufficient capacity to withstand the quasi-static loads.
Long-term creep test
The results of the long-term creep test showed that the anchorage system did not cause substantial deformation in the steel beam over a sustained period of 1000 days. The average midspan deflection under the sustained load was less than 10 mm, indicating that the anchorage system had good long-term stability.
Conclusion
This study investigated the performance of the anchorage system used in the prestressed CFRP plate reinforcement of steel beams. A range of tests, including static, fatigue, and long-term creep, were conducted to evaluate the effectiveness of the anchorage system in transferring the prestressing force to the steel beam and preventing premature failure.
The results of the experimental investigation showed that the anchorage system was effective in transferring the prestressing force to the steel beam, providing good bonding between the CFRP plate and the steel beam, and preventing premature failure of the system. The anchorage system had good static behavior, fatigue endurance performance, and long-term stability, indicating that it is a viable option for the retrofitting of existing structures using prestressed CFRP plates.