Deflection calculating method of damaged concrete beams strengthened with BFRP

In order to accurately calculate the deflection of damaged concrete beam strengthened with basalt fiber reinforced plastics (BFRP) and provide theoretical foundation for the design and construction of the beam, according to different reinforcement ratios, eleven test beams with different amounts of strengthened BFRP sheet and loading methods were designed. The load-deflection curves of different test beams were obtained. Under different pre-loading programs, the changing rules of deflection of un-strengthened beams, strengthened beams with one layer and two layers of BFRP sheet were analyzed respectively. The calculation formulas of mid-span deflection of damaged concrete beam strengthened with BFRP were presented, and the calculated deflections and measured values were compared. Analysis result indicates that the deflections of damaged concrete beams strengthened with BFRP are influenced by initial load and amount of BFRP sheet layer. The deflections of strengthened beams with initial load increase by 30%-94% compared with strengthened beams without initial load, and the deflections of strengthened beams with two layers of BFRP sheet increase by 19%-42% compared with strengthened beams with one layer of BFRP sheet. The impact of post-strain of BFRP should be considered in deflection calculation. The average value of the maximum difference between the calculated deflection and measured value is 7.26 mm. When the initial load is small and the reinforcement ratio is high, the calculated deflection of concrete beam is closer to the measured value, and the method can be used in the engineering practice.