Abstract This paper presents the results of an experimental study designed to investigate the performance of reinforced concrete (RC) beams strengthened with fibre-reinforced polymer (FRP) sheets subjected to wetting–drying cycles and a sustained load. Twenty-one RC beams were manufactured and externally bonded with carbon-FRP (CFRP) or glass-FRP (GFRP) sheets. Two U-shaped FRP anchorages were also applied on the ends of the beams to prevent end peeling failure. The FRP-strengthened beams were subjected to combined wetting–drying cycles in 5% NaCl solution and sustained loads for 0, 90, 180, and 360 days at load levels of 0%, 30%, and 60% of the ultimate loading capacity of the unstrengthened beam. During this period, the mid-span deflections and cracks of the beams were monitored, following which the beams were monotonically loaded to failure under a four-point bending. The failure patterns, mid-span deflections, and debonding loads were also examined. The test results showed that during sustained loading, the time-dependent and residual deflections of the FRP-strengthened RC beams increased with the increase in their periods of sustained loading and load levels. Intermediate crack-induced (IC) debonding of the CFRP-strengthened RC beams was induced by concrete separation and CFRP–concrete interface debonding, whereas that of the GFRP-strengthened RC beams was mainly caused by GFRP–concrete interface debonding. Combined wetting–drying cycles and a sustained load had an adverse effect on the yielding and debonding load of the FRP-strengthened RC beams, and the ductility of the GFRP-strengthened RC beams was higher than that of the CFRP-strengthened beams. In addition, a model considering the effects of wetting–drying cycles and sustained loads was proposed to predict the debonding load of FRP-strengthened RC beams, and it showed a reliable prediction.

中文翻译：

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干湿循环和持续载荷对 FRP 加固 RC 梁性能的综合影响

摘要 本文介绍了一项试验研究的结果，该研究旨在研究用纤维增强聚合物 (FRP) 板加固的钢筋混凝土 (RC) 梁在干湿循环和持续载荷下的性能。制造了 21 根 RC 梁，并在外部使用碳 FRP (CFRP) 或玻璃 FRP (GFRP) 板粘合。梁的端部还应用了两个 U 形 FRP 锚固件，以防止端部剥落失效。FRP 加固梁在 5% NaCl 溶液中进行联合干湿循环，并在 0、90、180 和 360 天的载荷水平下承受 0、90、180 和 360 天的极限载荷能力。未加强的梁。在此期间，监测了梁的跨中挠度和裂缝，随后，梁在四点弯曲下单调加载至破坏。还检查了破坏模式、跨中挠度和脱粘载荷。试验结果表明，在持续加载过程中，玻璃钢加固钢筋混凝土梁的时变挠度和残余挠度随着持续加载时间和荷载水平的增加而增加。CFRP 加固 RC 梁的中间裂纹引起（IC）脱粘是由混凝土分离和 CFRP-混凝土界面脱粘引起的，而 GFRP 加固 RC 梁的中间裂纹引起（IC）脱粘主要是由 GFRP-混凝土界面脱粘引起的。联合干湿循环和持续载荷对 FRP 加固 RC 梁的屈服和脱粘载荷产生不利影响，GFRP 加固 RC 梁的延性高于 CFRP 加固梁。此外，还提出了一个考虑干湿循环和持续荷载影响的模型来预测 FRP 加固 RC 梁的脱粘荷载，并显示出可靠的预测。