Numerous theoretical and experimental studies have been conducted on fiber-reinforced polymer (FRP) shear strengthening rectangular and T-section beams; however, few researches focused on box beam, which is widely used in bridge superstructures. This paper presented experimental study on shear strengthening reinforced concrete (RC) box beam by carbon-fiber-reinforced polymer (CFRP) with four common strengthening patterns. The CFRP strengthening schemes, failure modes, deflection, and effective strain in fibers were investigated and recorded. As for CFRP shear contribution, it showed best performance with a 52.7% increase for the specimen with a continuous U-jacket sheet. Besides, all the strengthened RC box beams exhibited the debonding of CFRP strips or sheets in the ultimate state. It was found that the maximum strains in fiber recorded from strengthened specimen were approximately 3000με accounting for 17% of the ultimate strain of CFRP sheet. The model in fib Bulletin 90 was used to predict CFRP shear contribution in the strengthened specimen, but it overestimated the values compared with experimental results because of higher effective strain calculated by model. A coefficient of 1.31 was therefore proposed for the equation of effective strain in the model, and the calculated CFRP shear strength by fib Bulletin 90 combined with modified effective strain was in good agreement with the experimental values.

已经对纤维增强聚合物（FRP）抗剪矩形和T型截面梁进行了许多理论和实验研究。然而，很少有研究集中在箱梁上，箱梁被广泛地用于桥梁上部结构中。本文介绍了碳纤维增强聚合物（CFRP）用四种常见的加固方式对钢筋混凝土（RC）箱形梁进行剪力加固的试验研究。研究并记录了CFRP的加固方案，破坏模式，挠度和有效应变。至于CFRP剪切贡献，它表现出最好的性能，连续U型夹层板的试样增加了52.7％。此外，所有加固的RC箱形梁在极限状态下均表现出CFRP条或板的剥离。με占CFRP薄板极限应变的17％。fib Bulletin 90中的模型用于预测加固样品中的CFRP剪切贡献，但由于模型计算出的有效应变更高，因此与实验结果相比，该值被高估了。因此，该模型中的有效应变方程的系数为1.31，由fib Bulletin 90结合修正的有效应变计算得出的CFRP剪切强度与实验值非常吻合。