混锚预应力U形碳纤维条带抗剪加固混凝土梁试验研究

研发钢筋混凝土梁抗剪加固用U形纤维增强复材（FRP）条带的预应力系统，提出一种预应力U形条带端锚与黏贴并用（简称混锚）的抗剪加固方法。完成了1根未加固、7根采用U形碳纤维（CFRP）条带进行抗剪加固的矩形截面梁剪切试验，加固梁中1根为纯黏贴、6根为混锚预应力。结果表明：混锚预应力加固在抑制主斜裂缝开展、延缓箍筋屈服和提高箍筋塑性利用率等方面的表现均优于纯黏贴加固，能够防止FRP端部剥离并实现拉断破坏，大幅度提高纤维强度利用率，显著提高梁的抗剪承载力，最大提升率达92%。预应力和配纤率的大小对抗剪加固效果有较明显影响，其他条件相同时，预应力越大或配纤率越高，加固梁综合性能越好。建议了混锚预应力U形CFRP有效应变的计算公式，用于预测剪切破坏时CFRP的贡献和加固梁的承载能力，与试验结果符合良好，可供工程应用参考。

Experimental study on shear performance of RC beams strengthened with hybrid-anchored and prestressed CFRP U-strips

U-strips of fiber reinforced polymer (FRP) are usually used for shear strengthening of reinforced concrete beams. A novel prestressing system with hybrid anchorage is proposed, in which the prestressed FRP is bonded to beam surfaces and the ends are anchored by interlocking. Eight rectangular beams were tested to validate the feasibility of the new method, including one control beam, one strengthened with bonded CFRP U-strips and six strengthened with hybrid-anchored and prestressed CFRP U-strips. The results show that the proposed prestressing method performs much better than externally bonding in the aspects of restraining the propagation of diagonal cracks and improving the strain behavior of steel stirrups. The end-debonding of CFRP can be shifted to rupture failure, the fiber-strength utilization can be significantly enhanced, and the shear capacity of RC beam can be increased with the maximum increase rate about 92%. The strengthening effect is related to the area ratio and the prestress of CFRP. Raising area ratio or prestress value is helpful to improve the comprehensive performance of the strengthened beams. Furthermore, a formula for calculating the effective strain of prestressed CFRP was proposed and then used to calculate shear capacities of the strengthened beams. The calculated capacities are all in good agreement with the test results, indicating that the formula can serve as a rational reference for engineering application.