持载混凝土梁端锚无黏结预应力U形碳纤维带受剪加固试验研究

利用已研发的适用于U形纤维增强复材(FRP)的端锚无黏结预应力系统，对1根未加固梁及6根预应力碳纤维(CFRP)条带加固的不同持载水平钢筋混凝土梁进行受剪性能试验，探究端锚无黏结预应力加固法的有效性。研究结果表明：该方法能够对不同持载水平混凝土梁进行有效加固，可避免条带的端部剥离破坏并实现拉断破坏，提高纤维强度利用率，延缓箍筋屈服，抑制梁刚度的退化和斜裂缝的开展，提升构件受剪承载力，最大提升率约75%；预应力加固效果易受持载水平和配纤率影响，其他加固参数相同时，较高持载水平和配纤率的加固梁受剪性能更好，受剪承载力提高幅度更大。端锚无黏结预应力U形CFRP条带加固梁受剪承载力计算结果与实测结果吻合较好，可为加固设计提供参考。

Experimental research on shear strengthening of concrete beams under sustained load with end-anchored and unbonded prestressed CFRP U-strips

Using an end-anchored and unbonded prestressing system for fiber reinforced polymer (FRP) U-strips, seven beams were tested to validate the feasibility of the strengthening method, including one control beam and six strengthened beams under different sustained loads with prestressed CFRP U-strips. The results show that this method can effectively strengthen concrete beams under different levels of sustained loads. It can shift the end-debonding failure of CFRP to the rupture failure and thus greatly improve the utilization of strength of CFRP. It can also delay the yield load of steel stirrups, restrain the degradation of stiffness and the development of shear cracks, and significantly increase the shear capacity of concrete beams by up to 75%. The strengthening effect is found to be related to the level of sustained loads and the area ratio of CFRP. With the same strengthening parameters, the increase of sustained load level or area ratio leads to an increase of the shear capacity of beams. The calculated results are in good agreement with the test result about the shear capacity of the strengthened beams with end-anchored and unbonded prestressed CFRP U-strips, which can provide a reference for the design of the strengthening system.