斜向U型箍限制混凝土保护层剥离的试验研究

Suppression of Concrete Cover Separation in FRP-Plated RC Beams Using FRP U-Jackets

混凝土保护层剥离破坏是树脂基纤维增强复合材料(以下简称"复材")受弯加固钢筋混凝土梁的常见破坏模态。它以复材底板端部附近出现弯剪裂缝作为起裂标志,伴随着关键水平裂缝于复材底板端部的受拉纵筋高度的出现和发展,以及由此导致的混凝土保护层剥离。混凝土保护层剥离发生时,复材底板的最大拉应变通常仅为其极限抗拉应变的20%～40%,导致复材的抗拉强度得不到充分利用。为此,各国学者提出了不同形式的锚固措施,如金属锚具、竖向U型箍等,并进行了广泛的研究。其中,斜向U形箍施工最为便捷、耐久性能最为优越,具有大力推广应用的潜能。通过一系列试验,证明了斜向复材U型箍能够成功限制混凝土保护层剥离破坏,从而显著提升加固梁的极限承载能力和延性。

Concrete cover separation commonly controls the failure of a reinforced concrete(RC)beam strengthened with a fibre-reinforced polymer(FRP)plate. Such a failure mode of FRP plated RC beams often occurs with the maximum strain of the FRP soffit plate being about 20%~40% of its tensile rupture strain,and make it become an impediment to fully utilize the high tensile strength of the expensive FRP material. The postponement or suppression of concrete cover separation failure using appropriate anchorage measures has therefore attracted increasing research attention. While a number of options (e.g.,fibre anchors) is possible to delay/suppress this failure mode,inclined FRP U-jacketing at the end of the FRP soffit plate is among the most effective and easily-installed ones. Through a series of tests,it is proved that the oblique composite U-shaped hoop can successfully limit the peeling damage of the concrete protective layer,thereby significantly improving the ultimate bearing capacity and ductility of the reinforced beam.