剪跨比主导下FRP加固钢筋混凝土梁抗剪机理及剥离控制研究

The shear mechanism and the debonding-restriction of RC beams strengthened with externally bonded (EB) FRP in consideration of the single effect of the dominate factor of shear span ratio and the coupling effects of shear span ratio and the other critical factors such as size effect, shear steel reinforcement ratio and a FRP strip anchor, will be investigated in this project. Based on a series of experimental and analytical studies, following anticipated achievements are made: (1) the effect of the shear span ratio on the shear performance of FRP strengthened RC beams is clarified and thus a theoretical model for shear contribution of FRP reinforcement under different shear span ratio is developed; (2) the size effect of RC beams and the influence of the shear steel reinforcement ratio on the shear performance under different shear span ratio is explored respectively; (3) a new hybrid bonded system using FRP strips as anchors for restricting the debonding of FRP is developed; the bond-slip relation model of FRP-to-concrete interface of concrete structures strengthened with hybrid bonded FRP is derived and hence the mechanism of the FRP strip anchor in controlling the debonding of FRP and the distribution of the FRP strip anchors in the hybrid bonded system is clearly understanding; (4) and finally, based on the above achievements, the FRP efficient strain model is derived upon which a shear design method of FRP strengthened RC beams in considering all the critical factors is developed. The aforementioned achievements of this project can have a great contribution in the promotion and development of design and construction of concrete structures shear-strengthened with EB-FRP and thus provides a stable academic foundation for the application of FRP material in the rehabilitation of civil engineering structures.

本项目重点以剪跨比为主导，协同考虑尺寸效应、配箍率、FRP锚固压条等因素与其耦合作用开展FRP加固钢筋混凝土梁的抗剪机理及限制FRP剥离破坏的控制机制等方面的研究。项目拟以试验研究为基础，结合理论和数值分析方法，阐明剪跨比对FRP加固钢筋混凝土梁抗剪性能的影响机理和规律，建立引入剪跨比的FRP抗剪贡献的计算模型；揭示由剪跨比引起的不同剪切破坏模式下分别考虑尺寸效应及配箍率因素的FRP加固钢筋混凝土梁的抗剪机理和规律；建立FRP压条锚固区内FRP-混凝土界面粘结-滑移关系模型，明晰FRP锚固压条限制剥离破坏的控制机制及配置模式。在上述研究基础上，建立综合考虑多因素影响下的FRP有效应变计算模型，最终提出多因素影响下的FRP抗剪加固设计方法。本项目预期的研究成果是对现有FRP抗剪加固理论的拓展和提升，对FRP加固混凝土结构的设计、施工和工程实际应用提供了系统、科学的参考依据。

针对目前FRP外贴抗剪加固混凝土构件研究现状存在的不足之处，本项目重点以剪跨比为主导，协同考虑尺寸效应、配箍率、FRP锚固压条等因素与其耦合作用开展FRP加固钢筋混凝土梁的抗剪机理及限制FRP剥离破坏的控制机制等方面的研究。. 通过21根不同剪跨比的FRP加固梁，阐明了剪跨比对FRP加固钢筋混凝土梁抗剪性能的影响机理和规律，并建立了引入剪跨比的FRP抗剪贡献的计算模型；对16根不同剪跨比、截面尺寸以及加固方式的试验梁进行试验研究，揭示了由剪跨比引起的不同剪切破坏模式下分别考虑尺寸效应的FRP加固钢筋混凝土梁的抗剪机理和规律，U形FRP条带抗剪作用的效率与试验梁的尺寸有关，而尺寸对全包裹FRP条带的加固效果影响并不明显；基于25根不同配箍率加固梁的试验研究，发现FRP抗剪贡献随着剪跨比的增大呈递增的趋势，随配箍率的增大而呈递减的趋势，且外贴FRP条带会限制箍筋应变增长；利用96个不同锚固压条形式的单剪试验以及60个不同混凝土强度和FRP粘结长度的单剪试验，研究发现施加FRP锚固压条可以有效提高单剪试件FRP条带的极限荷载、有效应变及有效粘结长度。同时，证实了锚固压条作用下单剪试件极限荷载的提高量与锚固重叠区的骨料咬合作用密切相关，明晰了FRP锚固压条限制剥离破坏的控制机制及配置模式。在上述各项研究基础上，结合收集到的数据库发现，FRP抗剪贡献受到混凝土强度、剪跨比、梁尺寸、配箍率、配布率、加固方式等很多因素影响，现有规范对这些因素考虑并不全面，通过理论分析结合现有规范验证已有数据库，建立了综合考虑多因素影响下的FRP有效应变计算模型，最终提出多因素影响下的FRP抗剪加固设计方法。. 本项目的研究成果不仅可以拓展和提升FRP抗剪加固理论，对推动FRP在结构加固领域乃至整个土木工程界的广泛应用奠定坚实的理论基础。相关成果亦可以直接应用于指导FRP加固的设计和施工，提升了FRP抗剪加固技术的工程实际应用价值，具有重要的社会影响和经济价值。