纤维带绕结自锁机理及其混锚加固混凝土受弯构件性能提升研究

High-performance laminates of fiber reinforced polymer have been increasingly exploited to strengthen reinforced concrete structures. When they are just bonded on the substrate, however, brittle failures called premature debonding very often occur on the FRP-concrete joints, unbeneficial to efficient employment of the materials adopted and reliable service of the structures strengthened. The proposer happened to fortunately invent an anchorage technique to self-lock the ends of strip of fiber sheet, whose use in combination with usual bonding results in a hybrid anchored FRP system. The preliminary experiments showed that it can effectively prohibit the end debonding. The self-locking device has been recently optimized to be a slotted plate that is compact and only several mini-meters thick, which would extremely facilitate the field operation for engineering and enable slight pretension of FRP strips. As compared to conventional bonding, hybrid anchorage enable significant promotion of behavior for the strengthened members by improving the stress condition at some important locations. Fundamental research will be conducted in this project for application of the novel technique. It involves several types of tests particularly designed, theoretical analyses and numerical simulation. The mechanism of self-locking the strip by specially wrapping will be explained in detail. Specific way will be recommended to examine the mechanical property of the end-anchored FRP system. The characteristics and design of the anchorage in concrete near the plate will be studied. Effect of the ratio of span to section depth on the FRP stress at intermediate debonding will be investigated for flexural member so strengthened. Approaches will be found to evaluate not only the ultimate capacity but also the ductility. The objectives are to get in-depth understanding of the mechanism of debonding restraint and present design method for strengthening with the new technique so as to ensure both economy and reliability when it is used.

高性能纤维增强复合片材在混凝土结构加固工程中应用渐多，但纯粹粘贴时，纤维片材-混凝土界面特别容易过早发生脆性的剥离破坏，不利于材料的充分利用和结构的可靠使用。申请者幸运地发明了带状纤维布端部自锁锚固技术，附带端锚粘贴即形成混锚系统，初步试验表明混锚能够有效抑制端部剥离。近期将自锁装置优化为毫米级紧凑型开缝锚板，极大方便了工程应用，还能对纤维带进行微张拉。混锚微张拉相比传统粘贴，可通过改善关键部位的受力条件实现加固构件性能的更大提升。本项目对该加固技术开展应用基础研究，通过专门设计的多种试验，加上理论分析和数值模拟，研究纤维带绕结自锁机理、端锚纤维带力学性能检验方法、端锚系统受力特点及其拉剪共同作用下的锚固性能与设计要求、受弯构件跨高比对中部剥离应力的影响、剥离后破坏延性及极限承载力算法，以取得对其抗剥离机理的深入认识，并提出相应的加固设计方法，从而确保应用该技术既经济合理又安全可靠。

碳纤维布等高性能纤维增强复合片材在结构加固工程中应用日益广泛，但仅依靠粘贴时，片材-构件界面特别容易过早发生脆性的剥离破坏，不利于材料的充分利用和结构的可靠服役。项目负责人发明了柔带端部绕结自锁法，并将自锁锚固装置优化为毫米级紧凑型开缝板，纤维布带此端锚粘贴即形成混合锚固系统。项目负责人推导了柔带以特定方法缠绕开缝板时纵向应力随锚板曲面弯转而变化的理论公式，设计并制作了纤维带与锚板之间、相邻层纤维带之间的摩擦系数测试装置，获得了摩擦系数测试结果，揭示了纤维带绕结自锁机理，明确了纤维带绕开缝板自锁的条件，发明了通过纤维带-端锚组装件试验对端锚纤维带的材料利用效率进行检验的方法和装置，发现碳纤维带端绕开缝板自锁后的强度利用率可达95%以上；验证了纤维带端部绕结自锁锚固系统的受力特点及内力关系，提出了拉剪共同作用下该锚固系统用于混凝土梁时的设计方法；将碳纤维带混锚加固技术用于混凝土结构中量大面广的梁和板，开展了系统深入的应用基础研究，阐明了端绕开缝板锚固对界面剥离的防治机理，弄清了受弯构件和纤维带的纵向尺度对中部剥离性能的影响方式；发现跨高比主要通过剪跨比对纤维带中部剥离应变产生影响，二者呈减函数关系，考虑剪跨比影响提出了剥离应变计算公式；证实了在合理范围内缩短纤维带长度不仅可以节约材料用量，还能如所预期提高承载能力，这与纯粘加固时的变化规律正好相反，却能产生经济效益；建立了中部剥离后破坏延性及极限承载力算法，为混凝土受弯构件性能提升设计提出了新型高效的成套方法，为指导工程实践提供了技术指南，为编修相关规范提供了科学依据。研究成果已在实际工程中得到应用，不仅拓宽了先进复材的应用范围，而且突破了现行规范对其应用条件的限制，若经大力推广，将带来显著的经济价值和社会效益。