Experimental and analytical studies on reinforcement effects of FRP-strengthened externally structures with FRP pre-tension

1)先张法FRP布加固效果的试验研究：定量验证了先张法FRP布加固对FRP加固混凝土和钢筋混凝土梁的承载能力(极限强度)、刚度特性和抗裂性能的影响，以及对钢筋屈服荷载、减振效果和延性性能的改善。主要参数包括混凝土抗压强度、FRP片材的数量和种类、粘结面的处理方法和预应力水平。此外，还研究了不同预压损伤试件的加固效果。通过这一试验方案，证实了通过FRP预应力可以大大提高现有FRP粘结技术的效率。另一方面，作为一种合适的增强材料，HIG-…对PBO纤维片材的增强效果也较好2)先张法FRP片材的锚固处理：为避免预应力释放后在端部发生剥离破坏，采用U型或扁平FRP片材粘结、锚杆锚固等加固方法对锚固区进行加固处理，并对各种加固方法的效果进行了讨论。此外，还提出了在锚固区周围设置一层滞后的剪应力集中的减应力策略。3)外贴FRP片材的粘结和剥离机理：首先，根据已有的和新开展的实验结果，识别了不同类型的剥离破坏模式。然后，针对界面断裂的脆性特征，发展了基于断裂力学的理论和数值分析方法，对有无预拉的FRP加固结构进行了分析和评估。4)FRP片材和FRP加固结构的蠕变和应力松弛行为：通过试验研究，掌握了碳纤维和PBO纤维增强聚合物片材在1000小时内的蠕变和应力松弛行为。5)FRP预拉加固结构的性能验证：通过对FRP加固结构的钢筋屈服-FRP断裂、钢筋屈服-混凝土破坏、混凝土不同时破坏、剪切破坏和剥离破坏等不同破坏模式的研究，验证了传统RC理论的适用性。在此基础上，提出了一种基于断裂力学的合理设计方法来预测脱粘裂缝的变形和极限荷载。此外，还对FRP片材的合理预应力水平的确定和配筋的结构优化进行了探讨。较少

1) Experimental investigation on reinforcement effects of pre-tensioned FRP sheets : An experimental program was carried out to verify quantitatively the reinforcement effects on load-carrying capacity (ultimate strength), stiffness characteristics and resistance of crack opening, and the improvements on yield load of rebars, vibration mitigation effect and ductility behavior, of FRP-strengthened concrete and reinforced concrete beams through FRP pre-tension. The main parameters were the concrete compressive strength, the number and the types of FRP sheets, treatment methods of bonding surface and the pre-stress level. Moreover, the reinforcement effects of specimens with different existing damages due to pre-loading were also investigated. Through this test program, it was confirmed that the efficiency of the existing FRP bond technique could be improved greatly through FRP prestressing. On the other hand, as an appropriate reinforcement, the effectiveness of PBO fiber sheets with hig … More her energy absorption is also verified for future practical use.2) Anchorage treatment of pre-tensioned FRP sheets externally bonded : To avoid the debonding failure near the ends upon releasing the pre-tensioned force, the anchorage zone are dealt with by several proposed reinforcing methods such as bonding with U type or flat extra FRP sheets, anchorage with anchor bolts, and the effects of these anchorage treatments were also discussed. Besides, a stress reduction strategy for the shear stress concentration with a layer lag around anchorage zone is proposed. Except the theoretical analysis, experimental investigation was also used to verify the effectiveness elementarily.3) Bonding and debonding mechanism of externally bonded FRP sheets : First of all, the different types of debonding failure modes were identified through the existing and newly carrying out experimental results. Then, due to the brittle behavior of interfacial fracture, the fracture mechanics based theoretical and numerical methods were developed for analyzing and evaluating the FRP-strengthened structures with or without FRP pre-tension. Moreover, an experimental program was also performed to identify the constitutive model of local shear stress-shear displacement relationship.4) Creep and stress relaxation behavior of FRP sheets and FRP-strengthened structures : Through experimental investigation, the creep and stress relaxation behavior of carbon and PBO fiber reinforced polymer sheets up to 1000 hrs has been grasped. Moreover, the creep and stress relaxation behavior of FRP-strengthened concrete beams was also investigated within a short-term up to a couple of month.5) Performance verification of FRP-strengthened structures with FRP pre-tension : Through the investigation of different failure modes of FRP-strengthened structures, such as rebar yielding-FRP rupture, rebar yielding-concrete crushing, concrete crushing without both FRP rupture and rebar yielding, shear failure and debonding failure, first of all, the applicability of traditional RC theories were verified. Then, a rational design approach based on fracture mechanics for predicting the deformational and ultimate load due to debonding fracture was proposed. Besides, an effort was also made to investigate the determination of appropriate prestressing stress level of FRP sheets and structural optimization of reinforcement. Less