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

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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