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The research on seismic retrofit of RC members using continuous fiber sheets is rapidly advancing in Japan. These research activities have been accelerated since the Hanshin-Awaji Earthquake, 1995 because this retrofitting technique has an advantage due to lightweight, flexibility, non-welding, and easy handling in construction works. The most preferable retrofitting technique for the existing building being in use is jacketing RC columns with carbon or aramid fiber sheets because of the advantage above. Recently many results of the research on short column with spandrel wall, columns with wing wall, beams with slab (T shaped beam), earthquake resisting wall have been reported in Japan. This paper introduces, first of all, these experimental research results in detail and the seismic retrofitting effects by the continuous fiber sheets are comprehensively evaluated. Flexural capacity, shear capacity and the improvement of ductility are discussed to evaluate the effect of reinforcement of continuous fiber sheets. Then, methods for evaluating the seismic retrofit of regular columns with continuous fiber sheets are described. A basic idea of the evaluation method proposed for a regular column is shown, and the problems which should be examined are extracted and explained about these effects. As the summary, the problems which should be solved, research direction and prospect are pointed out for the future research on seismic retrofit by continuous fiber sheets. Research needs for establishment of a design method when various members are reinforced by continuous fiber sheets in the future are also discussed.

Fiber Reinforced Polymer (FRP) composites are a very promising alternative to the use of traditional materials and methods in the repair and strengthening of under-designed or deteriorating structures. While most results indicate that strengthening with FRP is very effective, the wide variety of testing techniques used among researchers makes it very difficult to compare results. Objectives of this research were to gain a broader understanding of FRP’s effects on the failure modes and performance of reinforced concrete beams, to investigate a variety of strengthening schemes, and to validate current design methods used for shear and flexural strengthening of reinforced concrete members. This was achieved by comparing a variety of FRP systems under similar conditions. The seventy-one specimens tested exhibited a variety of failure modes depending on the strengthening scheme, thickness of the laminates, and material (carbon or glass fibers). The beam failure modes showed strong dependency on the FRP thickness. As the thickness of the composite laminate increased, debonding or concrete shear failure dominated. The effectiveness of FRP reinforcement was studied as a function of FRP rigidity and the effective strains developed in the fibers.

The technical research committee on continuous fiber (CF) sheet in the Japan Society of Civil Engineers (JSCE) has been engaged in making a new design system for concrete structures retrofitted with externally-bonded CF sheets since 1998. This paper presents the framework and some tentative contents of the design system. The system is on the basis of the concept of performance-based design, in which a structure to be retrofitted is systematically verified if it can satisfy any required performance items during the residual service life. Performance items of structures are verified in terms of the verification index which represents each performance item quantitatively. Evaluation methods for several performance items under development are shown in this paper regarding structural safety and serviceability of structures. The importance of precise prediction of peeling-off of CF sheet from concrete is emphasized. In the verification process of performance items, time-dependent performance changes due to environmental and loading attack are taken into account, so that structural and durability design are unified in a rational way.

AFRP tensile elements (bars, strands etc.) can be successfully applied for the pre-tensioning of precast concrete members, for post-tensioning tendons, ground anchors etc. In such applications, the AFRP may come into permanent contact with the alkaline pore solution of concrete or cementitious grout. Many tests prove that such aggressive environment may seriously damage the stressed AFRP and significantly abbreviate its lifetime due to premature stress rupture. The stress rupture strength of FRP is the relevant durability property to ensure the serviceability and safety of a structural concrete member during its service life. The stress rupture behaviour is usually studied on stressed AFRP bars placed in aggressive solutions etc.. It is though evident that such severe environment does not realistically reflect the true environment of AFRP in dense concrete and grout. It is was therefore the aim of the authors to develop - on basis of experiments in several stages and by theoretical studies - an engineering model for the prediction of the stress rupture strength of stressed AFRP in concrete or grout. This model was verified by tests. Provided the stress rupture strength of AFRP in dry air or in alkaline solution etc. was experimentally established afore-hand, the parameters of the mean stress rupture relationship can be sharpened. Additional deliberations are however necessary to transfer the model into the real environment of concrete or grout around the FRP element. Suitable procedures are presented.

Using the database consisting of 236 R/C column specimens conducted in Japan, the characteristic behaviors of strengthening by fiber wrapping were analyzed. The following findings were obtained: (1) The amount of shear reinforcement, the span to depth ratio, the axial compressive stress level influence on the strength and deformation capacities of retrofitted columns by fiber sheet wrapping (2) Shear strength of retrofitted columns can be predicted by previous design equations based on the strut and tie models as same as for usual R/C columns, in which the effective fiber strains of about 1% is appropriate. (3) There are few test data about the confining effect of fiber sheet wrapping on bond resistance of longitudinal bars. Further research effort is required to evaluate the shear strength of columns governed by the splitting of cover concrete along longitudinal bars. (4) The ductility ratio can be roughly estimated as a function of the shear to flexural strength ratio. (5) For the specimens with plain round longitudinal bars, the previous equations based on the strut and tie model cannot be applied because of the poor bond capacity.