| In order to improve the efficiency of concrete structures strengthened with sole fiber reinforced plastic(FRP),a new idea strengthening concrete structures with hybrid fiber reinforced plastic(HFRP) was proposed in this thesis firstly.As the first part of a large research program, a comprehensive analysis into the working mechanism and properties of HFRP materials was performed, and it was decided to cooperate imported carbon fiber(CF) and homemade ordinary glass fiber(GF) for making HFRP to be suitable for strengthening concrete structures. Test results of various HFRPs with lower cost than CFRP showed that the developed strength and the elongation of CF in HFRP is much higher than those in sole CFRP. Furthermore, A new concept and research imagining - prestressed HFRP was put forward as well.Basing on the results of material test research, the ductility, load carrying capacity, strengthening cost and the developed efficiency of FRP were chosen to be the indices, for a comparison experimental study including CFRP, GFRP and C/G HFRP strengthened concrete beams. Test results showed that the C/G HFRP could fully develop the advantages of both CF and GF and overcome shortages exist in sole FRP.Under the premise increasing load carrying capacity with same degree, HFRP could lead a both significant increase of rupture strain and deformation capacity and a notable decrease of strengthening costs ;and the stiffness of the HFRP strengthening beams just a little lower than that of CFRP strengthening beams. A design method for HFRP strengthening beams was presented.Noticing that debonding between CFRP and concrete was the main failure mode of flexural, and HFRP strengthening beams had larger deformation capacity than CFRP strengthening beams, a research study for improving bond quality was carried out. After analyzing bond mechanism and existed bonding methods, it was pointed out that no bond pressure(one of the there key factors controlling bond strength)was responsible for lower bond strength, A simple and feasible method for exerting bond pressure by using air cushion was proposed. Test Results of small specimens showed that debond failure and delaminate failure could be avoided provided bond pressure was near to 0.3 kg/cm2.As a result, this bonding method was applied to middle size beams and led to a good results.Further, HFRP strengthening technology was used to strengthen concrete square columns. The result of comparison test showed that, with a same degree of increased load carrying capacity, HFRP strengthening square column have larger deformation capacity and lower cost than CFRP strengthening square column.Intended to improve the strengthening efficiency of the column more significant, an idea to strengthen concrete square column by using prefabricated HFRP circular tubes was proposed. Test results show that, changing the column shape from square into circular led a more significant increase of the load carrying capacity. HFRP strengthening columns not only performed a lager deformation capacity and a lower cost than CFRP strengthening square columns, but also exhibited a "yield" stage, expressing much higher reliability. The distinctive working mechanism of HFRP strengthening columns was analyzed, and an ultimate strength mode and a tri-liner stress-strain model were put forward correspondingly.During a practice of shear strengthening reinforced concrete beams, the designmethod suggested by ACI 440 committee and Chinese standard was found not reliable. Reliable method was, therefore, proposed and applied in the practical design and construction. In view that CFRP bundles of shear strengthening beams were fracture one by one, it was pointed out that the effective way to increase strengthening efficiency is to use HFRP with "yield" feature.At last some research imagination for future were presented: firstly according to the developing plan of the national building material industry, high strength glass fiber will be developed with great effort, the high strength glass fiber is...
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