2005, Volume 7, Issue 9
Strategic Study of CAE >> 2005, Volume 7, Issue 9
Study on Strengthening Technique with Prestressed PBO Fiber Sheets
Department of Urban & Civil Engineering, Ibaraki University , Hitachi 316-8511, Japan
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Abstract
The application of externally bonded fiber reinforced polymer (FRP) laminates to the exposed faces of concrete members provides an innovative and efficient rehabilitation method for strengthening and upgrading structurally inadequate or functionally obsolete concrete structures. However, FRP laminates unlike the cold worked steel exhibit elastic-rupture behavior and also the limited bond capacity of FRP-concrete interface often fails the retrofitted system in an undesirable brittle manner, which leaves FRP material unused with more reserves. Moreover, enhancements in cracking and yield load due to FRP bonding are not significant. To take full advantage of FRP laminates, more gains can be achieved by prestressing the fibers prior to bonding them. Traditional practice is to pretension fiber sheets impregnated with adhesive or FRP plate, which is time-consuming, difficult to apply in the field and ensure a perfect bond at the interface. A newly-developed PBO fiber possesses high modulus, high strength and higher energy absorption capability as compared to carbon and aramid fibers, and PBO fiber sheet can be pretensioned to over 70% of its tensile strength without being impregnated with adhesive. All these make such material suitable to be prestressed for strengthening concrete structures. Based on the experiments and theoretical studies, a comprehensive strengthening method with prestressed PBO sheet is established including concept, working principle and corresponding countermeasures, whose strengthening effect is validated by both laboratory and field experiments.
Keywords
fiber reinforced polymers (FRP) ; PBO fiber sheet ; retrofit/repair ; bond ; prestressing ; anchorage
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References
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