Fiber-Reinforced Polymer Retrofitting of Rectangular Reinforced Concrete Columns with or without Corrosion

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Title: Fiber-Reinforced Polymer Retrofitting of Rectangular Reinforced Concrete Columns with or without Corrosion

Author(s): Stathis N. Bousias, Thanasis C. Triantafillou, Michael N. Fardis, Loukas Spathis, and Bill A. O’Regan

Publication: Structural Journal

Volume: 101

Issue: 4

Appears on pages(s): 512-520

Keywords: column; corrosion; fiber-reinforced concrete; polymers; seismic; strength; test

Date: 7/1/2004

Abstract:
Twenty concrete columns, with a 250 x 500 mm section and materials and detailing emulating older construction, are tested to investigate, in a systematic way, the effect of important parameters of seismic retrofit with fiber-reinforced polymer (FRP) wraps, as well as the effect of reinforcing bar corrosion on the effectiveness of the retrofitting. As far as the number of FRP layers and the fiber material is concerned, it is concluded that replacing carbon fibers by glass fibers, while maintaining the same extensional stiffness of the FRP jacket in the circumferential direction, leads to about the same performance. Nonetheless, FRP extensional stiffness seems to be the controlling factor up to a certain limit, as increasing the number of carbon fiber-reinforced polymer (CFRP) layers from two to five does not materially improve performance. Previous damage left unrepaired reduces the effectiveness of rehabilitation with FRP wraps. Confinement by the FRP is very effective in increasing concrete strain capacity to levels of 5 to 6% even in the middle of a wide side of the column. Nonetheless, rectangular columns tested in the strong direction (with a 250 mm-wide compression zone) are found to benefit more from FRP wrapping than when tested in their weak direction (with a 500 mm-wide compression zone). Although wrapping with FRP is found to significantly improve seismic performance of columns that suffer from both lack of seismic detailing and of corrosion of the reinforcement, such corrosion materially reduces the effectiveness of FRP wraps as a strengthening measure, as the corroded bars become the weak link of the column, instead of the confined compression zone.