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Bending Performance of Masonry Walls Strengthened With Near-Surface Mounted FRP Bars.


pdf icon Bending Performance of Masonry Walls Strengthened With Near-Surface Mounted FRP Bars. (838 K)
Bajpai, K.; Kuthinh, D.

North American Masonry Conference, 9th. Proceedings. June 1-4, 2003, Clemson, SC, 1052-1063 pp, 2003.

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Website: http://www.masonrysociety.org

Keywords:

walls; masonry; literature review; epoxies; mechanical properties; adhesives; concretes; tests; deflection

Abstract:

Unreinforced masonry (URM) buildings constitute an important part of the building stock, and are vulnerable to earthquakes. Retrofitting of existing masonry walls with near surface mounted, non-corrosive fiber-reinforced polymer (FRP) bars, is an attractive option. Previous research has shown that it is difficult to develop the full tensile strength of the bars, which are attached with epoxy in grooves pre-cut in the masonry and mortar joints. In this study, epoxy strengthened with short glass fibers allows close to full strength development of 6.5 mm (114 in) diameter glass FRP bars in 185 mm (7.3 in), or less than half a concrete masonry unit length. This fiber-reinforced epoxy should be effective for other types of bars as well. With full anchorage assured, FRP bars provide an efficient method of strengthening masonry walls against out-of-plane bending. Three narrow (2.85 m x 0.40 m x 0.20 m or 112 in x 16 in x 8 in), grouted, concrete masonry beams reinforced to 45% of balanced ratio and four wide (2.85 m x 0.80 m x 0.20 m or 112 in x 32 in x 8 in) beams reinforced to 66% of balanced ratio were tested in four-point bending. All seven beams exhibited consistent flexural behavior, with ultimate failure precipitated by tensile rupture of the reinforcement at an average ratio of span to maximum deflection of 42. The ACI (530-02) equations predict the flexural strength of these FRP externally reinforced concrete masonry beams conservatively, with a mean ratio of measured to predicted strength of 1.37 and a coefficient of variation of 0.057. There was no difference in behavior between reinforcement parallel or perpendicular to the mortar bed joints. The unexpected shear failure of one FRP reinforced, ungrouted beam needs further investigation.