Analysis of RC beams strengthened with mechanically fastened FRP (MF-FRP) strips

The analytical model for reinforced concrete beams strengthened using mechanically-fastened fiber reinforced polymer (MF-FRP) pultruded strips is discussed in this paper. In this method, FRP strips, reinforced with a combination of carbon and E-glass unidirectional fibers and continuous strand mats, are fastened to the concrete with steel powder-actuated (PA) fasteners and expansion anchors (EA). The model predicts the ultimate strength and failure modes of MF-FRP strengthened beams and was developed based on results of tests on over 75 RC beams of many different sizes using the MF-FRP method, that have been conducted over the last five years. These tests have explored numerous different failure modes and factors affecting the behavior of MF-FRP strengthened beams. The analytical model can be used to proportion the strengthening system for an RC beam so as to cause the beam to fail in a unique ductile failure mode. This procedure was used to proportion strengthening systems for large-scale beams (7.3 m long by 51 cm × 51 cm) that were used to verify the analytical procedure. The strengthened RC beams were designed to fail in a ductile manner. In the test results presented in this paper, the strengthened beams showed increases in yield and ultimate moments of up to 25% and 58%, respectively over an unstrengthened beam. All strengthened beams failed, as intended, in a ductile manner with the ultimate failure mode due to concrete compression failure at large deflections with the FRP strip still firmly attached. Comparisons between the analytical predictions and the experimental results show good agreement.