Innovative CFRP-Prestressing System for Strengthening Metallic Structures

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An innovative retrofit system to prestress carbon fiber reinforced polymer (CFRP) plates and attach them to existing metallic beams was developed (patent number CH 706 630 B1) and tested. The system does not require any glue between the CFRP plates and the beams; therefore, surface preparation is not necessary, which reduces the time and cost of retrofitting. The proposed prestressed unbonded reinforcement (PUR) system includes a pair of mechanical clamps that function based on friction. Each clamp can simultaneously hold and attach three CFRP plates to the beam. The design considerations of the clamps, which are the most important elements of the PUR system, were explained. The system has a trapezoidal configuration that offers an easy on-site installation and uninstallation procedures without residual damage on the metallic beam. Three 5-m-long steel beams were statically tested until failure, including one reference unstrengthened beam and two beams that were strengthened with 15% and 31% CFRP prestress levels. A considerable increase in the yielding and ultimate load capacities of the retrofitted beams was achieved. The ultimate load-carrying capacity of the strengthened beams with 15% and 31% CFRP prestress levels increased by more than 23% and 31%, respectively, compared to that of the reference specimen. A finite-element (FE) model was created to simulate the behavior of the retrofitted beams. Next, the FE results were compared with those from the experiments.