Flexural strengthening of continuous concrete beams using external prestressed steel bars

A full-scale experimental study was undertaken to observe and assess the behavior of continuous concrete beams with external prestressed bars. Three beams - a control beam and two comparable beams strengthened using external prestressed bars - were tested in two-point loading of the interior span of three continuous spans. The diameters of the external prestressed bars were 18 and 22 mm (0.71 and 0.87 in.), respectively. For the strengthened beams, V-shaped profiles were used with a deviator located at the middle bottom of the interior span, and the effective prestress was 45% of the yield strength of the external steel bars. Test results indicate that the external prestressing increased the load-carrying capacity by about 25% and the flexural stiffness by about 15%. An analytical model developed by the authors was applied that uses the beam collapse mechanism, plastic hinge length, and deformation of external bars depending on the beam deformation at the deviator point. Predictions of the nominal strength and the corresponding external bar stress compared closely to the test results.