ABSTRACT
A number of experimental investigations on fibre reinforced polymer (FRP) are available in the literature but very few information is available on specimens strengthened with pretensioned FRP laminates. An experimental study on real-scale RC and PRC beams strengthened in flexure with FRP laminates, developed at the University of Padova, Italy, together with a related case study is described in this work. Externally bonded FRP reinforcement was applied in different ways with different types of end-anchorage devices and, in some beams, pre-stress transfer. After characterization of the single materials, four-point bending tests were executed and crack pattern and failure modes were studied.
This FRP pretensioning technique was applied for strengthening the girders of the viaducts on A14 Highway Bologna-Taranto, Italy. The bridges had about 40 years and showed structural problems due to concrete deterioration and significant increase of traffic weight. The intervention has regarded both main longitudinal and transversal beams.
In this paper, firstly the results of experimental testing of real-scale RC and PRC beams strengthened in flexure with ordinary and pre-tensioned FRP laminates are given and then a practical application of the same FRP pretensioning technique for strengthening of the girders of the Battiferro – Navile viaduct (A14 Highway Bologna-Taranto, Italy) is shown.
Five real-scale beams (four RC beams and one PRC beam with pre-tensioned internal strands) 10 m long, of cross-section 300 × 500 mm, were tested.
Failure of PRC prestressed beams was due to delamination of the CFRP, but prestressing and end-anchorage action delayed complete failure. A relevant increment in the ultimate load and an increment of the load at which the first crack appeared occurred for beams with pretensioned laminates with respect to the control beam, due to the compressive axial force transferred by pretensioning and, for concrete prestressed beam, also by internal strands.
The technology of strengthening with pretensioned FRP laminates was then applied to a real case study, namely on the girders of the Battiferro-Navile viaduct in Bologna, here reported and others in Senigallia (A14 Highway Bologna-Taranto, Italy). This bridge was about 40 years old and showed structural problems due to concrete deterioration and also significant increase of traffic loads. The intervention has regarded both main longitudinal PRC beams and transversal RC beams.
The CFRP pre-tensioning system has resulted capable of increasing the ultimate capacity of the structural element and load at which first cracking occurs. Furthermore it allows reduction of crack amplitudes, more uniform distribution of cracks and better utilization of CFRP material characteristics with strain values near the ultimate.
