Strengthening and repair works of a R.C. bridge over Arno River

The paper deals with the strengthening and repair works of a reinforced concrete bridge over Arno River at Levane (Arezzo), in Italy. The bridge, built in 1959, is formed by a three span Gerber beam (17.55 m – 28.30 m – 17.55 m). In 1996 experimental tests and numerical analyses have put into evidence the inadequate bearing capacity of the bridge for both the first and the second class road loads prescribed by the Italian Bridge Code. Therefore a strengthening design has been developed to upgrade the structure to a First Class bridge. The works were performed from September 1999 to September 2000 and concerned the main structural elements: the longitudinal and transversal beams, the upper slab, the Gerber hinges, the right abutment, and the foundations. The flexural capacity of the longitudinal beams was increased using external unbonded tendons, while at the supports their shear capacity was increased applying composite fabrics made of carbon fibres. The upper slab was thickened with an additional layer of no shrinkage mortar, connected to the existing slab with steel bolts, and new transversal steel beams were installed at the intradox of the slab to reduce its span. In the past urgent works have been done on the foundations of the right abutment, which, under the scour action of the water currents, has exhibited an inward rotation. Additional works were performed on the right abutment, installing sub-horizontal anchors, and on the foundations of the piers and left abutment. In the first part of the paper the main phases of the works are described, while in the second part the results of the experimental tests on the strengthened bridge are presented. The structural performance of the strengthened bridge was significantly improved, as the thickening of the upper slab and the external prestressing increased the flexural stiffness of about 20 %.