Prestressed Box Girder Bridge Strengthened by an Internal Tubular Arch

Since its completion in 1976, Osstrupen Bridge in Norway has sagged about 250 mm beyond its original precamber at the midspan hinge. Since the general state of the bridge is good, a solution was sought for raising the girder back to its target configuration while also strengthening it. It was determined to add an internal arch composed of two parallel tubes, hidden in the box and continuous at the center. The tubes are jacked at both ends and the uplifting forces are transferred to the girder through interconnections composed of trusses, which also prevent the tubes from buckling. Two alternative materials were considered for the tubes: high-strength steel and carbon fiber reinforced polymer (CFRP). The paper presents the mechanical response of the two types of coupled systems during jacking operations, under service loads, and when subjected to temperature variations. CFRP has the advantages of a low weight and a low coefficient of thermal expansion, giving a somewhat higher uplift and stress relief to the girder, as well as lower deflection due to ambient temperature variations. Both choices of material were shown to work well and to possess sufficient buckling resistance. For the bridge, a nearly full recovery of the sag at the hinge can be expected, with the extra weight of a new wearing course being accounted for. After rehabilitation, the bridge will carry heavier vehicles than it was originally designed for.