Recently, DSI was awarded a contract to strengthen an existing steel girder bridge that crosses the Capivari Water Reservoir in southern Brazil. The bridge forms part of the BR-116 connecting road that leads from Curitiba, the capital of the federal state of Paraná, further north towards São Paulo.
The existing bridge was re-built in 2006 after it had collapsed one year ago. Since the bridge was built on unstable ground, settlements occurred that caused the bridge pier to sink into the soil by approximately 40 cm so that the bridge was once again in danger of collapse.
As a permanent solution, the decision was made to build a reinforced concrete frame below the existing bridge. This bracing structure consists of two longitudinal girders, two transverse girders around the caved pier, an H-shaped pylon and two concrete abutments on the opposite side of the river to anchor the back span stay cables.
The support frame is suspended from four approximately 55 m long stay cables that are anchored at the pylon. The support structure accommodates the weight of the existing bridge so that the damaged pier of the existing structure could be removed.
Tricky part was to determine the exact force
The tricky part of this job was to determine the exact force that had to be applied to the stay cables. The force had to be sufficient to lift the old bridge deck without overstressing it. Furthermore, all of the strands in each of the stay cables needed to have the same stress level. This was achieved by dividing the stressing process into five steps, an accurate estimation of the existing loads that had to be lifted and the precise functioning of the stressing method.
In addition to the stay cables, the companies Protendidos DYWIDAG and DSI Prepron also supplied, installed, stressed and grouted the post-tensioning systems that were used in the pylon and the strand post-tensioning systems for the transverse girders of the new structure.