Strand Stay Cables Stabilize Capivari Bridge

Context

The existing bridge was re-built in 2006 after it collapsed in 2005. Since the bridge was built on unstable ground, settlements occurred that caused the bridge pier to sink into the soil by approximately 40cm 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.

Solution

The support frame is suspended from 4 approximately 55m long, Type DG-P109 Dyna Grip 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.

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 DYWIDAG Dyna Grip Stay Cables needed to have the same stress level. This was achieved by dividing the stressing process into 5 steps, an accurate estimation of the existing loads that had to be lifted and the precise functioning of the ConTen stressing method developed by DYWIDAG.

In addition to the DYWIDAG Dyna Grip Stay Cables, the DYWIDAG companies Protendidos DYWIDAG and DSI Prepron also supplied, installed, stressed and grouted the 32 and 36mm Ø DYWIDAG Bar Post-Tensioning Systems that were used in the pylon and the strand post-tensioning systems for the transverse girders of the new structure.

This special application is a milestone and a first reference for DYWIDAG for stay cable systems in Brazil. Furthermore, DSI Prepron successfully acted as a subcontractor for stay cable systems for the first time in this project.