Bridge reinforcement design.
The structure built in 1973 is a pre-stressed concrete box girder type built by successive cantilevering. It comprises 3 spans that are 56.65 - 95.68 - 56.65 m in length. The balance beams consist of prefabricated voussoirs 2.08 or 3.12 m in length.
The following distress observations were made:
- Insufficient longitudinal pre-stress, under-dimensioned given the creep effects of the concrete and the thermal gradient, which is the main cause of the substantial deflection observed mid-span.
- Insufficient transverse reinforcement in the lower hollow-core slab in the middle of the central span which is the cause of longitudinal cracking and “fishbone” cracking.
- Overall insufficient reinforcement bars against shearing force in the cores and transverse reinforcements in the lower hollow-core slab.
The working designs and works made it possible to implement the following repair actions:
- Horizontal pre-stressing by pre-stress bars passing either side of the lower hollow-core slab.
- Carbon fibre fabric on the outer and inner faces of the box girder to reinforce the cores
- Additional longitudinal exterior pre-stressing with addition of anchoring masses anchored to the existing structure.