precompress the tension foundation, are ce- mented into steel tubes, which are themselves cemented into individual hole bored through the limestone The barettes and cables are permanently equipped with measuring devices. The mea- surement of the frequency of a stressed wire in each barrette allows the strain to be deter- mined over time. Load cells under the anchor head of the cables indicated the force. The main tension plates of the superstructure are
anchored on a hammer head, which applies a compression force to the back of the concrete ground beams. The hammer head is the first part of the steel superstructure to be delivered to site, for the concrete substructure to be cast around it. The jacks, at the steel/concrete in- terface, can fine tune the altitude of the centre of the bridge, compensating the slight move- ment of the foundations and the fabrication tolerances.
The two types of foundation are both made up of concrete barettes of rectangular cross sec- tion. A compact milling machines was used because of the poor bearing capacity and the narrow access to the lower quay level. The cut passed through the alluvion down into the top of the strong limestone horizon. The cut was stabilised with thixotropic bentonite mud. The steel reinforcing cages are lowered into the mud and the concrete placed though a tube to the the bottom. The steel cables which
on site review 17
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