DRAGADOS has built the new bridge in Cádiz Bay, according to the project of Carlos Fernández Casado Office. The length is 1180 m, distributed in 120-200-540-200-120 [m] spans. The deck is a steel box girder of 34 m wide and 2.80 m depth including the upper concrete slab.
A typical set up phase consists of: firstly, lifting a steel segment 20 m length by an auxiliary steel heavy lifting device which is situated on the already built deck end; secondly, binding the hoisted segment to the deck by welding; thirdly, tightening the deck strands; then, concreting the voussoir; and lastly, ,moving the truck to the end of the cantilever. Naturally, there are a lot of different possibilities depending on the deck characteristics and on other distinctive features.
The weight of the auxiliary steel heavy lifting device is 4500 kN, the normal weight of the 20x34 meters segments plus the lifting tools is 4000 kN.
Keeping in mind the eccentricity with which the auxiliary steel heavy lifting device takes the segment, the applied loads by the front support of the auxiliary steel heavy lifting device on the last segment is 12,000 kN. These loads are applied in two points and produce important deformations in the section which has to be welded to the lifted segment.
INES Engineers worked with the DRAGADOS Technical Office to analyze the differential deformations between the segments when they joint together and to design measures that would reduce these deformations until a compatible level with the required accuracy of the welding.
The obtained deformations initially reached 60 mm. Three types of corrective measures were designed:
- Global and local stiffening of the sections.
- Adaption of the construction sequence (concrete placement, pre-stressing, etc.).
- Loading up the lifting system, which have been provisionally joined with the vous¬soirs by bolted connections.
- Forces applied by jacks under supports of the auxiliary steel heavy lifting device.
The use of these measures reduces the relative deformations below 5 mm, in all situations and below 2 mm, in their majority.