Erection of a bridge deck for a cable stayed bridge

Autor: prof. ing. Popa Elena – Carmen
Colegiul Tehnic “Anghel Saligny” Bacău

The choice of the construction method depends mostly of the location of the bridge and its surroundings. Studying the ground conditions of our case, suitable method can be chosen, trying to minimize the costs and the time needed.
In fact, as it can be seen from figure 1, we have mostly ground and a very low level of the water on the left of the first pylon. Thus, there, the use of temporary supports could be economically viable.
Instead, for what regards the other two spans, the level of the water is higher, thus, building provisional support could be expensive and consequently a cantilever method would be preferable.
Therefore the proposed solution will be:
1. Construction of the pylons by climbing formwork.
2. Building of the deck on the left of the first pylon, by temporary support and construction of the deck on the right pylon with the cantilever method.
3. Building of the other part of the deck in the mid span.
4. The construction goes on until the deck is completed.

fig1Figure 1: Chosen construction process

This solution limits the necessity of using a boat, which could be expensive. Temporary= supports can be used where conditions are favorable.
Finally, during the construction process, there must be continuous measurements of the forces and the displacements, since there could be errors during the analysis of them; considering that the structure is not complete, even a small error could give rise to a very large unexpected efect.
Specific attention should be given to the cable force, since its value has to be calculated very carefully; otherwise if there are mistakes, there will be problems for a wrong elevation of the deck. A variation of the cable force could come from variation of the length of the cable due to changing in the temperature. Hence by using survey engineering devices this aspect has to be checked.