The flyover is a curved continuous prestressed concrete bridge deck, spanning 54.21 +48.68 +49.85+ 35.37m, with a total length of 188.110 m. Its cross section is a tricellular box beam, 10m wide and 2.25m depth, without cantilevers, having a very important torsion resistant area in order to diminish the tangential stresses due to torsion moments.
The deck is torsion fixed in both ends being its intermediate supports cylindrical columns, 1.80 m in diameter, that support the deck by means of one unique pot bearing. So, the torsion span is the total length of the deck, and the torsion moments accumulate up to the abutments.
These are designed as closed walls and must transfer to the foundations not only the vertical and longitudinal reactions but also the transversal reactions due to centrifugal and wind and the important torsion moments due to curvature in plant and the punctual supports on piers
An interesting decision has been taken about the conception of the bearing devices. Due to the importance of the vertical reactions and the displacements that must been allowed, POT bearing devices has been selected. With this kind of bearings, the longitudinal structural scheme of the deck is: fixed to one abutment while free in the other supports.
Normally when curved continuous prestressed concrete bridges are not very long the POT bearings are placed with its guide oriented according to the direction of the vector radius that joints the fixed bearing with the corresponding pier axis. This solution diminishes the horizontal forces on piers due to horizontal imposed deformations, meanwhile only prestressed action produces internal forces. The problem is that, in the free end of the deck, the displacement is not tangential to the curve but, for little displacements, the transversal component of displacement can be absorbed by a neoprene superficial dilatation joint without any disturbance.
In this case, we have prioritized the functional conditions: as the deck is very long and it will have big displacements at the free end, we have preferred to guide these displacements of the dilatation joint parallel to the curve, without any transversal component, so any type of dilatation joint for long displacements can be placed. That means to place the guides of all the POT bearings oriented in parallel way to the curve.
From a structural point of view, this solution releases the internal forces due to prestressing but the piers must resist then the effects of actions due to temperature and shrinkage. Piers have larger internal forces but this solution presents the advantage that POT bearing guides controls very well the transversal buckling of piers
The final design follows the above mentioned criteria. A longitudinal fixed POT bearing is located at the end of the deck on abutment 1 and the guide of all the POT longitudinally free bearings is oriented according to the tangent to the curve at each support.