Ponte Morandi - Analisi di un delitto

The homogeneous reinforced concrete bridge



"It has been agreed to call a cable-stayed bridge a system that is resistant to straight girder constrained on supports, partly conceptually rigid (shoulders and stacks) and partly to behaviour noticeably different from the previous ones, IE- characterised by the value of their elastic constant comparably much less , because they consist of the ends of oblique stays (the stays) passing through the upper ends of vertical antennas placed in correspondence with the supports mentioned above. "



Detail of the connection of the stays of the Morandi bridge



This is the definition given by Riccardo Morandi to this type of bridges, which are not only pleasing on the aesthetic side, but, compared to the suspension bridge, are more convenient in the light field between 200 m and 1100 m, especially if it is planned railway transit. In fact, the cable-stayed bridge with respect to the suspension bridge is less deform-able, and more easily constructed and involves a decidedly lower amount of steel (for cables).



In fact, Morandi wrote: "such a resistant system offers a series of interesting features that make it suitable for the construction of large bridges of reinforced concrete, essentially due to the fact that the component of the reaction of oblique rods, passing through the central bari surface horizontal of the girder, balanced for each load arrangement symmetrical with respect to the transverse plane passing through the axis of the general pile, determines a compression stress (variable when varying the random loads on the girder itself) which produces a strong reduction of the tensile stresses of it, with a consequent saving of metal armour".



Why HOMOGENOUS STRUCTURES



Morandi then continues with some calculations on the topics of loads and actions, and on the idea of ​​protecting steel cables with pre-stressed concrete sheaths. And in this sense he explains why he used the term HOMOGENIZED: "the conceptual elimination of cracks in the concrete of the sheaths ensures an effective protection of steel from atmospheric agents. The tie rods, therefore, at least in the operating conditions, behave like long and thin concrete beams, pre-compressed and stressed essentially to decompression when the loads pass, therefore the system, with all its members, will have a comparable behaviour and can be considered homogeneous. This is the reason why it was considered to define such HOMOGENIZED STRUCTIVE BRIDGES.