If you can’t test it, then you can’t build it. For this reason the Strait Bridge would not be feasible. This is stated in the “definitive” project presented by the Stretto di Messina, the state concessionaire for the construction of the work. The designer writes, in English, that a special machine must be used to carry out resistance tests on the cables that will support the pylons of the Bridge. But there is a problem: as university professor Antonino Risitano explained to Today.it, a similar device suitable for the dimensions of the Bridge simply does not exist. If built, it would have colossal dimensions and would take years just to design. Thus, while Salvini is eager to start construction, the project documents reveal that it will be difficult to respect the timetables, which have already been postponed by 120 days.
The “hidden” papers in the final project of the Strait Bridge
It is precisely the final project that shows that the Bridge would not be feasible. As Professor Risitano, full professor of “Machine Construction”, highlighted to Today.it, the problem is highlighted by the designer himself in a 2011 dossier written in English, unlike the other documents which in the vast majority of cases are in Italian. Let’s read it below, with a premise: the bridge designed for the stable connection between Calabria and Sicily is so large that it develops aerodynamics similar to that of an airplane wing, such as to place enormous tension on the materials, especially on the load-bearing cables.
“To verify the effect of sliding, a fatigue test on the saddle is recommended at the executive design stage,” we read in the document. We asked Stretto di Messina SpA for an account of this document but as of the date of publication of this article we have not yet received a response. It is not the only part of the project to have “readability” problems: some documents had been sent to the Ministry of the Environment with tables full of meaningless characters. However, to an expert eye the data reported are sufficient to raise more than one objection.
The tests to which the designer refers concern “the main cables, the most important. They are the ones that support the pylons”, explains Professor Risitano to Today.it. To be clear, as can be seen in the image below, the cables in question are those anchored to the ground at the ends of the bridge and attached to the two pylons on the respective banks, in Calabria and Sicily.
And these cables are among the numerous records of the bridge over the Strait of Messina. Each cable has a diameter of 1.26 meters, with a length of over 5.3 kilometers between the two anchors. In total the four cables weigh 170,00 tons, about as much as a cruise ship. Something “never seen before”, Risitano tells us.
“The cables of the Bridge? Good for drying clothes”
As we have seen, the designer himself explains that stress tests are needed for the cables. But the reference is not clear: “Someone should explain the content of the document – says Risitano to Today.it – The safety coefficient chosen by the designer cannot be valid for dynamic and oscillating structures such as the bridge over the Strait. It is not acceptable, it would be fine for railway bridges, more massive and stable structures. Theoretically, a drying rack would have the same limit, but the safety implications are different: if the clothes fall, it doesn’t do anything.”
“If just one of the cables gives way, the bridge goes down like a brick,” Professor Risitano explains to Today.it.
The example of the drying rack clarifies why the limits of the safety coefficients are set during design: they serve to establish the extent to which a structure can resist the forces that insist on it. If you put too much weight on the drying rack it breaks: it is because it is designed with too low tolerance thresholds.
So how to do it? And what would be the right threshold to set? “Since the tests indicated by the designer are really difficult to carry out – continues Risitano – we could have adapted, for example, with those carried out on the load-bearing cables of cable cars, which are more severe and have higher safety values, of around four times “.
But why use a lower safety coefficient for the cables of the bridge over the Strait than that of the cable cars? “They claim that for the bridge over the Strait – explains Risitano – it is possible to use the same coefficients as railway bridges, but this is a structure that oscillates, like an airplane wing, so much so that the tests on the deck were carried out in wind tunnel. In the other bridges in the world to which they refer the coefficient is around 3 and consider that the conditions of those bridges have nothing to do with this. The threshold set by the designer for the bridge over the Strait is 1.35. So low it’s funny: the cables have to support the weight of the structure and if just one of them gives way, the bridge goes down like a damn.”
The test machine that doesn’t exist: the bridge over the Strait cannot be built
Like other components of the bridge, the cables must also be tested with appropriate instruments. It is the same designer of the Stretto di Messina who shows what the stress testing machine should look like (image below).
Tests with machines of this type were done in the early 1990s in China and Japan. The problem is that to test a record-breaking work like the bridge over the Strait you need adequate machines, also due to the “unprecedented” dimensions of the cables. And according to the data indicated by the designer and developed by Professor Risitano, the machinery for testing the bridge cables should rest on a steel base in the shape of a parallelepiped no less than 6 meters high, approximately 100 meters long and approximately 60 meters wide , with 15 meter high support elements. To give an idea, the machine would be as tall as a five-story building and as long as a football field.
A machine for testing cables with these dimensions does not exist and for Risitano, who for decades has been involved in building complex machines, “it would take 15 years of study to create one like this from scratch. Furthermore – he underlines – it would take a quantity of ‘unimaginable oil for the pistons and mechanical components. The cylinders alone would be 6 meters high and capable of reproducing 8 hertz oscillations, that is, 8 movements per second.
We asked Stretto di Messina how they intend to carry out these tests and with what machinery, but as of the date of publication of this article we have not received any response.
Antonino Risitano, born in 1944, lives a few hundred meters from the place where the pylon on the Messina bank should be built and is not among those against the bridge over the Strait, on the contrary: “I would like to have a work of this type – he tells us – but the current project, in light of the scientific knowledge of our time, is not technically feasible. The work must be done safely and reliably because it must last over time. For example, the Morandi bridge was safe but not reliable.” The solution? “Changing the design and cables,” says Risitano.
But the times? The managing director of the Strait of Messina, Pietro Ciucci, has already asked for a 120-day extension to resolve the critical issues reported by the Ministry of the Environment. Matteo Salvini said he wanted to lay the first stone in the summer of 2024. According to the professor, he has a better chance of building the cable testing machine than a bridge over the Strait of Messina. And the machine we are talking about, as mentioned, has never existed before.
