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07-02-2019 | Posted by Joaquín Martí
It is difficult to talk about bridges purely in engineering terms. Bridges constitute one of the most useful types of man-made structures. They connect what nature separated, they provide cohesion to the territory. Indeed, Principia was named 40 years ago after Newton’s chief work, so it is befitting to quote him: “We build too many walls and not enough bridges”. Clearly, his wisdom extended beyond physics.
That said, bridges are not generally easy to build and some of them are definitely very difficult. First of all, all bridges defy gravity, with their own weight and with the static and dynamic loads that traffic will generate. Then they must accommodate nature: the foundation ground for piers and abutments, plus temperature changes, winds, earthquakes, floods, tides and tsunamis. And then there are accidents, like ship impacts, train derailments, forest fires, and even terrorist bombs. The design of a bridge requires competence in many disciplines.
It would not be very practical to build a full-scale bridge to test whether it works as intended against those loads and that is where simulation comes to the rescue.
Of course, we learn a lot from a failure, much more than from a success, and famous catastrophes like that of the Tacoma Narrows Bridge in 1940 or the very recent one of the Morandi Bridge in Genoa have taught us a lot. But other ways of learning are certainly preferable.
Principia has carried out studies for two dozen bridges. Some of them are very notorious, like the Oresund Crossing between Denmark and Sweden, the 4th Panama bridge over the Panama Canal, the Valdivia bridge in Chile, the bridge across the Danube linking Bulgaria and Rumania, or the new Forth Crossing in Scotland. And we have studied two bridges by Calatrava that, like most of his works, strongly depart from the conventional.
In those projects we investigated an exhaustive list of design conditions. Apart from the more obvious ones imposed by gravity, we have studied vibrations caused by traffic, wind and pedestrians. We have of course analysed earthquake effects in the structure, the foundation and the ground, even accounting for different seismic inputs along long bridges.
We have studied ship impacts on piers and foundations, and designed protection systems. We have analysed the dynamics of the lifting of bridge segments from barges in several bridges. We have investigated the effects of forest fires on bridge piers. And we studied the vulnerability of the King Fahd Causeway to terrorist explosions and the effects of impacts from falling rocks on a pedestrian walkway.
We have also participated in research projects oriented to specific problems, like the behaviour of integral (jointless) bridges for high-speed railways, the demolition by diamond-saw cutting of a prestressed viaduct, or the development of control systems for the vibrations caused by pedestrians.
Most of those studies were conducted in support of the designer. But there are a few instances in which we studied failures that had already taken place: failure of piers, excessive vibration of suspension cables, collapse of support structures, effects of underwater explosions, etc.
Briefly, bridge design is a field that activates many aspects of engineering. With the help of simulation, we are better suited to act on Newton’s advice.