A viaduct - is it a bridge or not?

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Bridges, overpasses, overpasses, viaducts - all these words are synonyms. Moreover, they designate very similar construction objects, widely used by man in his economic activity. To distinguish between these concepts, this little material is offered.

Bridge

This is an engineering structure, invented a long time ago. One of the oldest dates back to the thirteenth century BC. Since ancient times, people began to build bridges to overcome water barriers such as rivers, lakes, swamps, etc. Therefore, the word is not only the most used among those proposed, but also the oldest. In a broad sense, all the other structures mentioned are bridges, so the question posed in the title of the article should be answered "yes". However, there is a "but". More on him later.

Overpass

This is a structure that is being built over another road, but is no longer called a bridge, since technologically there are quite serious differences from it. First of all, they are caused by the fact that when designing an overpass, there is no need to take into account the influence of various natural phenomena associated with the watercourse under the bridge. Therefore, the principle of creating supports in this case is fundamentally different. We will not go into technical details, we will recall only three factors that bridge designers have a headache about. This is ice drift, erosion and bulk of ships passing under them. An overpass is, in fact, a bridge over an ordinary road. Therefore, we have another term for this structure. This is the small “but” in the legitimacy of using the word “bridge” when defining an overpass.

Overpass

While the construction of an overpass usually requires two to four spans of 10-30 meters each, the laying of an overpass usually requires more of them. In fact, this is the whole difference between these engineering structures. However, the important point here is that the flyover can cross several types of obstacles at once, for example, it can be a river, a highway and railways at the same time, thus combining both a bridge and an overpass.

Viaduct

Consider the following type of bridge. There is one more type of obstacles, fundamentally different from those already considered by us earlier. This should include ravines, gorges, hollows. Therefore, the word "overpass" can no longer be used here. This is another type of bridge structure - a viaduct. Consider its features.

Construction of viaducts instead of conventional roads is justified in cases where it is not economically feasible to create an embankment. That is, everything is determined by the depth of the ravine, as well as its length in the profile of the available transporthighways.

Thus, the difference between a viaduct and an overpass will be the absence of a more or less even surface under the bridge. Due to this factor, the uniformity of supports and spans in this case is no longer suitable. Viaducts are usually very beautiful and majestic structures. For example, the height of one of the pillars of the highest Millau Viaduct in the world is about 340 meters.

Continuing the topic, we can mention another interesting structure, although it has only a distant relation to such concepts as overpasses, roads. These are the so-called aqueducts. This is analogous to a viaduct, only to carry water, not vehicles, over the same ravine, river or other obstacle, usually part of an irrigation system.

Conclusion

Returning to the question posed in the title of the article, let's finally answer it. Yes, an overpass is a bridge according to the principle of construction, and no, since it is created not over water barriers, but over a similar road surface. Such is the dialectic.