The image of bridges raised is often used in poetry as a symbol of irresistible forces that prevent lovers from being together. In life, the opening of bridges takes place at a strictly allotted time and has no romantic reasons.
Most of the rivers on which the largest cities in the world are built are navigable, so there is only one reason for the opening of the bridges, namely, to allow large water transport to pass along the river over which the bridge is erected and not to touch the deck part of the spans and bridge structures. ships could freely pass along the river; several types of drawbridges were invented. For example, there are bridges consisting of three parts, the middle part of which rises on supports strictly vertically. Another option for a three-segment bridge is a flooded center bridge. The most familiar to us drawbridges are called swing bridges. Drawbridges of St. Petersburg are the hallmark of the city and are built exactly according to the type of swinging structures. Many excursion programs are designed in such a way that tourists can watch the process of drawing bridges after sunset. They are bred for three hours - from 1.30 to 4.30. However, it is important to remember that bridges in St. Petersburg are only raised during the navigation period - from April 20 to November 10. However, St. Petersburg is far from the only city in the Russian Federation where drawbridges have been built. In Rostov-on-Don, the railway bridge has a lifting middle part, in Kaliningrad there is a bridge over the Pregolya River with a vertical swing system, it is used for road and rail traffic. In Belomorsk, a movable railway bridge has been laid across the Belomorkanal. In Europe, bridges with movable mechanisms are also used, it is enough to recall the famous Tower Bridge. And in Copenhagen, for example, there is a bridge that can be raised by yacht managers on their own, if the vessel needs to go along the river. There are also drawbridges in Antwerp, Bruges, Amsterdam, Ghent, Dunkirk.
