Bridges are an essential attribute of almost every river, they help overcome obstacles, thanks to them the distances become smaller, and getting from point "A" to point "B" is more comfortable and faster. With the advent of new materials and technologies, complex cross-over structures become a reality.
What is a bridge
Bridges are the continuation of the road through an obstacle. Most often they are paved through a water obstacle, but they can also connect the edges of a ravine or canal. In connection with the development of transport infrastructure, bridges are built in megacities for movement above roads, forming large interchanges. The main details of their design are spans and supports.
Classification of bridge structures
Types of bridges can be classified according to several criteria:
- For the main purpose of use;
- Constructive solution;
- Building materials;
- Depending on the length;
- By the term of operation;
- Depending on the operating principle.
Since the man threw a tree from one bank of the river to get to the other, it took a lot of time and a lot of effort in the construction of engineering facilities. As a result, different types of bridge structures appeared. Let us consider them in more detail.
Materials for their construction are steel, its alloys, reinforced concrete, and the first material was wood. The main elements of load-bearing structures of this type are beams, trusses, which transfer the load to the supports of the base of the bridge.
Beams and trusses form part of a separate structure, called the "span". Spans can be split, cantilevered and continuous, depending on the connection scheme with the supports. The first of them have two supports from each edge, continuous can have a larger number of supports, depending on the need, and at the console bridge the flights go beyond the anchor points, where they connect with the subsequent flights.
For their manufacture, steel, cast iron, reinforced concrete castings or blocks are used. The first materials for the construction of this type of bridges were stones, cobblestones or monolithic blocks composed of them.
The basis of the design is the arch (arch). The joining of several arches by road or rail is an arch bridge. The roadway can have two locations: above the structure or below it.
One of the varieties is a hybrid - an arched-cantilever bridge, where the two semi-arches are connected at the top and resemble the letter "T". The arched structure can consist of one span, and then the main load falls on the extreme supports. If the bridge consists of several connected structures, then the load is distributed to all intermediate and extreme supports.
The main materials for construction in this case are steel, reinforced concrete. The structures are erected in places where it is impossible to install intermediate supports. The supporting element is pylons connected by cables. To keep the bridge in a stable condition, the pylons are mounted on opposite banks, between them they stretch the cable connection to the ground, where it is securely fixed. Towards the outstretched horizontal cables are fastened vertical, also joining the chains that will support the canvas of the bridge. Stiffness of the canvas attached beams and trusses.
Building materials - steel, reinforced concrete. Like the suspension analogues, their design involves pylons and cables. The difference is that the cable joint is the only one that connects the structure of the entire bridge, ie the cables are not attached to horizontally stretched carriers, but directly to the end supports, which makes the structure more rigid.
"Floating" ferries do not have a rigid skeleton and connection with the shore. Their construction is assembled from separate sections with a movable connection. A variety of this type of bridges are flooding crossings. Most often they are temporary structures, which are used until the moment when ice is established on water obstacles. They are dangerous in the period of strong waves on the water, make navigation difficult, and movement along them has limitations for multi-ton trucks.
Most of the modern bridges involve the use of metal in the bearing parts of structures. For a long time, the metal bridge was considered to be the most durable type of structure. To date, this material is important, but not the only component of bridge connections.
Types of metal bridges:
- Arched constructions.
- Viaducts with spans.
- Hanging, cable-stayed.
- Overpasses with reinforced concrete supports, where spans are mounted from metal joints.
Metal structures have the advantages of simple collection, so almost all types of railway bridges are built from this material. Metal parts are manufactured in an industrial way in the factory, while the size can be adjusted. Depending on the load-carrying capacity of the mechanisms with which the installation will be carried out, the factory blanks of the future one-piece connection are formed.
Weld the design of the parts directly on the site of the final installation. And if earlier it was necessary to connect a multitude of parts of a single span, now a crane with a lifting capacity of 3600 t can easily carry and hoist an all-metal span over the supports.
Advantages of metal structures
As a material for the construction of bridges, iron is rarely used because of its poor resistance to corrosion. High-strength steel and its compounds have become a demanded material. Its excellent operational qualities can be assessed on such projects as cable-stayed types of bridges, with huge spans. An example is the Moscow Bridge across the Dnieper in Kiev or the Obukhov Bridge in St. Petersburg.
In the construction of railway bridges , metal structures with latticed trusses were widely used. The main advantage of these solutions is the efficiency in operation, the speed of construction and dismantling of individual parts, the relatively low cost of production, the possibility of constructing the structure in the shortest possible time on available sites and in any geographical area.
The first bridges in the history of mankind were built of wood. For a long time these structures could not be used without appropriate repairs, constant preventive works and replacement of separate parts and fastenings. This was associated with the difficulties of construction and the fragility of the material itself. Currently, the following types of wooden bridges are being built:
- Depending on the system - beam, podkosnye.
- Depending on the design - batch structures with spans, truss bridges.
The beam structure is the simplest, and therefore the fastest erected building. Support beams are hammered into the ground to a depth of 4 m. At the top ends of the piles, with the help of steel pins, the nozzles are laid, all the piles are connected in a single whole, the roadbed is laid on top. When building a wooden bridge, it is important to create a strong interface between the structure and the embankment from the ground at both ends, so that the bridge is stable.
Now there is a tendency to revive the construction of wooden bridges, which is associated with the advent of technology for manufacturing glued beams, more resistant to aggressive environments, external torsion forces and more durable in operation, besides its length does not depend on the natural growth of the tree.
Poetics and Practice
In St. Petersburg there are 93 waterways, including rivers, canals, canals and almost 100 water bodies. Unimpeded communication between the islands and parts of the city is provided by bridges, which number about 800, of which 218 are intended for pedestrians. Since the beginning of the construction of the city was laid the tradition of building bridges, without which St. Petersburg is unthinkable. They form part of its architecture, history, traditions and culture.
Perhaps, in none of the cities of Russia so actively use divorce crossings, as in St. Petersburg.
The symbol of the Northern capital is one of the oldest bridges - Dvortsovy. It was built on the project of the engineer AP Pshenitsky and connects the Admiralty Island with the Spit of the Vasilyevsky Island. Modern mechanisms raise 700-ton construction of the central span for passage of vessels.
The longest drawbridge in St. Petersburg is named after Alexander Nevsky. Its length is 905.7 m, the central divergent span is made of metal, the time for the construction of the structure is only 2 minutes.
Types of bridges in St. Petersburg include the entire history of bridge construction - from the first wooden to modern multi-band cable-stayed structures. The Bolshoi Obukhov Bridge, for example, has a length of 2824 m, and today it is one of the longest engineering structures in Russia. It is made up of two parallel identical parts, along which a four - lane one - way movement is organized .
St. Petersburg legends
In St. Petersburg, various types of bridges are represented in abundance, there are also old types that have become symbols of a bygone era, but their purpose has not changed, although it has been covered with a flair of stories and romance. So, Kotseluev Bridge across the Moika River attracts tourists with its name, but it happened from the name of merchant Potseluev, whose drinking house "Kiss" was located next to the ferry, and to romantic impulses, the name has nothing to do.
Interesting legends grew Foundry Bridge, and the dramatic plot arose immediately upon its laying. It is believed that one of the foundation stones was the sacrificial Atakan stone. Now he catches up with longing for passers-by and provokes suicide. To cajole the "bloody" boulder, some townspeople throw coins from the bridge to the Neva and pour red wine. Also, many argue that on Liteiny there is a specter of Lenin.
The five longest bridges in Russia
Until a bridge is built across the Kerch Strait, the five large crossings look like this:
- Russian bridge in Vladivostok. The length of the building is 3100 m, the opening took place in 2012. For the first time about its need to think about in 1939, but carried out at the present stage.
- The bridge in Khabarovsk. Its length is 3891 m. It has two levels. On the lower open the railway traffic, and on the upper - the car. Its image is decorated with a five thousandth note.
- Bridge on the river Yuribey. It is located beyond the Arctic Circle in the Yamal-Nenets Autonomous District. The length of the structure is 2893 m.
- The bridge over the Amur Bay has a length of 5331 m. It was opened in 2012. It is interesting by a lighting system that helps save up to 50% of electricity.
- Presidential bridge across the Volga in Ulyanovsk. Its length is 5825 m. The construction was conducted for 23 years.