Bridges are an integral attribute of almost every river, they help to 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 crossing structures become a reality.
What is a bridge?
Bridges are a continuation of the road through an obstacle. Most often, they are laid through a water barrier, but can also connect the edges of a ravine or channel. In connection with the development of transport infrastructure, bridges are being built in megacities for movement over roads, forming large interchanges. The main details of their design are spans and supports.
Classification of bridge structures
Types of bridges can be qualified according to several criteria:
- for the main purpose of use;
- constructive solution;
- building materials;
- depending on length;
- by term of operation;
- depending on the principle of work.
Since a person threw a tree from one side of the river to get to the other, a lot of time has passed and much effort has been put into the construction of engineering structures. As a result, various types of bridge structures appeared. Let's consider them in more detail.
Beam
The materials for their construction are steel, its alloys, reinforced concrete, and the first material was wood. The main elements of the supporting structures of this type are beams, trusses that transfer the load to the supports of the base of the bridge.
Beams and trusses are part of a separate structure, called the "span". Spans are split, cantilever and continuous, depending on the connection scheme with the supports. The first of them have two supports on each edge, continuous ones can have a larger number of supports, depending on the need, and at the cantilever bridge spans go beyond the reference points where they are connected to subsequent spans.
Arched
For their manufacture, steel, cast iron, reinforced concrete casting or blocks are used. The first materials for the construction of this type of bridge were stones, cobblestones or monolithic blocks made up of them.
The basis of the design is the arch (arch). The connection of several arches by road or rail is an arched bridge. A roadway can have two locations: above or below the structure.
One of the varieties is a hybrid - arch-cantilever bridge, where two semi-arches are connected in the upper part and resemble the letter "T". An 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.
Suspension bridges
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 the pylons connected by cables. To keep the bridge in a stable state, pylons are mounted on opposite banks, between them they stretch a cable connection to the ground, where it is securely fixed. Vertical cables are attached to the extended horizontal cables, also connecting chains that will support the canvas of the bridge. The rigidity of the canvas is given by beams and trusses.
Cable-stayed bridges
Building materials - steel, reinforced concrete. As with suspended analogs, their design involves pylons and cables. The difference is that the cable-stayed connection is the only one that connects the design of the entire bridge, i.e. the cables are attached not to horizontally stretched carriers, but directly to the final supports, which makes the design more rigid.
Pontoon
“Floating” crossings do not have a rigid frame and connection with the coast. Their design is assembled from separate sections with a movable connection. A variation of this type of bridges are flood crossings. Most often they are temporary structures that are used until ice is established on water barriers. They are dangerous during a period of severe unrest on the water, complicate navigation, and movement on them has restrictions for multi-ton trucks.
Metal bridges
Most modern bridges involve the use of metal in the supporting parts of structures. For quite a long time, a metal bridge was considered the most durable type of structure. Today, this material is an important, but not the only component of bridge connections.
Types of metal bridges:
- Arched structures.
- Span viaducts.
- Hanging, cable-stayed.
- Overpasses with supports made of reinforced concrete, where the spans are mounted from metal compounds.
Metal structures have the advantages of ease of assembly, so almost all types of railway bridges are built from this material. Metal parts are manufactured industrially at the factory, and the size can be adjusted. Depending on the carrying capacity of the mechanisms with which the installation will be carried out, factory blanks of the future integral connection are formed.
It is possible to weld a structure from parts directly at the place of final installation. And if earlier it was necessary to connect many parts of one span, now a crane with a lifting capacity of 3600 tons can easily transfer and hoist an all-metal span onto its supports.
Steel Benefits
Iron is rarely used as a material for bridge construction because of its poor corrosion resistance. High-strength steel and its compounds became the demanded material. Its excellent performance can be appreciated on projects such as cable-stayed bridge types, 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 trellised 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 ability to build structures in the shortest possible time on accessible sites and in any geographical area.
Wooden bridges
The first bridges in the history of mankind were built of wood. For a long time, these structures could not be used without proper repair, constant preventive maintenance and replacement of individual parts and fixtures. This was associated with difficulties in construction and the fragility of the material itself. The following types of wooden bridges are currently under construction:
- Depending on the system - beam, strut.
- Depending on the design - package buildings with spans, truss bridges.
The beam structure is the simplest, and therefore quickly mounted structure. The support beams are driven into the ground to a depth of 4 m. Nozzles are laid on the upper ends of the piles with steel pins, all the piles are connected into a single unit, a canvas is laid on top for movement. When constructing a wooden bridge, it is important to create a strong mate between the structure and the embankment from the soil at both ends, this is done 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 the production of glued beams, more resistant to aggressive environments, external torsion forces and more durable in operation, moreover, its length does not depend on the natural growth of the tree.
Poetics and practice
There are 93 water arteries in St. Petersburg, including rivers, canals, canals and almost 100 water bodies. Unhindered communication between the islands and parts of the city is ensured by bridges, of which there are about 800, of which 218 are intended for pedestrians. From the beginning of the construction of the city, the tradition of building bridges was laid, without which St. Petersburg is already unthinkable. They form part of its architecture, history, traditions and culture.
Perhaps in no other city in Russia are they actively using adjustable crossings as in St. Petersburg.
The symbol of the Northern capital is rightfully considered one of the oldest bridges - the Palace. It was built by the project of engineer A. Pshenitsky and connects the Admiralty Island with the Spit of Vasilyevsky Island. Modern mechanisms lift the 700-tonne central span structures for ship passage.
The longest drawbridge in St. Petersburg is named after Alexander Nevsky. Its length is 905.7 m, the central adjustable span is made of metal, the construction dilution time is only 2 minutes.
Types of bridges in St. Petersburg include the entire history of bridge construction - from the first wooden to modern multiband 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 composed of two parallel identical parts, along which a four - way one - way traffic is organized .
St. Petersburg legends
In St. Petersburg, various types of bridges are represented in abundance, there are also ancient ones that became symbols of a bygone era, but their purpose has not changed, although it has grown over with a fleur of stories and romance. So, the Kisses bridge across the Moika River attracts tourists with its name, but it came from the name of the merchant Potseluev, whose drinking house "Kiss" was located next to the crossing, and the name has nothing to do with romantic impulses.
The Liteiny Bridge overgrown with interesting legends, and a dramatic plot arose immediately when it was laid. It is believed that one of the foundation stones of the pillars was the Atakan sacrificial stone. Now he catches up longing for passers-by and provokes suicide. To appease the "bloody" boulder, some citizens throw coins from the Neva River and pour red wine. Also, many argue that at the Foundry you can meet the ghost of Lenin.
The five longest bridges in Russia
Until a bridge across the Kerch Strait has been built, the five large-scale crossings look like this:
- Russian bridge in Vladivostok. The length of the structure is 3100 m, the opening took place in 2012. For the first time, it was thought about its necessity in 1939, but it was implemented at the present stage.
- The bridge in Khabarovsk. Its length is 3891 m. It has two tiers. Railway traffic is open on the lower, and automobile traffic on the upper. His image adorns the five thousandth bill.
- The bridge on the Yuribey River. It is located beyond the Arctic Circle in the Yamalo-Nenets Autonomous District. The length of the structure is 2893 m.
- The bridge across the Amur Bay has a length of 5331 m. It was opened in 2012. It is interesting for its lighting system, which helps save up to 50% of electricity.
- Presidential bridge over the Volga in Ulyanovsk. Its length is 5825 m. Construction was carried out for 23 years.