Bridges are an inalienable 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.
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 being built in megacities for movement above roads, forming large interchanges. The main details of their design are spans and supports.
Types of bridges can be classified according to several criteria:
Since the man threw a tree from onethe banks of the river to get to the other, it was a long time and a lot of effort was put into 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 a tree. 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 farms form part of a separateconstruction, 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. 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 -arch-cantilever bridge, where the two semi-arches are connected at the top and resemble the letter "T". Arched construction 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 thiscase - 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 condition, the pylons are mounted on opposite banks, between them 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 entire bridge structure, 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 andconnection 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 barriers. They are dangerous in the period of strong waves on the water, impede navigation, and movement on them has limitations for multi-ton trucks.
Most modern bridges involveThe 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:
Metal constructions have advantages,consisting in the simplicity of collection, so almost all types of railway bridges are built from this material. Metal parts are manufactured industrially at the factory, while the size can be adjusted. Depending on the load-carrying capacity of the mechanisms by which the installation will be carried out, the factory blanks of the future one-piece connection are formed.
Weld the design of the parts can bedirectly at the final installation site. 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 tons, can easily carry and hoist an all-metal span over the supports.
As a material for the construction of bridgesIron 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.
When building railway bridges, a widethe use of metal structures with lattice trusses. The main advantage of these solutions is the efficiency in operation, the speed of construction and dismantling of individual parts, a relatively low cost of production, the possibility of constructing the structure in the shortest time possible in accessible areas and in any geographical area.
The first bridges in the history of mankind were builtmade of wood. For a long time these structures could not be used without proper repair, constant preventive maintenance and replacement of individual 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:
The beam structure is the simplest, and thereforequickly erected building. Support beams are hammered into the ground to a depth of 4 m. At the upper 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 was a tendency of revivalthe 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.
In St. Petersburg there are 93 waterways,This includes rivers, canals, canals and almost 100 water bodies. Unimpeded communication between the islands and parts of the city provides 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 are so actively used by divorce crossings, as in St. Petersburg.
The symbol of the Northern capital is considered to be oneof the oldest bridges - Palace. It was built on the design of the engineer AP Pshenitsky and connects the Admiralty Island with the Spit of the Vasilyevsky Island. Modern mechanisms raise the 700-ton construction of the central span for passage of vessels.
The longest drawbridge in St. Petersburgbears the name of Alexander Nevsky. Its length is 905.7 m, the central spreading span is made of metal, the time of building the construction is only 2 minutes.
Types of bridges in St. Petersburg include allthe history of bridge construction - from the first wooden to modern multi-band cable-stayed structures. The Bolshoi Obuhovsky 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.
In St. Petersburg in the abundance of various speciesbridges, there are also ancient ones that have become symbols of a bygone era, but their purpose has not changed, although it has acquired a fleur of stories and romance. So, the Potseluy Bridge across the Moika River attracts tourists with its name, but it happened from the name of the 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, andthe 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 appease the "bloody" boulder, some townspeople throw coins from the bridge to the Neva and pour red wine. Also, many argue that on Liteiny you can meet the specter of Lenin.
While the bridge across the Kerch Strait has not been built, the five large crossings look like this:
