Supports are called the bearing element of the bridge, supporting the spans and transferring the load from them down to the foundation. Such structures should be erected in full compliance with SNiP standards. Bridge supports can be classified according to several criteria.
Main types by manufacturing method
Supports are assembled using technologies that subsequently ensure the maximum reliability of the bridge and its ability to withstand the necessary loads. According to the method of erection, they can be:
- monolithic;
- national teams;
- precast-monolithic.
Installation of monolithic bridge supports is carried out on site by pouring concrete into the formwork. Prefabricated are installed from prefabricated concrete or reinforced concrete elements. At the same time, the latter are connected with exact observance of certain standards. Prefabricated monolithic supports are combined type structures. That is, some of them are poured on the spot, and some are assembled.
Monolithic supports, in turn, can belong to the group of structures:
- lined;
- withoutcladding.
Different materials can be used for cladding supports. For example, very often durable and aesthetically attractive granite is used for this purpose. Such cladding can be hinged or conventional. In the first case, prefabricated plates are used for finishing. In the second, the stone itself is used directly. In the latter case, the material is embedded simply in the concrete of the support. Granite slabs are fastened with bandaging seams.
Also, bridge supports are classified into frame, hollow and massive. The latter are distinguished by the fact that they do not have any voids in their internal cavity. It is these supports that are used in the construction of bridges that experience very heavy loads.
Massive concrete supports are divided into groups according to the type of material used in the construction. In this regard, the following constructions are distinguished:
- stone;
- concrete;
- butoconcrete.
Classification by location
In bridges thrown across the river, supports are also divided into:
- intermediate;
- floodplain;
- riverbed.
Intermediate supports are located, as can be judged by their name, between the abutments. Channel elements support spans in the low water zone. That is, in the central part of the bridge. Floodplain supports are installed outside the middle low water. That is, around the edges. In railway and road bridges, the corresponding elements are called end (butts) and intermediate.
Bridge foundationscan be prefabricated, monolithic or piled. Also sometimes used and special designs on the fall wells. In any case, the foundation of the support must necessarily ensure its maximum stability.
Views by design and material used
On this basis, all bridge supports are classified into:
- rack;
- pile;
- columnar.
In the first type of supports, the part located above the edge of the foundation is made of racks. The second type of structure consists of two rows (in some cases one) of piles, united on top with a nozzle. It is this variety that is most often used in the construction of bridges today. Pile supports, in turn, are prismatic or tubular.
The third type of supports are elements made of hollow or massive pillars. In some cases, such structures can be combined with a nozzle, in others they cannot. The lower part of the pillars of such supports is located in the ground and acts as a foundation.
Basic elements
Supports are quite complex structures, during the construction of which, as already mentioned, certain rules must be observed. At the design stage of bridges, the most reliable type in this particular case is selected. This takes into account, of course, the economic feasibility of erecting supports of just such a design.
The main part of any support is called the body. Also in the design of these elements of the bridge, independing on their variety, may include:
- spacers - reinforced concrete parts that unite the tiers;
- openers - cantilever side walls of abutments that do not have a foundation and are designed to hold soil in the embankment of the passage;
- under-truss slabs;
- cabinet walls - elements of end supports that protect the end of the span from the soil of the embankment in the passage;
- crossbars in massive supports - upper reinforced concrete elements with consoles.
Particularities of bridge design
When drawing up the drawings of such structures, a variety of factors must be taken into account. Projects of river and sea bridges are developed in such a way as to preserve, among other things, the natural water regime at the crossing. This ensures their maximum reliability.
Actually, when developing a construction plan, depending on the type of bridge for its intended purpose, take into account:
- depth of groundwater;
- structure of soil in normal and frozen state;
- climatic features of the area;
- vegetation features of the area;
- probability of flooding;possibility of channel deformation, etc.
What other important factors to consider
In addition to hydrological and weather loads, when designing a bridge structure, possible wind and seismic loads are also taken into account without fail. The most difficult stage in drawing up drawings of such structuresis the calculation of internal forces under the most unfavorable combinations of external influences. This ensures maximum reliability of bridges during subsequent operation.
Design
When choosing a specific type of supports, factors such as:
- labor intensity of installation works and their timing;
- material consumption;
- construction cost.
The most inexpensive and at the same time reliable type of supports are considered to be pile. Rack-mounted are usually used at medium and low heights. During the construction of river bridges, structures with a massive base part and a hollow or frame surface part are most often erected. The grillage plates of the pillars at the bridges are placed above the ground surface.
Supports are designed in accordance with the requirements of such regulatory documents as:
- SNiP 2.05.03-84;
- SNiP 2.02.01-83;
- SNiP II-18-76;
- SNiP II-17-77 and some others.
Features of bridge construction
When building similar structures, first of all, the requirements set forth in STO NOSTROY 2.6.54 and SP 46.13330 are taken into account. When drawing up a bridge drawing, it is important not only to carefully work out its structure, but also to pay attention to the choice of materials. For example, concrete in the construction of such structures can only be used the highest, waterproof (for river bridges) grades. The same applies to fittings, consumables and other accessories.
Work order
During the construction of bridges, a variety ofEvents. But this procedure necessarily includes the following steps:
- preparatory activities;
- formwork erection;
- reinforcement;
- pouring concrete;
- concrete care;
- closing events.
During the construction of bridges, adjustable or sliding formwork can be used. In any case, such a form is made of metal parts lined with baked plywood. When pouring massive supports and combined elements, the reinforcing cage is increased in the course of work.
Moving formwork is filled with concrete over the entire area of the pylon or rack in several layers. In a sliding form, the mortar is laid at a speed of at least 7 cm / h to a height of 110 cm. The first rise of the formwork is carried out 2.5-3 hours after the start of concreting. Consolidate the solution during the pouring process using internal vibrators with a flexible shaft.
The biggest bridges in Russia
Bridges are an important part of the economic infrastructure of any country. A huge number of such structures have been built on the territory of Russia. At the same time, the largest bridges at the moment in our camp are:
- President across the Volga - 5825 m;
- Amur - 5331 m;
- Yuribey - 3893 m.
Modern grand rack
Of course, life does not stand still, so the construction of bridges continues in our country today. For example, one of these construction projects, attractingattention of the public is the Kerch bridge. After the construction is completed, it will become the largest in Russia. The scale of this modern construction is indeed grandiose. The length of the new bridge will be three times longer than that of the Presidential bridge on the Volga. This indicator at the end of construction will be as much as 19 km.
How the work is progressing
Surprisingly, the first draft of the bridge across the Kerch Strait was developed even before the revolution - by decree of Nicholas II. They did not build such a structure then due to the fact that the First World War began. They returned to the idea of building such a structure in the time of Stalin. In 1944, a railway bridge was even built across the Kerch Strait. However, it soon had to be dismantled due to ice damage to part of the supports.
Another sketch of the Kerch bridge was drawn up in 1949. In 2010-2013. Ukraine and Russia also discussed the creation of a transport line across the strait. In this regard, even a bilateral agreement was concluded. However, construction of the bridge began only after the annexation of Crimea to Russia.
Today (summer 2017) this grandiose building is already at the final stage of construction. This fall, the bridge from the mainland to the peninsula, according to officials, can even be walked on foot. In the fall, it is planned to install the main span in the Kerch-Yenikalsky Canal. From August 1, it is planned to install arches on the bridge supports. Each of these elements consists of 200 large parts. Arches are installed on massive fairway supports. Their height is as much as 35 m above the levelwater.
The project of a bridge across the Kerch Strait is actually unusual. Its implementation is, of course, a very responsible matter. This building of the century is being erected by the Stroygazmontazh company. The construction of a bridge across the strait will cost about 230 billion rubles. Its length will be, as already mentioned, 19 km. The bridge will have 4 lanes in total. The width of each will be 3.75 m. At the same time, another 4.5 m is allocated to the shoulders.
Supports for the construction of the Kerch bridge are reinforced concrete tubular and prismatic piles. To protect them, the project provides for a grillage. Due to the presence of this element, the bridge will later be able to easily withstand, for example, an earthquake of up to 9 points.
