Supports are called the supporting 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.
The main types of manufacturing method
Supports are being assembled using technologies that subsequently ensure maximum reliability of the bridge and its ability to withstand the necessary loads. By the method of construction, they can be:
- monolithic;
- national teams;
- prefabricated monolithic.
Installation of monolithic bridge supports is carried out right on the spot by pouring concrete into the formwork. Prefabricated are installed from pre-harvested concrete or reinforced concrete elements. At the same time, the latter are connected with the exact observance of certain standards. Precast monolithic supports are structures of a combined type. That is, some of them are poured in place, and some are collected.
Monolithic supports, in turn, can belong to the group of structures:
- with facing;
- without facing.
Different materials can be used for facing the supports. For example, very often for this purpose durable and aesthetically attractive granite is used. Such cladding may be hinged or conventional. In the first case, pre-made boards are used for decoration. In the second, the stone itself is used directly. In the latter case, the material is simply embedded in concrete piers. Granite slabs are fastened with dressing of 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 inner cavity. It is these supports that are used in the construction of bridges experiencing very strong loads.
Massive concrete supports are divided into groups according to the type of material used in the construction. In this regard, the following structures are distinguished:
- stone;
- concrete;
- concrete concrete.
Location classification
In bridges thrown across the river, supports are also divided into:
- intermediate;
- floodplain;
- channel.
The intermediate supports are located, as can already 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 set outside the middle low water. That is around the edges. In railway and automobile bridges, the corresponding elements are called end (abutments) and intermediate.
The foundations of bridge supports can be prefabricated, monolithic or pile. Also, special designs at lowering wells are sometimes used. In any case, the foundation of the support must necessarily ensure its maximum stability.
Types of construction and material used
On this basis, all bridge supports are classified into:
- rack-mount;
- pile;
- columnar.
In the first variety of supports, the part located above the foundation edge is made of racks. The second type of structure consists of two rows (in some cases one) of piles, combined on top of the nozzle. It is this variety that is used in the construction of bridges today most often. 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 constructions can be combined with a nozzle, but not in others. The lower part of the pillars of such supports is located in the ground and actually plays the role of the foundation.
Essential elements
Supports are quite complex structures, 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 the construction of supports of just such a design.
The main part of any support is called the body. Also, the design of these elements of the bridge, depending on their variety, may include:
- gaskets - uniting reinforced concrete parts;
- openers - cantilever side walls of foundations that have no foundation and are designed to hold the soil in the embankment of the passage;
- sub-truss plates;
- cabinet walls - end support elements protecting the end of the span from the soil of the embankment in the passage;
- crossbars in massive supports - upper reinforced concrete elements with consoles.
Features of bridge design
In drawing up 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 transition. This ensures their maximum reliability.
Actually, when developing a construction plan, depending on the type of bridge for the purpose, take into account:
- groundwater depth;
- soil structure in normal and frozen state;
- climatic features of the area;
- features of the vegetation cover of the area;
- the possibility of high water; the possibility of deformation of the channel, etc.
What other important factors must be taken into account
In addition to hydrological and weather loads, when designing the construction of bridges, possible wind and seismic are also taken into account. The most difficult step in drawing up drawings of such structures is the calculation of internal forces at the most unfavorable combinations of external influences. This ensures maximum reliability of bridges during subsequent operation.
Design
When choosing a specific type of support, factors such as:
- the complexity of installation work and their timing;
- material consumption;
- construction cost.
The most inexpensive and at the same time reliable type of supports are pile. Racks are usually used at medium and low altitudes. During the construction of river bridges, structures with a massive base part and a hollow or frame surface are most often constructed. Plates grillage racks at the bridges are located above the ground surface.
The 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 the construction of bridges
During the construction of such structures, the requirements set forth in STO NOSTROY 2.6.54 and SP 46.13330 are taken into account primarily. When drawing up a drawing of the bridge, it is important not only to carefully study 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 with the highest, waterproof (for river bridges) grades. The same applies to fittings, consumables and other components.
Work order
During the construction of bridges, a variety of activities can be carried out. But this procedure without fail includes the following steps:
- preparatory activities;
- construction of formwork;
- reinforcement;
- concrete pouring;
- concrete care ;
- final events.
During the construction of bridges, removable or sliding formwork may be used. In any case, this form is made of metal parts lined with bakelized plywood. When pouring massive supports and combined elements, the reinforcing cage is increased during the course of the work.
Replaceable formwork is filled with concrete mixture over the entire area of the pylon or rack in several layers. The mortar is placed in a sliding form at a speed of at least 7 cm / h to a height of 110 cm. The first formwork rise is then carried out 2.5-3 hours after the start of concreting. Seal the solution during the casting process using deep vibrators with a flexible shaft.
The largest 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 in our camp at the moment are:
- Presidential via the Volga - 5825 m;
- Amursky - 5331 m;
- Yuribey - 3893 m.
Modern grand stand
Of course, life does not stand still, so the construction of bridges continues in our country today. For example, one of these construction projects that attract close attention 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 really grandiose. The length of the new bridge will be three times longer than that of the President on the Volga. This indicator at the end of construction will be as much as 19 km.
How do the work progress
It is not surprising, but the first draft of the bridge across the Kerch Strait was developed before the revolution - by decree of Nicholas II. Such a structure was not built then because the First World War began. They returned to the idea of building such a structure during the time of Stalin. In 1944, a railway bridge was even built across the Kerch Strait. However, he soon had to be dismantled due to ice damage to some of the supports.
Another sketch of the Kerch bridge was made in 1949. In 2010-2013. Ukraine and Russia also discussed the creation of a transport branch across the strait. In this regard, even a bilateral agreement was concluded. However, the construction of the bridge began only after the annexation of Crimea to Russia.
Today (in the summer of 2017) this grandiose building is already at the final stage of construction. This fall, according to officials, it will even be possible to walk on the bridge from the mainland to the peninsula. In autumn, 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 mounted on massive fairway supports. Their height is as much as 35 m above water level.
The design of the bridge across the Kerch Strait is actually unusual. Realization of it is, of course, a very responsible matter. The Stroygazmontazh company is building this construction of the century. The construction of a bridge across the strait will cost about 230 billion rubles. Its length will be, as already mentioned, 19 km. In total, there will be 4 lanes on the bridge. Each will be 3.75 m wide. At the same time, 4.5 m more are allotted to the curbs.
Supports for the construction of the Kerch Bridge use pile reinforced concrete tubular and prismatic. To protect them, the project provides a grillage. Due to the presence of this element, the bridge can subsequently easily withstand, for example, an earthquake of up to 9 points.