XII Международная студенческая научная конференция Студенческий научный форум - 2020

Since ancient times on the way to the urban planning and the development of civilization there have been all sorts of obstacles, whether rocks, ravines, rivers, seas and gorges. They had to be overcome, and for doing this people came up with one of the greatest buildings – the bridge.

A bridge is an artificial structure that is a link between two points. It follows that combining two banks the bridge forms a continuous path of communications, giving impetus to progress in the development of the states and their interaction, establishing of trade relations, facilitating of transportation, development of industry, agriculture and their support. And for each of these ways of communication there is a definition – an artificial structure built across a river, lake, swamp, strait or any other water obstacle, called a bridge. Overpass is called an engineering structure built across the road and a structure across a ravine or gorge-a viaduct.

One of the first bridges was an aqueduct (part of the conduit in the form of a bridge over a ravine, river or road, on which the city was supplied with clean water). The first aqueducts were built in the IV century BC, later began the construction of viaducts (bridges, designed for the organization of roads), they were characterized not only by functional qualities, but also by aesthetic.

The bridge is a quick way to cross a water obstacle, so it should not only be durable, have sufficient load capacity, be safe while moving, but also when it is built the features of the terrain and the purpose of the structure should be taken into account. There are certain types of bridges. They are divided into:

1) Beam. This bridge is considered to be one of the simplest structures, because the spans as well as the overlaps between the supports are beams. The main beams of such a bridge are of two types: continuous and through section, and the supports perceive only vertical loads from the span elements, i.e. they work on bending.

Figure 1. – Girder bridge (or beam)

2) Truss. This scheme is used for the bridge length from 40 to 150 meters. Steel rolling is used for construction. We can also say that the truss structures are similar in scheme to the beam, however in the span structures trusses are put.

Figure 2. – Bridge truss

3) Floating and pontoon bridges. These structures have such a distinctive feature as floating spans or pontoons (supports). Such schemes can be considered temporary, because they do not provide a rigid frame and rigid attachment to the shore.

Figure 3. – Floating and pontoon bridges

4) Humpback. This type of construction has a curved upward shape, which gives it an advantage, because it does not deform and works only on compression.

Figure 4. – Humpback bridge

5) Push-in type. This type of bridge differs from a girder bridge in that the horizontal and vertical components of the load – the strut – act on the supports.

Figure 5. –Push-in type bridge

The bridges can also be divided into five categories:

1) Frame-in. The design uses frames, racks serve as supports, and spans serve as crossbars.

2) Hanging or suspended-in. In this case flexible elements (ropes, cables, chains) are used for the supporting of structure. For additional rigidity trusses and beams are used.

3) Cable. The supporting structure in this case is a cable-stayed truss made of steel ropes.

4) Arch. The design of this bridge converts horizontal loads into vertical, the bridge itself works on compression.

5) Combined. This scheme combines beam and arch schemes.

Construction of bridges involves many points, which include development sites, build structures, towers, spans, elimination of building sites, testing, etc. Design of bridges is performed depending on the size of structures in one or two stages. Large bridges are designed in two stages, small bridges and bridge repair – in one.

The construction of the foundation of the bridge is a very time-consuming process, which considers the methods of soil development, fastening and drainage of pits and underwater concreting for the device of pits. Pile foundations, in case of a washout or its absence by their pressure water, arrange by means of shock and vibration method of immersion. Drilling of wells and their concreting is used at the device of drilling piles. For reinforced concrete shells or metal pipes during immersion, vibro-loaders are used, while developing the soil in the inner cavity. The plate of the grillage is constructed in several possible ways of its device in the fence, with the help of various jumpers, a bottomless or floating box. It is also necessary to choose the most rational auxiliary device for the production of works, taking into account the construction of the foundation and construction conditions.

The structure of the superfundament part includes formwork, reinforcement and concreting, concrete care, as well as decking and surface finishing. First of all, the formwork device is performed, it is made of such materials as: softwood wood, bakelized plywood and steel formwork. Also, in order that the formwork does not leave traces, stains or corrosion, special lubricants and anti-adhesive coatings are used.

The next stage is reinforcement and concreting, which in turn is carried out with the help of a crane (floating, boom, portal and tower), it is installed on the scaffolding near the concreted object. Recently, using a concrete pump, where the mixture is loaded into a hopper and fed into the formwork to a height of 90 m. If the bearing prefabricated or precast-monolithic, the building advancements part consists of the installation of concrete or concrete blocks, concreting joints, filling with a mixture of the internal cavity, the mounted beam support and concrete pottermania. For superstructures installation technology was developed, taking into account the production of works with the use of modern machines and equipment.

Prefabricated beam spans can be divided into two types: ribbed and slab. The forming element is the individual mounting blocks (beams, plates). Also, spans are divided by type of reinforcement into structures with frames of reinforcement without prestressing and with tensioned reinforcement mainly from bundles of ropes K-1400. Less often when installing use slab superstructures of vaulted, hollow and u-shaped plates; during operation, their connections are upset, so on top of such buildings laid monolithic reinforced concrete overlay plate. More often we use precast monolithic superstructures with precast ribs, and after their installation, the monolithic slab is concreted in place. When installing superstructures, great attention is paid to the installation of beams on the supporting parts, deviations should not exceed 5-10 mm from the design position. Also, for safety reasons, after installing the beams, it is necessary to provide a reliable fastening of the mounted units in the design position. To do this, we install the temporary mounting stand, and then do the grouting blocks, then all the temporal relationships are dismantled. For monolith t-beams, first of all we let out armature from a plate, after we establish longitudinal anti-shrink fittings armature, suspend a panel timbering and at the end concreted joint, carry out care of concrete.

Thus, we can say that at each stage, quality control is carried out with the participation of representatives of the customer, while the acts of acceptance of works are drawn up, which assess the quality of work performed and conclusions about further work.