Bridges are structures that help to overcome obstacles, reduce travel time. Modern structures are built from materials that can withstand heavy loads.
What are the bridges
A bridge is a continuation of the road through an obstacle. It can connect the banks of a river or pass over a busy highway, forming an interchange. Modern bridges are classified according to the following criteria:
- for the main purpose;
- by constructive decision;
- in length and width;
- by the term of operation;
- by the type of building materials used.
Many modern bridges have a specific purpose. On this basis, they are classified into:
- pedestrian;
- road;
- railway;
- combined.
Combined bridges imply the movement of automobile and rail transport (trams, trains) along them. Such designs are universal, but to ensure the safety of people, precise traffic control is sometimes necessary.
According to the dimensional characteristics, bridges are distinguished:
- small (length up to 25 m);
- medium (length 25-100 m);
- large (length over 100m);
- extracurricular.
Out-of-class facilities include structures whose length exceeds 300 m, and the distance between spans is 60 meters or more. This type of structure also includes complex bridges with non-standard static schemes, as well as those whose length exceeds 500 m, and the distance between spans is less than 60 m.
Modern bridges are built from different materials, each of which has its own advantages and disadvantages. On this basis, structures are divided into:
- wooden;
- stone;
- reinforced concrete;
- steel;
- steel-reinforced concrete.
To determine what type of bridge the bridge belongs to, you need to know what material the base of the superstructure is made of. If the supports and spans are laid out, for example, from masonry, but there are wooden elements in the structure, the structure will still be considered stone.
For steel-reinforced concrete bridges, the base is made of reinforced concrete and steel elements, joined together by anchors that absorb shear between steel and concrete.
According to the duration of their service life, bridges are divided into:
- temporary;
- permanent.
Permanent structures are constructed from more durable materials, since such structures require long-term use. Temporary structures are often made of wood.
Types of structures of modern bridges
Taking into account the constructive solution, bridges can be divided into several groups:
- beam;
- arched;
- console;
- cable-stayed;
- hanging (suspended).
Girder bridges
The girder bridge has a simple structure. It appeared very first, when people began to throw logs over water obstacles in order to be able to get to the other side. The girder bridge is a horizontal structure. It stands on supports on both sides. Its main elements are beams and trusses, which transfer the load to the supports of the bridge base. Beams and trusses form part of the structure, which is called a span. Spans are:
- split;
- console;
- uncut.
Modern beam bridges are built of reinforced concrete, steel, but there are also wooden structures, which are also reliable.
Arched bridges
The basis of the construction of an arched bridge is an arch (vault), which can be made of steel, reinforced concrete, individual reinforced concrete blocks. 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, the load is distributed to all intermediate and outer supports.
Suspension bridges
The main supporting structure of the suspension bridges is made of flexible elements, which include ropes and chains. It works in tension, and the roadway is suspended. Suspended bridges are called suspension bridges, but this term is not used in construction terminology.
This type of structure is used in cases where the length of the bridge is long, but it is not possible to install intermediate supports. Shipping canals are a prime example of such places. In the construction of modern suspension bridges, additional beams are used to reduce the load on the roadway. High-strength steel ropes are used as suspension supports. Suspension bridges have many advantages, including the ability to build high above the water and relative lightness. They can bend under the influence of strong winds or earthquakes without damaging the structure. Other types of bridges need to be built heavier and more massive. In some situations, lack of rigidity, on the contrary, is a disadvantage. Suspension bridges can bend when the load is unevenly distributed, which is why railway structures are rarely erected using this principle.
Cable-stayed bridges
Cable-stayed bridges are a type of suspension bridges. In this case, several pylons are connected to the roadway using steel cables (cables). In such bridges, the cables are connected directly to the pylons, and this is their difference from suspended structures. The main advantage of cable-stayed bridges is the lower mobility of the roadway. They can also be built for the purpose of moving rail transport.
Cantilever bridges
Cantilever bridges are structures with spans hanging outside the supports. They are used for large span lengths and widths. Currently, they are almost never built. Cantilever bridges look impressive, but they are difficult to manufacture and have other disadvantages. Their stability depends on the stability of the base span. If it is damaged, the entire structure can gradually collapse.
Frame bridges
In frame systems, the spans and the structure form a single structure. The frames significantly reduce the bending moment. Frame bridges do not have significant advantages over beam bridges, but at the same time, their construction requires large financial and labor costs. That is why they are rarely built. Their use is justified in the construction of bridges designed to cross deep gorges. In this case, inclined posts allow you to close long openings.
Some modern bridges are complex in structure and can be classified into several categories at once. When choosing the size of the bridge, its design features, manufacturing technology and material, the purpose must be taken into account. Not only the durability and strength of the structure, but also the safety of people depends on how deliberate and correct this decision turns out to be.
