A semi-trailer is a means of transport and a kind of trailers, designed for various loads transportation. It’s equipped with a base platform with a pivot axle in the front part. These elements are attached to a tractor unit’s truck bolster. Thus, a part of the gross weight is being transferred to the tractor unit’s axles. Such elements like lodgments are also installed. The front part in an unattached condition rests upon them. A semi-trailer can be broadlydivided into two parts – an undercarriage part and a load-carrying part.

The undercarriage part consists of a suspender, chassis and axles. Load-carrying capability, speed and stability depend on these elements. Contemporary semi-trailers are being equipped with air cushions. These cushions absorb road humps and ensure stability, what also means safety of a load. The gross payload of the entire semi-trailer depends on the axle loads. Chassis (or the frame) is also a very important structural element. Usually it is assembled with the help of screw-bolts to provide repair accessibility. The frame can also be solid, what increases stiffness and stability. Chassis is coated with an anti-wear and anticorrosive layer. Semi-trailer producers, as a rule, choose an undercarriage part components distributor by themselves.

Still, there are more modifications available for a load-carrying part. Depending on the purpose of use it can be made of steel, wood or plastic. As a rule, there are the following structural components present: a kind of floor or a frame,a basic frame, a layer of non-conducting material, retention equipment (for example, an anchor tire or rings), loading/unloading equipment and an internal frame for multistage load disposition. Tank wagons and special storage tanks for fuel and liquids transportation (such as ammonia) can be installed on the platform.

Materials, which are used to make a semi-trailer of, depend on the principal purpose of the vehicle, for example, there are special materials for semi-trailers that transport temperature-sensitive goods, heavy or bulky loads and machinery, etc. Thus, tilted or closed bodies and refrigerators are used to provide the safety of the load. A semi-trailer can also look like a tipper, designed for construction materials and loose cargos transportation. A low-loader for machinery and excavator transportation is concerned another modification.

In contrast to tractor units, semi-trailers are plain machinery produced by lots of companies, including manufacturing the vehicles that are ordered in advance. Krone, Schmitz, Van Hool and Kögel are the most well-known producers of standard semi-trailers.