The most common meaning of the word "farm" is an agricultural enterprise intended for animal husbandry. But now it’s not about the place of conducting the subsidiary farm. All information about probably the oldest building construction, which is still relevant in modern life, is collected here. It is widely used in construction, especially in the construction of bridges and sports facilities.
A truss is a system consisting of rods that remains geometrically unchanged when its rigid nodes are replaced by articulated ones. Truss beams, which are represented by a combination of two or three-span uncut beams and a tie rod, also belong to it.
Where is it used?
As already mentioned, a farm in construction is an indispensable element. With its help, builders facilitate the construction of the structure and reduce the consumption of necessary materials. The construction of bridges, stadiums, hangars, as well as decorative structures such as pavilions, stages, podiums, etc. is not without the use of a farm.
When designing the hull of a ship, aircraft, diesel locomotive, strength calculation takes place in the same way as the calculation of the load on the farm.
Classification
A farm is a structure consisting of rods that are interconnected in nodes and form a statically unchanged system. Farms can be classified according to many properties.
By design capacity
- Lungs . They use a single-stage section. Light farms are most often used in industrial construction.
- Heavy . Heavy farms are used in the construction of tower cranes, sports stadiums, etc. They use rods of a more complex cross section than in the lungs. As a rule, they consist of two to three parts due to the large design length and the load imposed on them. Most often, a two-stage section with a two-plane nodal conjugation is used.
By common features
- By appointment. According to the purpose of the farm, there are tower, bridge, crane, truss coatings, supporting structures, etc.
- By type of material. Wood, steel, aluminum, reinforced concrete, etc. - From all this a construction farm can be made. This is an essential advantage of this system. You can also combine several types of material.
- By design features. There are various types of sections, types of gratings, types of supporting structures, as well as types of belts for the building structure of the truss.
Spatial feature
- Flat . Farms take on a vertical load, because x rods are located in one plane.
- Spatial . Distribute the load over its entire area. The spatial farm is formed of many flat farms, interconnected by special methods.
Type
- Virendel beam.
- Farm Warren.
- Farm Pratt.
- Farm Bolman.
- Finca Farm.
- Triangular farm.
- Kingpost
- Cross strut farm.
- Lattice urban construction.
- Farm under the overhead light.
Design features
The classification of the farm by design features is quite extensive. Further, each of the features will be considered in more detail.
Section Types
The cross section in the construction farm is made of rolling profiles. It can be in the form of:
- Corner (single or double).
- Pipes (round or square).
- Channel.
- Taurus or I-beam.
Belt types
The outline of the belt can be represented as:
- Trapezoid . Its advantage is that this type of belt tightens the frame unit, respectively, with it the rigidity of the building increases.
- The triangle . This type of belt is used for beam and cantilever systems. It has a lot of disadvantages, such as irrational metal consumption during load distribution, the complexity of the support node, etc.
- Parabolas . This belt is the most laborious. Therefore, segmented farms are used very rarely.
- Polygon . Polygonal farms are used more often than segmented ones. Because they fracture in the nodes of the design is not so noticeable.
- Parallel belts. Most often used to cover industrial buildings. They have an identical knot pattern, lattice elements of equal size, and they also have repeatability of elements and parts.
Grid Types
There are six typical grill options:
- Triangular.
- Rhombic
- Shprengelnaya.
- Cross.
- Squinting
- Half-crooked.
Types of support
There are 5 types of supporting structures. In order to select the reference node, you need to know the calculation scheme. It depends on it whether the support assembly is articulated or rigid. Types of supports:
- Beam or cantilever.
- Arched.
- Cable-stayed.
- Frame.
- Combined.
Operating principle
The uniqueness of this design lies in its "immutability" under the influence of external factors. The load on this system is quite large. A farm is a multitude of triangles combined into one design. The load in them is concentrated at the junction of nodes, because the rods better show their properties in the process of compression-tension, and not on kink. In modern construction, rigid, rather than articulated, rods are most often used. From this it follows that when one of them is separated from the whole structure, they will remain unchanged with respect to each other.
Principle of truss calculation by cutting corners
This method of farm calculation is the simplest. This method is taught in many technical educational institutions.
A farm is a structure whose load is concentrated in its nodes. Therefore, it is necessary to calculate all external factors that will be the load on the nodes. Then - calculate the reaction of the support and find the node in which there are 2 rods with the force applied to them. It is conditionally necessary to separate the rest of the farm and get a node in which there will be several known values and 2 unknowns. Then you need to make equality on two axes and calculate the unknown values. The next node is allocated in the same way, and so on, until the farm is calculated.
The main types of farms
- The Virendel beam is a system where all its parts form rectangular openings and thereby join into a rigid frame. In its design, it does not fit the strict term "farms", because there is no pair of forces in this beam. It was developed by the Belgian engineer Arthur Virendel. But since this design is quite massive, it is rarely seen in modern architecture.
- Farm Warren. This is a simplified version of the Pratt-Hove design. It works on the principle of compression-tension. Most often made of rolled steel.
- Farm Pratt. The patent for this facility belongs to his father and son from Boston. Caleb Pratt and Thomas Wilson were two engineers. They used the squeezed parts vertically and the stretched ones horizontally. Therefore, the load is equally well distributed both from above and from below.
- The Bolman farm has a rather complicated and inconvenient design. This building got its popularity in the USA because of the political merits of its creator. The inventor spoke eloquently about the farm, even if not everything was true. Bolman managed to advance his invention with the help of the American government, which sometimes forced city planners to use this design when designing bridges. Among the owners of building farm patents there are many of our compatriots, but not a single “Russian” farm has yet advanced to the masses in such an original way.
- Fink Farm is a simplified version of Bolman Farm. He simply shortened all its elements and thereby made it more effective. It also has similarities with the design of the Pratt farm. It differs from it only in the absence of a lower beam.
- Triangular farm. It is also called "Belgian." This is a modern design, which is presented in the form of triangles with trusses.
- Kingpost is the easiest farm option. It is a pair of supports resting on a vertical beam.
- The trellised city structure was created to replace huge wooden bridges. It is quite simple in design. For her, ordinary wooden boards are used, connected to each other at an angle, which, in turn, form a lattice.