The main advantage of steel roof frames, in comparison with cobblestone, is its strength and durability. Metal, of course, can withstand much greater loads than wood. The main disadvantage of such farms is primarily their high cost and some difficulty in installation.
In private housing construction, structures of this type are used extremely rarely. Basically, they are mounted during the construction of various kinds of industrial, warehouse and utility buildings of a large area. In private households, such farms from the corner are usually welded only when assembling some small metal architectural structures, for example, arbors or canopies.
What are
The main structural elements of the metal truss are:
The elements of such rafter systems can be fastened by welding, bolts or rivets. There are farm units from corners and pipes with a direct adjacency and on fittings.
The upper and lower zones of such metal supporting structures can be assembled, for example, from a profiled pipe. When installing the roof frame of large industrial buildings for this purpose, in some cases, more durable channels are also used.
Corners for the erection of supporting structures of roofs are also used quite often. Sometimes farms are assembled from single metal products of this type. But in most cases, the belts are mounted from corners connected by the brand. This allows you to assemble much more durable structures.
For welding the upper belt of such systems, it is supposed to use angles with different widths of shelves. For the lower screed of the truss, material equilateral in the front plane is taken from the paired corners. This technology allows you to assemble the most durable and durable structures. In the upper zone, in this case, the corners are connected on the smaller side.
The nodes of farms from paired corners are designed on cuts. The lattice rods are attached to the latter by flank seams. The cuttings themselves lead around the corners. In this case, the node is the most reliable.
Elements of the lattice of farms from the corner are:
This part of the construction of the metal rafter system is assembled both during the construction of large buildings and small architectural forms, in most cases from a single corner. Sometimes a profiled pipe of a small cross section is also used for this purpose.
Additional elements of trusses from the corner are usually bearing Z-profiles, on which the roofing material itself is subsequently fastened. Sometimes such elements are not mounted when assembling the supporting structure of the roof.
In the construction of small architectural forms, among other things, simple trusses without belts can be used, which are structures that form one plane. In the manufacture of such systems, a triangular frame is first welded. Further, it is strengthened by stiffeners and struts.
The most common types of farms by design
Most often, metal rafter systems are used as the frame of the roof of buildings and small architectural forms:
During the construction of buildings , arbors and canopies, in most cases, the first type of trusses from a corner and a pipe is mounted. Such structures can be welded for both single-pitched and double-pitched roofs.
Arched trusses are more difficult to install and more expensive. For their assembly in the private sector, among other things, you will have to purchase equipment such as a pipe bender. The main advantage of such farms, in comparison with triangular, is aesthetic appeal. In private households, such structures are mounted most often when assembling canopies and peaks of attractive architecture and design, forged and carved with a coating of polycarbonate, flexible tiles, shingles.
What other types can be mounted
When erecting small architectural forms and small buildings, it is usually arched or triangular farms from a single corner that are usually collected. When erecting buildings of a large area, structures of this type can also be mounted:
with a parallel belt (rectangular) - the most economical option, mounted from identical elements;
polygonal - an analogue of a broken gable roof;
trapezoidal;
Segmented - similar in shape to arched, but at the same time having a more complex structure.
Shed trusses from the corners always have a triangular shape.
Types of Gratings
Part of truss structures located between the upper and lower zones, in turn, can be:
triangular - struts are interconnected without racks;
triangular with additional racks - vertical elements are mounted near each strut;
cross - in the front plane resembles a row of rectangles with diagonals-struts;
with ascending or descending braces;
strangel complex shape;
cross, in the front plane representing a series of rhombuses, assembled without the use of racks;
rhombic, similar to a cross, but mounted with racks;
half-diagonal ("herringbone" lying on its side).
How to make a project
Before starting an independent assembly of the farm from paired corners, single or pipes, you should determine:
The number of slopes of the farm made of metal can be different. Using such structures, it is allowed to erect multi-gable complex roofs. However, in private households, most often, when building small architectural forms, they still mount single- or gable farms. Such designs are easy to assemble and yet reliable.
The angle of inclination of the slopes of the roof with a metal truss is determined depending on the wind and snow load and some other factors. It is difficult to independently calculate this parameter for steel rafter systems in accordance with all the rules, unlike wooden ones, without special knowledge. Therefore, in most cases, the owners of suburban areas simply find the typical farm formula of one design or another. Next, the necessary indicators are substituted into it.
Formula Examples
In order to perform truss calculation from paired or single corners, it is first necessary to determine the height and length of the structure. The last indicator in this case will correspond to the distance that the structure will close during operation (building width plus overhangs).
The optimal height of the farm can be determined by the following formulas:
Here H is the height of the truss, L is its length. Braces in the lattice of metal frames of roofs can be installed at an angle from 35 ° to 50 °. In this case, the optimum value is considered to be 45 °. When using struts mounted in this way, the supporting structure is the most durable.
Calculation of the farm from the corners of the arched
In such designs, the required length of metal products for the lower zone is determined using the following formula:
mh = pi × R × a × 180, where mh is the length of the corner, pi = 3.14, the R-radius of the circle, and the angle between the radii of the circle drawn to the extreme points of the lower zone.
If the span in small architectural form is less than 6 meters, instead of a complex truss, it is allowed to use just a single or double beam, bent under the selected radius. In this case, to assemble the supporting structure of the roof, it is usually not a corner that is used, but a profile pipe.
At the end of the calculations, when drawing up the roof project, it is supposed to make a drawing indicating the dimensions of all the elements, their angles, etc. According to this scheme, the truss is then assembled from paired corners or simpler structures.
Installation Rules
When assembling metal roof trusses with your own hands, it is recommended to be guided by the following rules:
Supporting vertical pillars of large metal structures (canopies, buildings) are best made not from a single corner, but from a profile pipe. Such metal rolling is more durable. It is desirable to make racks of the farms themselves from the same material. From the corners in such designs, you can make a frame and braces.
It is necessary to fasten the structural elements of the farm using tacks and twin corners.
In the upper zone, the parts should be joined using I-beam angles.
In the lower zone, equilateral corners are used in the mates.
For joining the main parts of the farm, having a large length, you should use overhead thick steel plates.
In order to exclude the possibility of deflection of the belts, the roof on a metal truss is mounted so that its weight falls on the nodes of the truss from the corners.
Assembly order
The first step in the self-installation of metal rafter systems, of course, is the cutting of the corner and other metal products, according to the drawing. Further:
assemble the farm structure on the ground;
carefully check its geometry using a square and level;
weld the assembled frame using patch plates and corners where necessary.
The procedure for assembling a farm on the ground is usually as follows:
lay longitudinal pipes or corners (with a twin farm, first weld the brands);
weld racks;
welded braces and jumpers.
At the final stage of farm assembly, the quality of the welded joints is checked, including. The design, of course, should be as reliable as possible.
After the first farm is ready, proceed to the assembly of the next. Thus, all the supporting elements of the rafter system of the structure are welded.
Frame assembly
The farms prepared in this way are lifted to the racks or box of the building at the next stage. Pre-assembled from the corner or pipe the upper strapping of the structure and support beams. The farms are welded, and then connect them to each other with a ridge element and intermediate jumpers. The latter are usually mounted at a distance of at least 1.5 m from each other.
At the final stage, all truss structures from a metal corner or pipe are ground, primed and painted. After this, the roof cladding is actually started.
Angle Requirements
All metal trusses used for roof construction are conditionally divided into three categories:
It is believed that roofs of the first type should be mounted using trapezoidal trusses with a height of 1/7 to 1/9 of the span. If the ceiling is not supposed to be subsequently hemmed in the structure, the braces in such a structure are installed in the form of a triangular lattice.
To assemble roofs with a slope angle of 15 to 22 °, trusses with a height of 1/7 of the span are usually used. This allows you to mount the most reliable design. If you need a large height (0.16-0.23 parts of the span), the lower belt is broken. When using this method, the mass of the frame can be reduced by 30%.
To install trusses from steel corners with a broken lower belt is allowed only on structures with a span of not more than 20 m. Otherwise, it is supposed to mount Polonso structures.
For farms with a slope angle of 22-30 °, a height of 1/5 of the span is usually chosen. In this case, the structure will turn out to be optimally light and subsequently it will quickly drain rain and snow. Mounted on such buildings are usually triangular trusses from the corners.
Roofs with such an angle of inclination of the slopes are covered in most cases with slate or metal sheets. For long flights from 14 m, farms with descending braces are most often used. Such structures well tolerate significant snow and wind loads.
Twin farms
Such systems are often mounted on racks and boxes when the span exceeds 10-12 m. The whole truss in this case will weigh a lot. And this in turn will cause difficulties with its transportation and installation on the box. Therefore, for wide spans, the system is first divided into two fragments, and then connected at the top by puffs and welding.
When designing and calculating paired farms, one should, among other things, take into account the fact that both of their parts must be absolutely identical. That is, half should not be divided into left and right. Otherwise, confusion may arise when mounting trusses on a building box.
When assembling such double structures at the top, it is desirable to use, in addition to welding, as many bolt joints as possible. In this case, the nodes will be the most durable.
What are the Polonso Farms
Such designs consist of two triangular parts connected by a screed. The main advantage of such farms is the lack of need for using long braces. Due to this, the design is not only durable, but also light.
Such farms are mounted, as already mentioned, on long spans. Most often they are used in the construction of large industrial buildings.
Wood farms
In order to save money, in the construction of buildings and small architectural forms, combined support structures can be used, among other things. For example, the bottom screed, trusses and puffs are often made of pipe and angle, and the upper belt is made of boards or beams.
Lumber for such structures is chosen well-dried and with a minimum number of knots. The moisture content of the timber or boards should be no more than 12%. Before using for assembly of combined supporting structures, it is advisable to dry the lumber for an additional several months. Otherwise, due to shrinkage, the wood in the finished frame can later crack (the metal will retain its size).
In order to make such farms more durable, they are usually reinforced. In most cases, a steel bar is used for this purpose. Also, wood-metal trusses can be reinforced with fiberglass reinforcement. Rods with wood are usually bonded using epoxy glue. At the same time, the reinforcement is passed inside the upper zone (in glued structures).