The main advantage of steel roof frames, in comparison with paving stones, is strength and durability. Metal, of course, is able to withstand much greater loads than wood. The main disadvantage of such trusses is, first of all, 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 are usually welded from a corner only when assembling some small metal architectural structures, for example, gazebos or sheds.
What are
The main structural elements of a metal truss are:
- top belt;
- lower belt;
- grille located between them.
The elements of such truss systems can be fastened by welding, bolts or rivets. There are nodes of farms from corners and pipes with directadjoining and on gussets.
The upper and lower chords of such metal support structures can be assembled, for example, from a profiled pipe. When mounting the roof frame of large industrial buildings, in some cases, stronger channels are also used for this purpose.
Corners for the construction 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 the corners connected by the brand. This allows much stronger structures to be assembled.
For welding the upper belt of such systems, it is supposed to use corners with different widths of the shelves. For the lower screed of the farm, from paired corners, material is taken equilateral in the front plane. This technology allows you to assemble the most durable and durable structures. In the upper belt, in this case, the corners are connected along the smaller side.
Farm knots from paired corners are designed on gussets. Lattice rods are attached to the latter with flank seams. The gussets themselves lead to the corners. In this case, the node is the most reliable.
The elements of the truss lattice from the corner are:
- racks perpendicular to the axis;
- angled struts;
- sprengels or auxiliary struts.
This part of the construction of the metal truss system is assembled both during the construction of large buildings and small architectural forms, in most cases fromsolitary corner. Sometimes a profiled pipe of a small section is also used for this purpose.
Additional elements of corner trusses are usually load-bearing Z-profiles, on which the actual roofing material is subsequently attached. Sometimes such elements are not mounted when assembling the supporting structure of the roof.
When erecting small architectural forms, among other things, the simplest trusses without belts, which are structures that form one plane, can be used. In the manufacture of such systems, a triangular frame is first welded. Further, it is reinforced with stiffeners and struts.
The most common types of trusses by design
Most often, metal truss systems are used as the frame of the roof of buildings and small architectural forms:
- triangular;
- arched.
During the construction of buildings, gazebos and sheds, in most cases, the first type of trusses is mounted from a corner and a pipe. Such structures can be welded for both single-pitched and double-pitched roofs.
Arched trusses are more difficult to install and more expensive. To assemble them in a private household, among other things, you will have to purchase equipment such as a pipe bender. The main advantage of such trusses, in comparison with triangular trusses, is aesthetic appeal. In private households, such structures are most often mounted when assembling canopies and canopies of attractive architecture and design, forged and carved with polycarbonate coating, flexible tiles,shingles.
What other types can be mounted
When erecting small architectural forms and small buildings, arched or triangular trusses are usually assembled from a single corner. 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 - analogue of a broken gable roof;
- trapezoidal;
- segmental - similar in shape to arched ones, but having a more complex structure.
Single trusses from corners always have a triangular shape.
Types of gratings
Part of truss structures located between the upper and lower chords, in turn, can be:
- triangular - the struts are interconnected without racks;
- triangular with additional uprights - vertical elements are mounted near each brace;
- cross - in the front plane resembles a row of rectangles with diagonal struts;
- with ascending or descending braces;
- strengel complex shape;
- cross, in the front plane, which is a series of rhombuses, assembled without the use of racks;
- rhombic, cross-like but stud-mounted;
- half-diagonal (herringbone lying on its side).
How to make a project
Before you start self-assembly of a truss from twin corners, single or pipes, you should decide:
- with roof configuration;
- slope angle.
The number of metal truss slopes may vary. With the use of such structures, it is allowed to build, including multi-gable complex roofs. However, in private households, most often, when building small architectural forms, one- or two-slope trusses are still mounted. Such designs are easy to assemble and at the same time are reliable.
The angle of inclination of the roof slopes 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 truss systems according to all the rules, unlike wooden ones, without special knowledge. Therefore, in most cases, the owners of suburban areas simply find a typical farm formula of one design or another. Next, the necessary indicators are substituted into it.
Examples of formulas
To calculate a truss from double or single corners, you must first determine the height and length of the structure. In this case, the latter indicator will correspond to the distance that the structure will cover during operation (the width of the building plus overhangs).
Optimal truss height can be determined by the following formulas:
- for polygonal, parallel and trapezoidal - H=1/8L;
- for triangular - 1/4L or 1/5L.
Here H is the height of the truss, L is its length. Struts in the lattice of metal frames of roofs can be installed at an angle of 35° to 50°. In this case, a value of 45 ° is considered optimal. 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 belt is determined using the following formula:
mh=pi×R×a×180, where mh is the length of the corner, pi=3.14, R is the radius of the circle, a is the angle between the radii of the circle drawn to the extreme points of the lower belt.
If the span in a 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, not a corner, but a profile pipe is usually used to assemble the supporting structure of the roof.
At the end of the calculations, when drawing up a roof project, it is supposed to make a drawing indicating the dimensions of all elements, their angles of inclination, etc. According to this scheme, the truss is subsequently 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:
- Support vertical columns of large metal structures (canopies, buildings) are best made not from a single corner, butfrom a profile pipe. Such rolled metal is more durable. From the same material it is desirable to make the racks of the trusses themselves. From the corners in such designs, you can make a frame and braces.
- It is necessary to fasten the elements of the truss structure together using tacks and twin corners.
- In the upper chord, the parts should be joined using I-beams.
- Equilateral corners are used in mates in the lower chord.
- To join the main parts of the truss, which are long, overhead thick steel plates should be used.
In order to exclude the possibility of deflection of the belts, the roof on the metal truss is mounted so that its weight falls on the truss nodes from the corners.
Assembly order
The first step in the self-assembly of metal truss systems, of course, is to cut the corner and other metal products, according to the drawing. Next:
- assemble the truss structure on the ground;
- carefully check its geometry using a square and level;
- weld the assembled frame using overlay plates and corners where necessary.
The order in which a truss is assembled on the ground is usually as follows:
- lay longitudinal pipes or corners (with a pair of trusses, the Taurus is welded first);
- welded racks;
- weld braces and lintels.
At the final stage of the assembly of the truss, the quality of the welds made is also checked. The design, of course, should be as reliable as possible.
After the first farm is ready, start assembling the next one. Thus, all the supporting elements of the truss system of the structure are welded.
Assembling the frame
Trusses prepared in this way at the next stage are lifted onto racks or a building box. The upper trim of the structure and support beams are pre-mounted from a corner or pipe. Farms are welded, and then they are connected 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 angle or pipe are ground, primed and painted. After that, proceed to the actual roof sheathing.
Requirements depending on the angle of inclination
All metal trusses used for the construction of roofs are conventionally divided into three categories:
- with slope angle from 6 to 15°;
- 15 to 22°;
- 22 to 33°.
It is believed that the roofs of the first type should be mounted using trapezoidal trusses with a height of 1/7 to 1/9 of the span length. If the ceiling is not supposed to be hemmed in the future, the braces in such a structure are installed in the form of a triangular lattice.
For assembling roofs with slope angle from 15 to22° trusses are usually used with a height of 1/7 of the span length. This allows you to mount the most reliable design. If a greater height is needed (by 0.16-0.23 parts of the span length), the lower chord is made broken. Using this method, the carcass weight can be reduced by 30%.
It is allowed to install trusses from steel angles with a broken lower chord only on structures with a span of no more than 20 m. Otherwise, it is supposed to mount Polonso structures.
For trusses with a slope angle of 22-30°, a height of 1/5 of the span length is usually chosen. In this case, the structure will turn out to be optimally light and subsequently rain will quickly drain and snow will fall from it. Triangular trusses from corners are usually mounted on such buildings.
Cover roofs with such slope angles in most cases with slate or metal sheets. For long spans from 14 m, trusses with descending braces are most often used. Such structures are well tolerated by significant snow and wind loads.
Twin farms
Such systems are often mounted on racks and boxes when the span length 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 trusses, one should, among other things, take into account the fact that both parts must be absolutely identical. I.ehalves should not be divided into left and right. Otherwise, confusion may occur when mounting trusses on the building box.
When assembling such double structures at the top, it is desirable to use, in addition to welding, as many bolted connections as possible. In this case, the knots will be the most durable.
What are Polonceau Farms
Such designs consist of two triangular parts connected by a coupler. The main advantage of such trusses is the absence of the need to use long braces. Thanks to this, the construction is not only strong, but also light.
Such trusses are mounted, as already mentioned, for long spans. Most often they are used in the construction of large industrial buildings.
Timber-metal trusses
In order to save money in the construction of buildings and small architectural forms, among other things, combined support structures can be used. For example, the lower truss tie, racks and puffs are often made from a pipe and a corner, and the upper belt is made from a board or a beam.
Lumber for such structures is chosen well dried and with a minimum number of knots. The moisture content of timber or boards should be no more than 12%. Before using for the assembly of combined supporting structures, it is desirable to dry the lumber for an additional several months. Otherwise, due to shrinkage, the wood in the finished frame may subsequently crack (the metal will retain its dimensions).
Tosuch farms turned out to be 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 connected using epoxy glue. In this case, the reinforcement is passed inside the upper chord (in glued structures).
