Purpose and material of metal trusses
A metal truss is a finished or assembled welded( less bolted assembly, riveting) rafter construction. In the usual interpretation of metal triangular trusses called flat element, which includes only the supporting parts of the future roof( actually carrying slopes, legs, struts, crossbars, etc.).According to another version - the same rigid truss triangle, tied to the lower belt, with installed braces and racks.
Actually, the purpose of such constructions is easily read in their definition. Quick installation of the roof of any industrial building or apartment house with a minimum of labor for planning and arranging the truss system. With the correct calculation of the metal truss from the profile pipe and the qualitative execution of the welding work, further roofing works are minimized: flat pipe assemblies should only be raised on the upper piping of the structure and installed by marking.
The main material is mostly black or galvanized steel in the following rolling variants:
- profile pipes, we already talked about excellent mechanical properties;the choice of a square or rectangular section for a farm depends on how correctly it was calculated;
- T-bar, roof channel with special loads;The weight of such all-metal assemblies is much larger, therefore the scope of application is limited to production construction;
- corner: the opposite version of the manufacture of metal trusses for temporary or economic buildings( awnings, garages, household blocks, etc.), which you can do yourself and yourself with the availability of welding equipment.
For the manufacture of finished trusses for lightweight roof coverings, for example polycarbonate, aluminum profiles are sometimes used, which greatly simplifies the installation of finished products.
How to calculate and select a metal truss
First you need to refer to the technical conditions of the use of rafters, where the two most important parameters are determining: the angle of inclination and the width of the span. Depending on these values, not only the cross-section of the supporting pipes is selected, but also the type of metal construction. To entrust the design and manufacture of such serious constructive elements, we recommend a professional, but to have about them the most general representations are necessary.
There are only four basic construction variants of metal girders for gable roofs:
- a classic triangle on rafter rails;
- triangular construction on the frontal cuts;
- pentagonal segment element with additional ribs;
- polygonal version for spans over 24 meters with potentially high external loads.
Accordingly, the choice of the scheme is set by the project task.
- The slope of the gable roof 22-30o is an ideal variant, which allows to mount the products of the first category in the size range of 6 to 12 m without any problems. The ratio of height and width is assumed to be 1/5.
- Slope roofing should be reduced to 15-22o with the same distribution of metal trusses along the length: the problem solved by the broken line of the lower belt and the corresponding increase in rigidity of the rafter.
- With small roof slopes it makes sense to use single-track trapezoidal trusses whose height along the top edge should be calculated from a ratio of 1/7 or even 1/9 of the width of the room to be covered.
Drawbacks of
steel profile pipes It is clear that manufacturers of such products take over the manufacture of metal trusses according to the parameters of the construction you specify or calculated by the architect, and in market conditions they can offer a range of services from which the head will spin. But there is no product without hidden flaws, such are the laws of the market.
What we have in real life:
- Metal trusses can weigh up to 5 tons even when manufactured from a thin-walled steel profile on a 15 m ceiling. Recalculate the dimensions of your home and think about the delivery. Take into account the linear dimensions of the product. Professional calculation, assembly, transportation and loading-unloading of steel structural elements flies in a pretty penny.
- Installation of the rafter system: no special lifting equipment and welding equipment is indispensable, and good specialists still have to be looked for.
- Finally, without special anti-corrosion treatment, metal trusses from a profile square steel pipe will begin to rust in two to three years from the elementary accumulation of condensate in the attic zone.
But a spoonful of honey still is: such rafters under any external and internal conditions of exploitation will survive not only you, but your home.
