Roof trusses characterize the economical use of building materials (timber, steel). Compared to traditional roof constructions, a truss, composed of single lightweight elements, can significantly benefit shipping and assembly. The trusses are more labor demanding and require connecting devices, on the other hand. However, if it is possible to produce more similar trusses, substantial economies of scale can be obtained.
The architectural height of a rod is generally more significant than the height with solid beams of similar constructions. However, this is not typically a disadvantage for roofs as roofs must frequently be taller on the ridge and lower on the eaves depending on the roof cover material, thereby facilitating the draining of the roof and making the watertight.
Truss competitors
While the usage of steel for roof structures requires a truss nearly always, the truss has significant rivals with timber constructions. These are the roofing and the roofing.
The Single Dach
Both rafters and purlins form the purlin roof. Posts support the ridge purlin. The rafters function as basic beams, with or without a lifting device between the purlins.
The roof of the raft
The roof of the rafter comes from the building of the tent. It comprises two beams and a beam, forming a triangle. Therefore, the simplest form of the roof is the same as the fundamental element of the roof. With a collar beam close to the ridge, the rigidity of the rafters may be enhanced. Typically a bevel shoulder connects the rafters with the tie beam. This had the drawback that the slope of the roof was not even but was flatter at the base of the roof to fit the shoulder of the bevel. Steel connections are frequently utilized today, with consistent roof pistes. The rafters can alternatively be placed on a concrete plate to replace the tie beam.
The table below shows the principal elements and the advantages and disadvantages of the three basic roof structure design alternatives. It can help designers pick the best roof structure for a particular application.
Note, big hangars and lobbies are not taken into account.
The Dead Loads
There are two different load types on trusses: dead load and live load.
Distance between the trusses
For steel and wood buildings, the variables that regulate the separation of individual roof trusses are different:
Timber:
Timber boards and bars are only available in sizes from 150 to 200 mm in width and height. The most affordable spacing of wooden trusses is between 1.5 and 2.0 m with the specified loading capacity of wood.
Steel:
Usually, small roof trusses without cranes will be set up. The weight of each coupling consequently limits the spacing of steel couplings (or portions of it, if assembled on-site). The examples of the stainless steel trusses given in this handbook do not exceed 3 kN per truss.
Last Words
The size of purlins is the other issue to take into account. Purlins are made from equals angle bars or sections C for the tiny roofs covered with MCR or steel roofing (where available). Purlins for the roofing system are 400 mm apart. The entire length of purlins required is frequently several hundred meters of steel sections, even for modest structures (8 to 15 m). To produce an economical construction, Purlins should preferable be light sections.
