The roof truss is a popular roofing option that a number of modern homes are now sporting. There are two general types of trusses: the wood truss and the steel truss. Wooden trusses are commonly used on residential homes while steel trusses are often found on a majority of new commercial buildings. Prefabricated steel trusses are light-weight systems known for their high strength and are capable of taking much more load than the common wood truss.
There are some basic facts that one needs to know about any roof truss. The truss derives its strength from the arrangement of the triangles which make up the truss itself. The top chords of the truss are constantly in compression and as such, they push out at the heel as well as down at the peak. On the other hand, the bottom chord is in tension. As such, it is capable of resisting outward thrust. The webs of any truss design form smaller triangles which strengthen the overall structure and ensure that the truss system is rigid. Due to the unique design of the truss, the loads exerted on the truss system can either be compressive or tension.
There are many different types of steel trusses. Common trusses include the Scissors truss, the Attic truss, the Cantilever truss and the Hip Step down truss. Most roof truss designs have webs that run at a specific angle between the top and bottom chords. However, there are some exceptions such as the Gable-end truss which has webs that run vertically. As such, this truss design sits atop the building’s end walls and looks very much like part of the wall rather than a separate truss structure.
When specifying the type of steel truss you would like to have, there are certain inputs required by the manufacturer. These include the truss type, the location, span, pitch and building category. Specifying the truss type is based on whether or not you would like storage or living space. Moreover, in this category, architectural details i.e. overhang and tail lengths are also defined. The building category determines the type of structure the truss is intended for i.e. whether hospital, school, etc.
It is important to note that the pitch of the truss will influence a number of design parameters. Moreover, the desired pitch will also have an impact on the overall weight of the roof truss.
Moreover, there are optional inputs such as the wind exposure category and the open category which determines the proportion/ratio of doors and windows to the total wall area.
Steel roof trusses are basically assembled on large metal tables. These tables feature clamps and pins which hold the truss sections in place. The chords and webs of the steel truss are placed in a jig and once the jig has been completed, the truss is loaded directly onto the delivery truck. When the steel trusses are hauled, the top of the truss is secured by a light gauge track or stud.
Truss installation is a crucial stage that cannot be overlooked. When installing trusses, they should never be attached rigidly to the interior of the partitions. By doing so, bending forces will be induced on the truss and these structures aren’t designed to bear such forces. Secondly, your truss installer should always follow the instructions as laid out by the truss manufacturer. Thirdly, and probably the most significant, is one should never attempt to modify or cut trusses before seeking expert engineering advice.
The main drawback to light-gauge steel trusses is their cost. These trusses are more expensive than their wooden counterparts which still dominate in many residential properties. However, light-gauge steel trusses are gaining ground thanks to their numerous benefits i.e. greater free spans and the ability to carry much more load.