Steel trusses

All About Steel Trusses

Structural steel trusses are the metallic support mechanism, found under the roof to provide support. Generally, roof trusses are made out of two materials, steel and timber. Trusses made out of steel structures are a common choice among commercial, industrial and large residential complexes. It is one of structural engineering's most important and iconic elements. Made of individual members with equal counteracting tensile and compressive forces, its purpose is designed to behave as a single object which carries/supports a load over a span.

Trusses are used in a broad range of buildings, mainly where there is a requirement for very long spans, such as in airport terminals, aircraft hangers, sports stadia roofs, auditoriums and other leisure buildings. Trusses are also used to carry heavy loads and are sometimes used as transfer structures.

 Trusses comprise assemblies of tension and compression elements. Under gravity loads, the top and bottom chords of the truss provide the compression and tension resistance to overall bending, and the bracing resists the shear forces advantage of the truss design for roofs is that ducts and pipes that are required for operation of the buildings services can be installed through the truss web, i.e. service integration.

Although joints in trusses are often hardly pinned in reality, it is generally satisfactory (and encouraged by design Standards) to assume the joints are pinned and to verify the members for axial load only. If loads are applied between nodes, trusses are often analyzed with continuous chords, but with all internal members pinned. These assumptions about pinned joint behavior apply to both bolted and welded connections. Where member centre lines do not intersect at a node (the joint geometry may have been adjusted to increase the strength of the joint), the additional moments produced by the eccentricity are usually allowed for in the design of the chord members.

In order for a connection with clearance holes to transmit the load, the bolt must come into contact with one or other of the connected parts which allows slip in the connection. For a connected tension member, this slip can be considered as an additional extension that is added to the elastic elongation of the member in tension. Likewise, for a connected compression member, the slip is considered as a reduction in length that is added to the elastic shortening of the compressed member. The total slip in the many different connections of a truss structure can lead to a significant increase in displacements, which can have more or less serious consequences.

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