The RIDGE is the highest point of the roof.
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The SPAN is normally the width of the building and is measured to the outside face of the stanchions (or columns or uprights). In a portal framed building it is the distance over which the rafters (or roof beams) reach. It is usually more cost effective in a rectangular building to have the span shorter than the length of the building.
Many industrial ans commercial buildings these days are designed and manufactured using cold-rolled steel sections.
Although lighter in weight than hot rolled sections, the cold rolled steel is very strong (the rolling process actually enhances the strength of the steel) and allows a fully-engineered design of frame with lower foundation loadings. In addition, the sections, together with all cleats and brackets, are fully galvanised, which makes the frame virtually maintenance-free.
Cold-rolled steel frames are usually most cost-effective in small to medium-sized buildings (up to 20m span and 6m eaves) and in areas where low foundation loadings are important, while hot rolled frames are more suitable for the larger spans. A further option for larger buildings is a multi-span design, where two frames (either hot or cold-rolled) can be erected in parallel, sharing a central row of columns.
Lightweight galvanised steel frames are fabricated using computer aided manufacturing facilities which makes them suitable for for fast, large volume orders with the added benefit of ‘bolt together’ construction making the system suitable for full relocation.
Large spans can be attained through the fabrication of heavyweight portals constructed from hot-rolled steel sections and steel plate, fitted with fully galvanised steel purlins and cladding rails in the more traditional format.
These tend to be robust structures, being built from standard beams and sections. They are relatively heavy and may require substantial foundations.
Hot-rolled steel frames may also be more suitable for some monoslope designs.
The frames are usually provided primer-painted and normally require finish painting and routine maintenance.
In simple terms a portal framed building is series of rigid frames each comprising two uprights and a cross beam, or more commonly two rafter sections forming a pitched roof. Portal framed buildings can be constructed in reinforced concrete, timber or most commonly in steel. They are a cost effective way of providing clear spans for manufacturing, warehousing and a multitude of uses.
Steel portal framed buildings can be constructed in either cold rolled galvanised steel or using hot rolled ‘heavyweight’ sections and we will discuss the merits of each in later articles.
Details of our own portal framed buildings can be found on this site by clicking here.
