Introduction
Fabrication
Steelwork is fabricated in a factory into components. It is then erected on site into a complete assembly, ready to take floors, walls, cladding and roof. The material is generally obtained from rolling mills and stockists in the form of I sections, channels, hollow sections, angles or plate. These have to be cut to length, drilled and welded as necessary ready for assembly, and in most cases some protective treatment will be applied against corrosion. All such operations come under the heading of fabrication.
Erection
Once the pieces have been fabricated they are transported to site and connected together to make the framework which forms the 'skeleton' of the building. This process is known as erection. To take full advantage of the benefit of speed of construction which steel offers, it is necessary to:
· order the material sufficiently in advance
· avoid any change to the information supplied to the fabricator at the outset
· prepare the site in good time to receive the steel frame.
The steel erector will wish to see the steel erected in one continuous smooth operation.
Usually a frame is erected on concrete foundations provided by another contractor. The main contractor and the steel erector strive to ensure that the steel frame can be erected in a continuous operation. The erector should not have to leave the site and return later to complete the work, and the construction of the whole building should be planned to allow other trades involved to follow-on as rapidly as the steel erection will allow. If, for example, a section of the frame is sufficiently advanced to allow suspended floors to be laid, areas below those floors will be relatively protected from the weather, and fitting-out can proceed in the dry.
Steel construction is usually based on standard sections, but these can be modified to create new shapes.
There is a wide range of standard steel sections produced from which designers will determine the profile, size and weight appropriate for the majority of situations.
As a general rule in steel construction, material is cheaper than labour. It is therefore often economic to use a greater weight of steel if the amount of labour is thereby reduced. For this reason standard cross-sectional shapes are normally used and account for the major proportion of steel used for building frames. However, there are circumstances where modified forms of cross-sectional are preferable.
