Preparation of steel work for erection is called as fabrication. It includes all works necessary to layout, cut, drill, rivet or weld the steel sections. The fabrication has to be properly planned such that the work at the site of erection should be reduced as much as possible. Thus most of the work is carried out in the fabrication shop itself.
All materials procured from the mill or the markets are straightened if necessary. Cutting is effected by shearing, cropping or sewing. For mild steel gas cutting by mechanically controlled arcs is also used. For high tensile steel gas cutting is permitted under special care. Plates and angles are cut by shearing. Beams and channels are usually cut to the desired lengths in factories.
Templates according to the shape of the final job are prepared. Templates may be made of wooden strips showing location of all holes and cuts. Cardboard templates may be used for gusset plates.
All the materials are laid out. The centres of the holes are identified with a punch. Holes are drilled, punched or bored. Drilling is generally preferred as it gives the exact hole without spoiling the surroundings. For thick sections drilling is preferred.
When the components of a member are ready, they are held in position temporarily by shop bolts. Shop bolts are longer in size than the normal ones. There should be at least two bolts put in one part of a member. All assembled parts should be in close contact. Further all bearing stiffeners should bear tightly at top and bottom. In general, no drifting should be permitted.
Assembled parts are then riveted adopting hydraulic or pneumatic pressure. Rivets of diameter less than 10 mm are driven cold. Bigger rivets are heated by a steady flame produced by burning oil or using electric heaters. It is the practice that the rivet fills the hole fully and forms a head of standard size. While riveting, if loose, burnt or badly formed, rivets should be cut out and replaced.
After finishing the required structure formation, it is cleared thoroughly and one coat of red lead paint is given. All machined faces should be coated with a mixture of white lead and tallow. All inaccessible portions of the structure should be painted with two coats of read lead paint.
The completed work should be temporarily shop erected such that accuracy of fitness may be checked before despatch.
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