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182 Barry’s Advanced Construction of Buildings
Base plate welded to column
Dished packing piece placed between
bolts fixes column at correct level and
allows movement
Void formed by cardboard or
polystyrene cones, which allows
±20 mm horizontal tolerance is filled with
grout
Large washer fixed to bolt to prevent
pull out
Pad foundation
Figure 4.26 Pinned base to steel portal frame.
holding-down bolts to the foot of the portal frame as illustrated in Figure 4.26. The packing
between the plates allows some flexure of the portal post independent of the foundation.
Short-span portal frames are usually spaced between 3 and 5 m apart and medium-span
frames at between 4 and 8 m apart to suit the use of angle or cold-formed purlins and
sheeting rails. Long-span portals are usually spaced at between 8 and 12 m apart to economise
on the number of comparatively expensive frames. Channel, Zed, I-section or lattice
purlins and sheeting rails support roof sheeting or decking and wall cladding. With flat
and low-pitch portal frames, it is difficult to achieve a watertight system of roof glazing;
therefore, a system of monitor lights is sometimes used. These lights are formed by welded,
cranked I-section steel purlins fixed across the portal frames (Figure 4.27). The monitor