Structural Steel and Platework
The governing documents
CSA S16 governs steel structures, CSA W59 governs welding of steel structures, and CSA W47.1 certifies the fabricator. Bolts are ASTM F3125 (A325 and A490 grades). Connections use standard, oversize, short-slotted or long-slotted holes, and the permitted type depends on the ply and connection category.
Bolting
- Turn-of-nut requires a snug-tight condition first, then a specified rotation; the nut is turned, not the bolt, unless the procedure states otherwise.
- DTI washers are compressed to a specified gap; a tension calibrator (Skidmore-Wilhelm) verifies the method and the actual bolt lot.
- Calibrated wrench torque is valid only for the lot tested; impact wrenches need verification.
Erection tolerances
Column plumbness is commonly limited to 1:500 of height, with separate limits for elevation, alignment and camber. Base plates are shimmed, plumbed and grouted after the frame is aligned and bolted; grout is not a shim.
Worked example: is the column acceptable?
A 9 m column reads 15 mm out of plumb at the top. Tolerance = height ÷ 500 = 9000 ÷ 500 = 18 mm. The column is within tolerance and is accepted and recorded, but the next member's alignment still has to be checked because errors accumulate across a bay.
Platework
Tanks, bins, hoppers, chutes, stacks and ducts add stiffeners, girts, wear liners and gussets to the same rules. Distortion is controlled by sequencing: weld from the restrained centre outward, balance heat about the neutral axis, and leave the closing seam until last. Weld shrinkage bows a stiffened panel, so preset and sequence rather than fight it afterwards.
Traps
- Tensioning a connection and then welding it, or the reverse, without engineering direction.
- Using oversize or slotted holes in a bearing connection where they are not permitted.
- Designing for shear but loading the bolts in tension.
- Treating mill tolerances and fabrication tolerances as the same thing - they stack.