Steel erection: sequence, stability and site checks

A typical sequence

1. Foundations and anchor bolts are surveyed: grid lines, levels and bolt projections are checked before any steel arrives.
2. Columns are set on levelling nuts or shims and plumbed.
3. The first braced bay is completed: columns, rafters or beams, roof and wall bracing and the purlins of that bay. It becomes the stable “anchor” for the rest of the building.
4. Further frames are erected bay by bay and tied back to the braced bay with purlins and struts.
5. Secondary steel – purlins, girts, sag rods, flange braces – is completed, then the bracing is tensioned and the structure is plumbed and lined.
6. Bolts are tightened to their final condition, base plates are grouted, and the cladding follows.

Temporary stability comes first

A partly erected frame is weaker than the finished building: the bracing, the diaphragm action of the roof and the restraints from the purlins are not all there yet. The erection method statement, prepared by a competent engineer, defines the crane, the lifting points, the temporary bracing and guys and the order of work. Software can show and simulate the sequence; it cannot decide whether a partial structure is stable.

Inspections on site

• Position against the grid and elevation of the base and top of column.
• Plumbness of columns and alignment of beams and rafters.
• Bolted connections: correct bolt grade and length, washers, tightening method, marking of tightened bolts.
• Site welds, touch-up of coating damage, foundations and anchor bolts.
• Final acceptance by the client or its inspector.

Permitted deviations are given by the execution standard of the project (for example EN 1090-2 or AS/NZS 5131) and the project specification.