Steel construction owes its speed to the fact that most of it is fabricated in the workshop. But that speed only exists if erection was thought through during design. A perfectly calculated frame that cannot be lifted in the intended order costs more than an ordinary frame properly sequenced.
Split the structure around the lift
The question is not only “what sections?” but “what lengths?”. Transportable length, the capacity of the available crane, laydown space and site access all determine where the splices go. An extra connection costs workshop time; a member that cannot be delivered costs far more.
A steel frame is drawn twice: once to stand up, once to be buildable.
Temporary stability is not final stability
A steel frame stands through its bracing. That bracing is only complete once erection finishes. Between the first frame lifted and the last tie bolted, the structure passes through states in which it is considerably more vulnerable, particularly to wind.
Those temporary states are checked and propped. Guys, erection bracing, an imposed lifting order: these are design outputs as much as member sizes are, and they belong on the erection drawings rather than being improvised on site.
Tolerances meet at the interfaces
Steel is fabricated to the millimetre; concrete is poured to the centimetre. Where they meet — the holding-down bolts cast into the bases — is where those two worlds must reconcile. It is the most ordinary cause of delay on a steelwork site.
- Setting-out of bases and bolts surveyed and approved before fabrication
- Slotted holes and base plates sized to absorb the permissible deviation
- Lifting order and temporary stability shown on the erection drawings
- Workshop welds inspected according to how critical they are
- Preloaded bolt tightening verified and recorded
- Corrosion protection matched to exposure, made good after erection
Corrosion is dealt with upstream
The protective system depends on how aggressive the environment is: a shed inland and a building by the sea require neither the same surface preparation nor the same coating thickness. That choice is made during design, because it determines workshop preparation.
Which leaves the point most often forgotten: making good after erection. Lifting and bolting inevitably damage the coating. Without careful touching-up at contact points and connections, corrosion starts exactly where the structure is most heavily worked.
