Basic erection planning
In principle, steel erection involves positioning, aligning and securing the components on prepared foundations to form a complete frame.
Steel erection consists of four main tasks:
· Establishing that the foundations are suitable and safe for erection to commence.
· Lifting and placing components into position, generally using cranes but sometimes by jacking. To secure components in place bolted connections will be made, but will not yet be fully tightened. Bracings may similarly not be fully secured.
· Aligning the structure, principally by checking that column bases are lined and level and columns are plumb. Packing in beam-to-column connections may need to be changed to allow column plumb to be adjusted.
· Bolting-up which means completing all the bolted connections to secure and impart rigidity to the frame
The procedures can be illustrated for a skeletal steel frame
Careful planning is necessary to realise the advantage of speed offered by steel construction.
There are three main planning factors that affect the buildability of the scheme. These are:
· Practical erection sequence. The location of bracing or other means of maintaining structural equilibrium are crucial here.
· Simplicity of assembly. Simply-assembled connections are the main factors here.
· Logical trade sequences.
Site work tends to be labour intensive and hence relatively expensive and the primary aim of the programme should be to minimise costs by shortening the time on site.
The principal design factors contributing to buildability are:
· Repetition and standardisation. There are two aspects to standardisation: repetition of the same building type (eg the portal shed) and common/standard details for connections.
· Achievable tolerances. If 'tight' tolerances are specified too tight, then special controls will be needed and possibly specially-engineered details.
· Frame type. Here, the primary choice is between simple and rigid-jointed frames, the former being much quicker and easier to erect.
· Floor systems. For multi-storey frames, the choice of floor system will affect the erection sequence as it determines the stability of the part erected structure, and how quickly other trades can follow-on.
