Erection is the stage where earlier mistakes turn into visible cost, and where new mistakes turn into danger to life. This article explains the sequence as it should happen, and the points that separate an organised site from one waiting for an accident.
Note: The safety measures described here are general and do not replace a written, project-specific safety plan compliant with the regulations in force at the site.
1. What must be finished before the first member arrives?
A good deal must be finished before steel enters the site: levelling and access roads that will take trucks and cranes, a defined level storage area, power and water, and a review of the site layout for lifting positions.
And correct storage is an underrated item: members are stored on raised bearers, clear of ground contact and water, with a slight fall to shed rain. A carefully fabricated member left on wet ground for two weeks arrives at erection with its surface protection already degrading.
One decisive logistical item: shipping order matched to the erection sequence. Members arriving in random order produce site chaos, coating damage from repeated handling, and lost crane time.
2. Why are anchor bolts the most sensitive item?
This is the single greatest cause of stoppages. The structure is fabricated to millimetre accuracy and the foundations built to centimetre accuracy — and the meeting point between them is the anchor bolt group.
A few centimetres of displacement in a bolt group means either a field modification to a fabricated member — which we dislike, because it compromises surface protection and accuracy together — or breaking out and recasting.
The prevention is well known and simple: setting-out templates that hold spacing and squareness, a dimensional survey before and after the pour, and templates fixed firmly enough not to shift during pouring and vibration. Ten minutes of survey saves a week.
3. What is the correct erection sequence?
Erection follows a defined sequence that is not improvised:
- Survey and check anchor bolt positions against the drawings.
- Raise the first two frames and hold them with temporary props and guys.
- Install the bracing between them to form a self-stable bay.
- Advance frame by frame, each tied back to the stable work behind it.
- Purlins and secondary connecting members.
- Cladding, then doors and openings.
A practical note: the first stable bay is the alignment reference for everything after it. An error in its squareness propagates and accumulates along the length of the building.
From our projects: the most demanding sequence we have run was three adjoining hangars on an operating factory roof — spans of 21, 14 and 14 m. Erecting over a working roof constrains crane positions and lift order, and leaves no room to defer the permanent bracing between one hangar and the next.
4. When does the most dangerous moment of erection happen?
There is one moment in which most of the risk of this stage concentrates: releasing the temporary support.
The iron rule: temporary support is not released before the permanent bracing system is complete. Most partial-collapse incidents in this sector happen at precisely that moment — a structure that looks standing and complete while in fact depending on a temporary prop, which is removed to speed the work, and it comes down.
The reason is that before bracing is complete the structure has no resistance to horizontal forces: a moderate gust, a crane knock, or even a worker's weight on an untied member is enough.
5. What lifting and safety requirements apply on site?
What separates an organised site from the rest:
- A considered lifting plan with known weights and centres of gravity for each member — not visual estimation.
- Loads rigged with sound, inspection-certified equipment, and lifting points defined on the fabrication drawings.
- Work at height under fall-arrest systems, not reliance on care and experience.
- A closed lifting zone that nobody enters during a lift, and no load travelling over anyone.
- Stopping work at wind limits — cranes have a stated operating limit, and wide flat members behave like sails.
6. How is bolt tightening torque controlled?
Bolted connections are what hold the building together, and tightening them is not a matter of arm strength. Torque is set with calibrated wrenches and documented — because an under-tightened bolt slips, and an over-tightened one can fail by over-extension.
And the programme needs a later review: bolts in members subject to vibration lose part of their tension in the first months, and reviewing their tightness is a permanent item in the maintenance plan rather than a one-off.
7. How are coatings touched up on site?
Every location scratched or welded on site needs treatment: cleaning the area, removing any rust that has appeared, and rebuilding the coating system to the required thickness.
This item is often forgotten because it falls at the end of the work when time pressure peaks. But site weld locations specifically are the first thing to rust in a building, because the heat destroyed the protection around them completely.
8. What must be checked before handover?
Before the building is accepted, these are completed:
- A conformity checklist covering dimensions, squareness and floor levels.
- An operating test of doors and moving openings.
- A water-tightness test of the roof, preferably before anything sensitive is installed beneath it.
- Documented bolt torques at critical connections.
- The project file: as-built drawings, mill certificates, inspection reports, maintenance instructions, and the positions of roof penetrations.
The file is part of the handover, not a favour: in five years, when you need to hang a new load, cut a door, or trace a leak, that file is the difference between a decision based on information and one based on guesswork.
- Erection sequence
- Anchor bolts
- Safety
- Handover
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