Bolted or welded connections on site
Both work. They differ in what they demand from the site, the programme and the inspection regime.
Most frames use both, and the split is usually decided at detailing rather than on site. Understanding the trade-off explains why.
Bolted connections
Faster to make, less sensitive to weather, and easier to inspect — a bolt is either tightened correctly or it is not, and the check is quick. They need accurate hole positions, which pushes the difficulty back into fabrication where it is easier to control.
They are also more forgiving of site conditions: no power requirement at height, no preheat, no protection from wind and dust.
Welded connections
Used where a bolted connection would be bulky or where continuity is needed. On site, welding brings requirements bolting does not: a qualified welder for the procedure being used, control of conditions, and non-destructive testing to demonstrate the result.
Wind and airborne dust both matter in the open here, and they are practical constraints rather than theoretical ones.
How the choice is usually made
- Bolt where the connection allows it, especially at height and in exposed positions
- Weld where the connection demands it, or where fit-up has to be adjusted on site
- Weld in the shop rather than on site wherever the design permits — conditions, access and inspection are all better there
Inspection
Whichever is used, the connection is not complete until it has been checked and the check recorded. For bolts that means verified tightening; for welds, visual inspection and whatever NDT the specification calls for. A frame with no inspection record has no demonstrable capacity, whatever it looks like.