What a welded joint gives you
Continuity. Load transfers across the whole weld length rather than through discrete bolts. The result is a stiffer frame with fewer connection elements.
Appearance. On exposed architectural steel, a welded and dressed joint reads as a single piece of metal. A bolted connection, however neat, reads as an assembly.
Fewer parts. No plates, no packs, no bolt schedules, nothing to come loose.
Why it belongs in a workshop
Weld quality depends on things a site cannot reliably provide: clean, correctly prepared edges; comfortable working position; shelter from rain and wind; and consistent power.
In the shop, a joint can be positioned so the welder works downhand, the material can be cleaned properly, and fixtures hold everything in place. On a wet site, overhead and out-of-position welding in poor light is where defects come from.
This is why most real structures are welded sub-assemblies with bolted site connections. The split is a practical one rather than a preference.
Distortion
Welding heats metal locally and it shrinks as it cools. Weld one side of a member and it pulls that way.
Controlling it is a planning exercise:
- sequence — alternating sides, working from the centre outward
- balanced heat input — not depositing all the weld in one area
- fixtures and jigs — holding members in position while they cool
- pre-setting — deliberately setting a member off-straight so it finishes straight
Straightening a distorted member afterwards is possible and always worse than not distorting it. On long members and on machined assemblies where tolerances are tight, this planning is the difference between a fit and a fight on site.
Material differences
Steel. The most forgiving. Well-understood processes, wide tolerance for technique.
Stainless. Higher thermal expansion, so more distortion for the same heat input. It also needs the weld area cleaned and re-passivated afterwards, or the joint becomes the place corrosion starts — which defeats the point of using stainless.
Aluminium. High thermal conductivity, a tenacious oxide layer that must be removed immediately before welding, and a heat-affected zone where strength is reduced. It needs different processes and considerably more skill.
Finishing a weld
On concealed structural work, a sound weld is enough. On exposed architectural work it is ground flush and dressed so the joint disappears.
That work has to be planned for, because grinding a weld after galvanising removes the protection locally. The sequence is fabricate, dress, then coat — see steel fabrication for how coating specification interacts with that.