What is a steel connection?
A steel connection is the point where steel members such as columns, beams and bracing are joined with bolts or welds so that they transfer forces to each other. The connection partly determines how the whole structure behaves. Design follows Eurocode 3, Part 1-8 (EN 1993-1-8).
Types
By fastening method
– Welded. Fillet welds and butt welds give a stiff, compact joint. Welding is preferably done in the fabrication shop, where conditions and inspection are better.
– Bolted. On site, connections are mainly bolted, so erection is fast and needs no welding equipment. Bolts of property class 8.8 and 10.9 are common. A typical combination: plates welded to the member in the shop, bolted together on site.
By behaviour
– Pinned (simple). The joint mainly transfers shear and allows rotation. Examples: a fin plate, web cleats or a partial-depth end plate. Stability must then come from bracing, walls or floors.
– Moment-resisting (rigid). The joint also transfers bending moments, for example with an extended end plate, column stiffeners or fully welded flanges.
| Pinned (simple) | Mainly transfers shear and allows rotation. Examples: fin plate, web cleats or partial-depth end plate. Stability must then come from bracing, walls or floors. |
|---|---|
| Moment-resisting (rigid) | Also transfers bending moments. Examples: extended end plate, column stiffeners or fully welded flanges. |
Common details
– End plate. A plate on the end of a beam, bolted to a column or another beam.
– Base plate. A plate under a column, fixed to the foundation with anchor bolts. After levelling, the gap underneath is filled with grout.
Application
- Follow the drawing exactly. Bolt diameter, property class, number of bolts and weld sizes are calculated. Never swap a bolt for a weaker one.
- Tighten bolts as specified. Preloaded connections require a prescribed tightening method; the thread must protrude fully through the nut.
- Don’t drill, flame-cut or weld existing steelwork without the structural engineer’s approval.
- Take care with galvanised steel. Welding galvanised steel releases harmful zinc fumes; use extraction and repair the coating afterwards.
- Grout base plates fully, without voids, so the column bears evenly.
Common mistake: removing a wall or brace during alterations to a steel frame with pinned connections. Those joints provide no stability themselves, so the frame can become unstable.
Related terms
- Welding
- Structural steel sections
- HEA beam and HEB beam
- Column
- Beam
- Pinned support
- Casting mortar
- Composite steel deck floor
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