Steel connections
What a joint transfers, and the support condition it actually delivers on site.
The sizing asks for a support condition as though it were a setting. On paper it is; on site it is a promise about what gets welded and bolted. A beam sized as fixed and laid on a corbel is sized for a moment nothing carries.
Bearing support
Simple bearing (beam on corbel/masonry)
The beam simply rests on a support (concrete corbel, masonry padstone or steel bracket), often via a seating plate and an elastomeric pad. Only the vertical reaction is transferred; rotation and slight expansion remain free. Common when a steel roof rests on blockwork or concrete walls, a very frequent case in Africa.
Delivers the support condition Simply supported
Components
- Grouted seating plate
- Elastomeric pad or bituminous felt
- Bearing length ≥ 100 mm
- Uplift anchorage (wind!)
Common mistakes
- Forgetting wind uplift anchorage (light roofs blown off!)
- Insufficient bearing length → local masonry crushing
- No bond beam under the support
When to use it Trusses or purlins on masonry walls, footbridges, floor beams on concrete walls.
Pinned connection
Pinned connection (double angle cleats)
A pinned connection transfers shear only: rotation stays free. The beam is fixed to the column web with bolted angle cleats. It is the most economical and common connection for secondary beams, but the structure must then be stabilized by bracing.
Delivers the support condition Simply supported
Components
- 2 angle cleats (e.g. L 80×80×8)
- 1 bolt row per leg (M16-M20)
- Erection clearance (~2 mm)
- Optional beam flange cope
Common mistakes
- Assuming it stabilizes the frame (it transfers no moment!)
- Overly stiff cleats creating parasitic moment
- Forgetting the building's overall bracing
When to use it Secondary beams, joists, braced structures, fast site erection with tolerances.
Rigid connection
Moment connection (extended end plate)
A moment connection transfers both shear forces AND bending moment between beam and column. Relative rotation is prevented: beam and column deform together. It is the key connection of moment-resisting frames (portal frames without in-plane bracing).
Delivers the support condition Interior span
Components
- Extended end plate (15-25 mm)
- 2 rows of preloaded HR bolts (M16-M24)
- Column web stiffeners
- Optional haunch (tension zone reinforcement)
- Beam-to-plate fillet welds
Common mistakes
- Omitting column web stiffeners (local crushing)
- Ordinary bolts instead of preloaded HR bolts
- Plate too thin → 'book-opening' deformation
- Ignoring the compression zone check
When to use it Portal frames, moment-resisting frames, structures where deflections must be limited and in-plane bracing avoided.
Truss node
Gusset plate (lattice truss node)
The gusset is the plate joining chords and diagonals at a lattice truss node. Members, loaded in pure tension/compression, are bolted or welded to it. Golden rule: member axes must converge at a single point (workline layout) to avoid parasitic moments.
Delivers the support condition Member to member: it decides no beam support condition.
Components
- Gusset plate (8-15 mm)
- Angles or tubes (diagonals/verticals)
- M12-M20 bolts or welds
- Converging axes layout
Common mistakes
- Non-converging axes → parasitic moments and cracking
- Single bolt per member (unwanted rotation)
- Slender gusset → local buckling
When to use it Roof trusses, lattice girders, bracing, towers, wherever members meet at a node.
Column base
Pinned column base
The column is welded to a thin base plate fixed with 2 anchor bolts on the column axis. The base transfers axial and shear forces but no moment: the foundation stays small and economical. Horizontal stability must come from elsewhere (bracing, frame fixed at the top).
Delivers the support condition Simply supported
Components
- Thin base plate (12-20 mm)
- 2 anchor bolts M16-M24 on axis
- Non-shrink grout bedding (30-50 mm)
- Optional shear key
Common mistakes
- 4 corner bolts on a thick plate: it becomes an uncalculated fixed base!
- Skipping the grout bedding
- Anchor bolts too short (embedment length)
When to use it Braced buildings, cladding posts, light structures, weak soils (smaller foundations).
Column base
Fixed column base
Thick base plate, 4 corner anchor bolts and stiffener gussets: the base transfers a bending moment to the foundation. The column then contributes to horizontal stability (cantilever mast, portal). Trade-off: a significantly larger foundation block.
Delivers the support condition Interior span
Components
- Thick base plate (20-40 mm)
- 4-8 corner anchor bolts
- Vertical stiffener gussets
- Foundation sized for overturning
- Non-shrink grout
Common mistakes
- Undersized foundation → overturning
- Ignoring bolt tension (pull-out)
- Plate without gussets → excessive plate bending
When to use it Moment frames, cantilevered canopies, masts, crane buildings, structures where bracing is impossible.
This page classifies joints, it does not design them. Bolt, weld and plate sizing belong to EN 1993-1-8, which this product does not implement.