A steel frame is only as strong as its joints. Connections also drive a large share of fabrication and erection cost, so choosing the right type matters for both safety and budget. This guide sorts steel connections by how they behave, how they are fastened, and the details you will see most often on drawings.
By behaviour: simple, rigid and semi-rigid
- Simple (pinned) connections pass shear from the beam to the column but allow the beam end to rotate. They are cheap and quick to erect, and the frame then needs bracing or cores for stability.
- Rigid (moment) connections pass bending moment as well as shear, holding the angle between beam and column. They make the frame stable without bracing but need more plates, bolts and welding.
- Semi-rigid connections fall in between. They are used less often because the analysis must account for the joint’s actual stiffness.
By fastener: bolted and welded
Bolted connections are quick to make on site and need no specialist site welding. Common bolt grades are 8.8 and 10.9 under British and European standards, or ASTM F3125 grades A325 and A490 under AISC. Bolts can work in bearing, or be preloaded so the joint resists load through friction, which is used where slip or reversing loads are a problem.
Welded connections are made mostly in the fabrication shop, where quality is easier to control. Fillet welds suit most plate-to-member joints; full penetration butt welds are used where the full strength of a plate must be developed. The usual approach is shop-welded, site-bolted: plates are welded on in the workshop and the members are bolted together on site.
Common connection details
- Fin plate (shear tab): a single plate welded to the column, bolted to the beam web. The standard simple connection.
- Double angle cleat: two angles bolted to the beam web and the column.
- Flexible end plate: a thin plate welded to the beam end and bolted to the column.
- Extended end plate: a thick plate projecting above the beam, with bolts outside the flange. A common moment connection.
- Haunched connection: a deepened beam end at the eaves and apex of portal frames.
- Column and beam splices: joints that join members too long to transport in one piece.
- Bracing connections: gusset plates that bring diagonal braces into the beam-column joints.
- Base plates: plates at the column foot with anchor bolts into the concrete, designed as pinned or fixed.
How connections are designed
Each connection is checked for every way it could fail: bolt shear and bearing, weld strength, plate bending, block tearing, and local failure of the column, such as web crushing or panel shear, which may call for stiffeners. Software such as IDEA StatiCa now models the whole joint with finite elements, which helps with complex geometry that hand methods struggle with.
On many UAE projects the consultant gives the member sizes and forces, and the connection design is then passed to the steel fabricator’s engineer. The calculations and connection drawings go back to the consultant for approval before fabrication starts.
From our work
Recent connection work by our team includes the anchorage connections for the Brazil Pavilion at Expo 2020 and the connections for a steel gridshell in Dubai Media City, where every node had a different geometry.
Related
Steel connection design · Shop drawings and details · Bracing in steel structures
Need help with your project?
Wrenze Steel Engineering Consultancy designs steel structures for contractors, fabricators and consultants across the UAE. Request a quote or call +971 54 358 2558 or email info@wrenze.com.