Connecting the costs of a steel frame

How to design the most efficient steel connections:

Despite accounting for less than 5-10% of the frame weight, connections influence between 40-60% of a frame’s total cost (according to the Steel Construction Institute) – a similar proportion to that of the steel itself. So taking the time to understand and carefully design these, and choose their adjoining members, is key.

Steel connections – the structural elements joining the various members within a steel frame – are complex, needing to perform multiple functions. They work to connect and brace primary and secondary members, while also able to transmit the imposed forces and rotations without developing further secondary forces.

Connections with the lowest detailing, fabrication and erection labour content are most efficient.

Understanding steel connections

There are a multitude of connection types or forms, including simple connections – including beam-to-beam, beam-to-column, column splices and base plates – and special connections, such as tube bracing. Simple connections are typically more cost-effective to fabricate, requiring less effort in manufacturing and welding.

Connections can also, broadly, be categorized as ‘pinned’, ‘rigid’ or ‘semi-rigid’ connections, based on their structural performance, and bolted or welded, based on their erection requirements.

Choosing steelwork connections

Which connections are appropriate depends on a number of factors. The key consideration is the internal forces or loads a connection is expected to resist – connections can only be accurately designed with comprehensive information on what is required of the frame.

The types of connections within a steel design must also take into account the size and types of members being connected and the bracing or stiffening requirements of these.

For example, seeking to deliver a lighter frame using light columns and beams to reduce weight will create knock-on costs for more complex stiffeners in the connections. Therefore, increasing the column or beam weights will reduce reliance on, and therefore costs of, the connections required for them.

Connections are a key part of why lighter frames don’t necessarily mean lower overall costs.

Additionally, the fabrication techniques required, such as with or without welding, and the bolt sizes or spacing required, will influence the choices. Connections have a big impact on the manufacturing process and also on the on-site activities. Incorporating connections that negate the need for site welding or blind bolting can allow for a more efficient erection process.

Some steel connections may be designed based on aesthetic requirements too – if a connection and member are to remain exposed for architectural value and visual appeal, for example.

Whichever type is deemed appropriate, all steel connections must also be designed and fabricated according to the steel design Green Books and European standards.

Designing steel connections

To create economies in connection design, standardising connections is beneficial, allowing for reduced costs on materials and fabrication, and then through repetition in erection. This sees bolted connections incorporated into the steel design to remove requirements for expensive on-site welding. These also hold a better lifetime value, able to be dismantled and reused or recycled at a structure’s end-of-life.

Connection design for steel frames should focus on simplicity, symmetry and sensible rationalization. For 5 key details to focus on during design stage, read our article detailling: building on from design conception.

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