How Should the Joint in a Cranked Beam Be Made?

A cranked beam is one that changes direction at a point along its length — for example, where a beam must step up or down to match a change in soffit level, or where it must pass around a chimney breast. The crank (the change-of-direction point) is a structural discontinuity that requires careful detailing.

The Required Joint Type: Full-Strength Butt Weld

The joint at the crank point must be a full-strength butt weld, executed in a fabrication workshop by a coded welder.

A full-strength butt weld is one that develops the full tensile, compressive, and shear capacity of the connected members — not just a fillet weld at the surface. It requires:

– Complete joint penetration through the full thickness of the flanges and web
– Pre-weld preparation (bevelled or squared joint faces as appropriate)
– Execution by a welder qualified to the relevant welding standard (BS EN ISO 9606)
– Post-weld inspection (visual, and dye penetrant or ultrasonic if specified)

The weld must be tested to the relevant British and European standards (BS EN 1090 series).

Why This Cannot Be Done on Site

Full-strength butt welds require controlled conditions: a fixed welding position, proper joint preparation, pre-heat where required by material thickness, and accurate distortion control during cooling. These conditions do not exist on a construction site.

Attempting a crank joint on site risks a weld that looks complete but lacks the through-thickness fusion needed to develop the full section capacity. This is a structural failure risk.

Advance Planning

If your project has a cranked beam and you need to bring the beam through a restricted access point (e.g. a narrow door or up a staircase), plan ahead with your fabricator. If the beam must be delivered in shorter sections and joined on site, a cranked arrangement may not be achievable — an alternative structural solution should be discussed with PorthouseDean via a Change Request.

Contact us or raise a Change Request if your site access constraints affect how a cranked beam can be installed.