Design Resources

Frequently Asked Questions

What is the standard UK detail for a CHS brace connection?

The slotted gusset plate connection is the standard UK detail for CHS bracing. The gusset plate (typically 12-20 mm thick in S355) is shop-welded to the beam-column joint, and the CHS brace is longitudinally slotted to accept the plate. Fillet welds on both sides of the gusset within the slot transfer the brace force. The slot width is the gusset plate thickness plus 0.5 mm fabrication tolerance. This detail is standardised in SCI P358.

How is the weld length determined for a slotted CHS brace connection?

The required fillet weld length per side L_w = N_Ed / (2 x Fw,Rd), where Fw,Rd is the design fillet weld resistance per unit length per EN 1993-1-8 Clause 4.5.3. For a 6 mm fillet in S355: Fw,Rd = a x fu / (sqrt(3) x beta_w x gamma_M2) = 4.2 x 470 / (1.732 x 0.85 x 1.25) = 1.07 kN/mm. The slot length = L_w + 2 x return weld allowance (2a each end). For a 450 kN brace: L_w = 450/(2 x 1.07) = 211 mm, slot length = approximately 220 mm.

Does the UK NA modify the brace connection design rules in EN 1993-1-8?

The UK NA to BS EN 1993-1-8 does not modify the brace connection design rules. The standard provisions for welds (Clause 4.5), bolts (Clause 3.6), and block shear (Clause 3.10.2) apply without amendment. The UK NA confirms gamma_M2 = 1.25 and references SCI P358 for standardised UK bracing connection details. The UK NA also references BS EN 1090-2 for the execution requirements specific to brace connections, including permissible slot straightness tolerances and weld access requirements.

When is a gusset plate stiffener required for a compression brace?

A gusset plate stiffener is required when the gusset plate free edge length (from the last bolt to the Whitmore section tip) exceeds approximately 8 times the gusset plate thickness. For a 12 mm gusset, this equates to a free edge of 96 mm. The stiffener prevents local buckling of the gusset plate under compression. In UK practice, stiffeners are typically provided as triangular plates welded perpendicular to the gusset, or the gusset thickness is increased to eliminate the need for stiffening. SCI P358 provides specific geometry limits.

Educational reference only. All design values are per BS EN 1993-1-8:2005 + UK National Annex and BS EN 10025-2:2019. Verify all values against the current editions of the standards and the applicable National Annex for your project jurisdiction. Designs must be independently verified by a Chartered Structural Engineer registered with the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE). Results are PRELIMINARY -- NOT FOR CONSTRUCTION without independent professional verification.