AD 550: Stiffness classification forwelded beam to column joints

If a bolted beam to column joint is to be classified as “rigid”, practical recommendations are contained in the Green Book on moment-resisting joints (P398). To be classified as rigid, the critical mode for the top row of bolts is to be Mode 3 (bolt resistance is critical rather than modes involving flexure of the plate) and the column web panel shear force must not exceed 80% of the design shear resistance.

This AD provides complementary advice for welded beam to column connections, which in due course will appear in a revised version of the Green Book.

For a welded beam to column connection to be classified as rigid without recourse to calculations or analysis by software, the joint should meet the following requirements:

• Stiffeners, of equal (or greater) width and thickness as the beam flange, should be provided across the full width of the column web.
• The beam to column flange welds should be of equal strength to the beam flange, and the welds between the stiffeners and the column flange should have an equivalent resistance to the beam flange welds.
• The column web panel shear force must not exceed 80% of the design shear resistance.

Alternatively, by using limited calculations, the following approach may be adopted:

• The detail should satisfy the requirements for welding to unstiffened flanges, or stiffeners aligned with the beam flanges should be provided in the web of the column. Although rules for welding to unstiffened flanges are provided in BS EN 1993-1-8, the UK Connections Group recommend that the requirements given in clause 6.7.5 of BS 5950 be adopted.
• When stiffeners are required, they should be of equal (or greater) width and thickness as the beam flange, unless smaller stiffeners are proven by calculation.
• The welds to the beam flange should be designed for the applied loads applied over the effective width of the flange, or may be sized to be of equal strength to the beam flange.
• The welds between stiffeners and the column flange should have an equivalent resistance to the beam flange welds.
• The column web panel shear force must not exceed 80% of the design shear resistance.

Contact: David Brown
Tel: 01344 636555
Email: advisory@steel-sci.com