Design Resources

Frequently Asked Questions

What is the T-stub model and when is it used?

The T-stub model represents a bolt row in the tension zone of an end plate or column flange as an equivalent T-shaped member. The flange of the T represents the end plate (or column flange), the stem represents the beam flange (or stiffener), and the two bolts represent the tension anchors. The T-stub capacity is the minimum of three failure modes: Mode 1 (complete flange yielding, most ductile), Mode 2 (bolt failure with partial flange yielding, most common for UK connections), and Mode 3 (pure bolt failure, avoided in UK practice).

What end plate thickness is standard for UK moment connections?

For M20 bolts, the standard UK end plate thickness is 15-20 mm in S355. For M24 bolts, 20-25 mm. The thickness should be sufficient to ensure Mode 2 governs (not Mode 1), but not so thick that Mode 3 governs (brittle failure). A well-proportioned end plate has t_p approximately 0.8-1.2 times the bolt diametre. SCI P398 provides standardised end plate geometries for UK beam-to-column moment connections.

How are prying forces accounted for in end plate design?

Prying forces are implicitly accounted for in the T-stub model through the Mode 2 formula. The term (2 x M_pl,2,Rd + n x Sigma F_t,Rd) captures the moment equilibrium of the flange, where the bolt tension acts at the bolt line plus the prying force at the flange tip. The prying force is the difference between the total bolt tension and the applied tension. For a well-designed connection, the prying force should not exceed approximately 30% of the bolt design tension resistance.

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.