October 19, 2018

Eurocode C1 Factor for Lateral Torsional Buckling

Eurocode lateral torsional buckling capacity is calculated per equations in Annex F in the ENV 1993-1-1:1992. This calculation uses variables C1, C2 and C3. Since there is no generic formula in the Eurocode to calculate the moment gradient factor, C1, RISA will use the widely accepted López, Yong and Serna method by default.

The method proposed by López, Yong and Serna in their paper “ Lateral-Torsional Buckling of Steel Beams: A General Expression for the Moment Gradient Factor” to determine the moment gradient factor takes into account both the moment diagram and support conditions. The general proposed closed form expression presented by López et al is the following:


Where k is,


A1 and A2 are given by,




The contribution of the support conditions are considered in the k1 and k2 terms. When lateral bending and warping are free, k1 or k2 is equal to 1.0 for the corresponding support. When lateral bending and warping are prevented, k1 or k2 is taken as 0.5.

The values rendered using this closed form expression have been shown to match closely with numerical results in comparison to methods proposed by AISC and BS 5950-1. However, the user can always override this value within the Design Properties in the Properties Panel.


Alternatively, this override is also in the Hot Rolled tab of the Members spreadsheet.

C1 2

Tags: RISA-3D RISAFloor Eurocode Steel

You may also be interested in

Nov 8, 2018 | Tips & Tricks
Mat Slab Overturning and Sliding Safety Factors

RISAFoundation v11.0 includes two new tabs in the Safety Factors resul...
Read More

Aug 21, 2019 | Tips & Tricks
RISA-3D v18 Sneak Peek Videos

The new release of RISA-3D is right around the corner! Check out our t...
Read More

Jul 12, 2019 | Tips & Tricks
Implementing Realistic Behavior for T/C Members in RISA-3D

Tension or Compression (T/C) Only members are commonly used in steel b...
Read More

Jun 20, 2019 | Tips & Tricks
Understanding Wall Panel Forces with Rigid Diaphragms

Rigid diaphragms represent a plane of very high rigidity and distribut...
Read More