STAAD.Pro doesn't work out the slenderness of double angles to Eurocode 3, and instead suggested to use BS5950.
Does this mean for STAAD to design double angle members, it will be designed to BS5950, while the rest of the sections to Eurocode 3?
EC3 does not specify explicitly how to work out the slenderness of double angles. So what we currently do is to use the slenderness clauses from BS5950 to work this out. For double angles, we use Cl.4.7.10.3 of BS 5950. You can use the LEG parameter to specify the various cases given in Table 25 of BS 5950.
Thanks for the reply. I've attached my model below.
I assigned double angles to the top and bottom chord of one frame first.
I have also used the LEG parameter as you mentioned, but it still returns a warning that it has aborted design to Eurocode for the double angle.
Or is there any parameters/command that is missing to proceed with the member design of the double angle to Eurocode?
Tengah ESS Roof Truss v0.STD
The double angles in your model are classified as 4th class sections (slender) and the design of slender double angles is not supported by the EN 1993-1-1:2005 in STAAD.Pro.
Does this mean if I assign a smaller section, it becomes more slender, right?
However, I tried assigning smaller double angles and it becomes class 3 (non-compact)? and design results are showing, although the section is still failing.
I hope you could clarify.
The smaller section will be less slender. STAAD will design a 1st, 2nd or 3rd class double angles, but not 4th class. If the unity ratio is above 1, then the forces acting on the member are too high and the section is failing the code check.
Answer Verified By: Joaquin Ong
I am in a dilemma here. If I assign a larger double angle, STAAD will classify it as 4th class, and design is unsupported. If I assign a smaller double angle, it will be classified as 3rd class, and section will fail because it can't carry the forces.
Do you have any suggestion on how to proceed, if I want to assign double angles to the top and bottom chords?
You may try to use a thicker sections, i.e. UA120x120x12. This should not be a 4th class section, but would have higher dimensions, so could resist higher loads.
I met the same situations in recently. The member can pass in a single angle UA150x150x10, but 2 UA100x100x10. I realized that staad give me wrong slenderness ratio in y-axis. See photo below. Please be advised.
For double angles, STAAD uses Cl.4.7.10.3 of BS 5950 to calculate slenderness. You can use the LEG parameter to specify the various cases given in Table 25 of BS 5950.