how? find compressive resistance of single unbraced angle 2

[knownot]

According to CSA S16.1-M94; Axial compressive resistance is:
Cr=phi x A x Fy x (1 + lambda^2n)^(-1/n); (section 13.3.1)
- appendix D suggests how to determine lambda
- however, n is specified only for W,I, Box,HSS, and WWF members and no guidance is given regarding L-members.
- Specifically, I am interested in suitablity (Canadian Code) of L127x127x13mm that is 3.55m long with pinned ends, for carrying load of 24kN in compression; actually, load is reversible depending on wind direction to Tension of 29kN.
Thanks

 

[Ron]

The tension load is not a big deal. In compression, your actual compressive stress is also relatively low. You need to be concerned about the slenderness of the member in compression, to prevent buckling. Check Kl/r. If under 200 (assuming primary loaded member) should be okay. If over 200, provide secondary bracing to cut the unbraced length (l). Though I'm not familiar with the Canadian code, it looks as if the equation is considering the slenderness.

 

[knownot]

Ron- you're right; lambda is a function of kL/r, which is about 90 in this case, and I have a level of "comfort" about the member selection, since the stress (P/A) is relatively low. However, I prefer to quantify the strength at onset of buckling, and there does not appear to be explicit guidance on selection of the 'n' value, which is intended to correlate somehow with the type of steel shape used.

 

[panos]

The Canadian Journal of Civil Engineering vol 23 , 1996 p.632-638 has a very helpful discussion on how to calculate the axial capacity (compression) of a single angle.
Title of article : "Design of single-angle compression members according to the Canadian Standards"

Check your local engineering library or e-mail me peter@naeng.com and I will fax this to you.


Thanks
Panos, P.Eng.

 

[knownot]

Panos thankyou very much.

 

[JAE]

You probably already know this but make sure that the "r" you're using is rz and not rx or ry. For a free angle, it will first buckle about the z axis.