Compression members governing equation

[JoeH78]

HI all,

I'd like to know when we are determining that the H1-1 and H1-2 shall be used as governing equation in AISC-ASD Combined Stresses section, since there is no any provision for that in AISC-ASD. Most possibly we should calculate both of them and whichever is smaller that is the governing equation, right?

Additionally, related with compression members calculation, which is the most effective way of calculating the effective length factor (K) for steel or RC structures (preferably in equation/computerized manner)?
Googling reveals numerous way of determining it, e.g in British Standarts (5950:2000) gives 0.5 + 0.14*(k1+k2)+0.055*(k1 + k2) (non sway structures), there are also Duan–King–Chen Equations, Newmark Donnell and French equations, but which one is most effective and gives accurate results? I really wonder how nowadays softwares calculates the effective length factor e.g. Sap2000, StaadPro, if someone can shed some light into that issue I'll appreciate it?

Regards,

 

[JStephen]

I don't understand a good bit of the question.

I believe the member has to satisfy both the H1-1 and the H1-2 equation, not the lesser of the two, per the provisions for that in AISC-ASD.

I assume you are referring to the K factor in two different planes for the same member? But in that case, I can't think why you'd need to combine them.

 

[JoeH78]

>I believe the member has to satisfy both the H1-1 and the H1-2 equation, not the lesser of the two, per the provisions for that in AISC-ASD.
I think so, I completely mis-treated it.

I'm not trying to combine them, I'll calculate the K factor for both principal axes of member. There are numerous ways to do it using alingment charts and formulation manner(which I prefer). AFAIU these ways give the different results(K factors) depending on the shape of structure. Regarding the steel structures which one is most effective way ?

One more thing comes in mind, how the K factor is calculated for a column in a frame if it has obliquely connected girders(connection problem is another issue), how much of their slendernes(girder members) will contribute to the distrubution ratio to Ga and Gb and how ? Can I simply assume the slenderness will be distributed with connection angle ?

Hope that it's clear enough,

 

[JoshPlumSE]

Just to clarify, I assume that we're talking about AISC - ASD 9th edition....not the AISC-13th edition ASD.

The treatment of K factors will be significantly different between those two codes. The newer code (13th edition) will normally allow a K value equal to 1.0 provided that your analysis meets certain restrictions. The older code (9th edition) generally uses idealized assumptions or alignment charts.... see the commentary on Chapter C.