Vierendeel HSS column design

[JMASE]

Architect wants to have 70ft. atrium columns using HSS sections forming a 4-sided ladder. I can figure the "r" of 4 HSS sections spread apart from each other. The question is, how to figure the spacing of the horizontal ladder pieces to make sure the overall column is not too slender. Ideas?

 

[SWComposites]

If there is any lateral loads on the column, then the “ladder” bars will effectively act like a shear web, so size for the shear loads. For axial loads max spacing could be set by buckling of the individual HSS sections.

 

[TLHS]

At 70ft I'm assuming these are not really part of the lateral system. So minimal lateral stuff with the exception of any p-delta effects.

I would suggest that you shouldn't just design so that your individual elements don't buckle under design loads. You should try to make gross yielding of the overall structure the first failure mode, if reasonable.

The Canadian steel code stuff on built up members does something similar to this. It requires that the individual elements of a built up member be braced together in such a way that the slenderness ratio of each element is less than the slenderness ratio of the overall column. This implies the the buckling strength of the elements will be higher than the buckling strength of the overall shape.

 

[TLHS]

Make sure you've cosidered load distribution into the combined section at the top and bottom as well by really stiffly interconnecting them. Alternately, your overall structure analysis could consider them individual braced columns and account for the actual load distribution.

Realistically, I'd do some hand math on this, but I'd be throwing this into some software regardless and doing at least an approximate P-Delta analysis to make sure I was accounting for the actions of the individual moment frames properly.

 

[dik]

You can calculate the r, roughly based on the four HSS. It will not be conservative; but will be close. The use of all elements requires that there be a stiff 'web shear' component. Early codes had provision for this using C 'lacing' members joining two W sections. A good computer program will resolve this as a check.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Agent666]

This is probably a good example of when you should employ a buckling analysis so you don't miss some global/local buckling modes.

https://engineervsheep.com

 

[JMASE]

Thanks to all for your ideas