Comparison between CHS and wide flange sections for columns 1

[ingthere]

Which column type would be cheaper to use in mid-height buildings, circular hollow (CHS) or I-Wide flange sections? How would you compare these two types of column sections in terms of economy and efficiency?

To me, circular columns seem capable of doing everything that wide flange sections do, moreover, they provide symmetry. Besides, filling the tube section with concrete provides composite action which increases strength and stiffness. Also, in general they look more "beautiful" to the architects. Downsides are the complex detailing requirements in beam to column connections. However it's not clear to me which one would provide more economic solutions, combining all these factors. Actually the fact that wide flange sections are much more common in practice explains something.. However, still... I would very much appreciate your your opinions..

 

[ishvaaag]

The trees answer your question, in structural terms the round shape suits better loads from unpredictable directions. They also show the need to be firmly rooted, here, joined. We have seen the mast of the dutch TV tower fall this last month under fire, yes, but ... at joint point.

For money matters, all is invention. From the structural viewpoint the flanged items surely are seen more constructible for beings with hands. The torsional creakings in their failure may warn more than the stiff annular sections of impending risk of ruin, that would be then more inadverted; more considering that its very efficient shape in compression when efficiently designed will (or could) be at some concentrated zones closer to limit strength. Just as an example, we have seen at this forum these days the wish to extoll more of an old cast iron column already doing what not was thought for.

 

[ingthere]

Actually, I want to change my way of asking.. Given all the advantages over open sections such as:

a) symmetry in structural behaviour
b) higher compression capacity for the same amount of material used (thanks to symmetry, lower slenderness, and also less residual stresses caused by manufacturing process)
c) Thanks to point 'b', lower seismic mass, less tons of steel used for structure
-possibility to achieve a better composite action with less effort (no extra temporary forwork required thanks to the the closed shape (tube, rectangular..))
-better fire resistance (possiblity to have both internal and external fire resistance. in case of composite columns, only internal resistance can be enough without chaning external dimensions)

howcome these sections aren't much more popular than I sections in the construction industry?

Can't all those advantages cover their only problem "requirement for complex connection detailing and constructability" for the life cycle cost?

 

[vthomidis]

......in my view the main reasons why are two :

- Complex connection detailing as mentioned, which is really
more than just that.CHS are considerably less "flexible" in
designing / detailing / engineering.

- Cost, both in bying the material as in processing it.
( in some cases transport and erection costs are higher also ).

 

[Teguci]

For interior columns, I could see the benefits of pipe columns. The main benefit of Wide flanges is obviously their resistance to bending in one direction. This is key for lateral moment frames. In addition, a moment connection in the direction desired is simpler to fabricate. For corners and outside walls, the framing and connections will point to wide flanges. For interior columns, pipe columns should be fine.

 

[csd72]

It is generally the additional cost of the material and the connections as vthmondis has said.

tube sections are also not as resistant to damage and rust as standard column sections.

 

[ingthere]

So, everybody agrees that the extra cost of constructability of connections is over the cost savings that could be made on the fire protection, material saving, and savings on the formwork in case of composite construction. Thanks for your opinions!

 

[TXStructural]

HSS columns (pipe, round or square tube) are used in the
US almost exclusively in single story buildings, typically with light roofs, like OWBJ. In most cases, HSS sections cost 20-50% more per unit weight, when compared to hot rolled steel column sections. This is the single biggest consideration.

Two other issues are 1) connections to framing members require complicated, welded designs for heavily-loaded beam connections (the connections will usually be more eccentric, also requiring those considerations) and 2) splicing for longer columns. Also, once you reach multiple stories, you have trouble obtaining the required area of steel and adequate buckling resistance and have problems with lateral force-resisting brace connections.

 

[ingthere]

TX,

Could you specify what makes HSS sections cost 20-50 % more than hot rolled steel sections? Is it only due to the manufacturing or is it a life-cycle calculation including the connection difficulties and splicing?

 

[Teguci]

Material alone is a 15% min increase due to fabrication. In addition, HSS shapes are often limited in length due to fabrication (mandrel length and extraction limitations).