COLUMNS - WIDE FLANGE OR HSS? 1

[jpw2913]

I am wondering if I could get some input from the community about how you determine whether to use a wide flange column or an HSS column.
We are currently looking at a 3 story building that will have some moment frames for the MWFRS. The architect likes the use of HSS columns.
In situations where we need a moment connection in each direction on a corner column, they are nice (square HSS). But I'm just curious how some
of you decide when to use HSS vs. WF. Thanks for any input!

 

[mike20793]

Are they wrapped architecturally at all? If they want exposed columns, then HSS are easier on the eyes. If they are wrapped I would go with wide flange columns. You will get better results for drift, they are cheaper, and they are more economical from a weight per foot standpoint (for equivalent moment of inertia, drift related). For one story buildings, I use HSS columns quite frequently, but I haven't on anything more than one story. I also try to avoid biaxial bending on my baseplates because they can get quite large from the orthogonal wind combinations. It's usually not an issue for one story, but it may be for 3. Of course, that point is moot if you use pinned bases in your moment frames.

 

[BUGGAR]

I try to stick with structures where the Engineer decides this. I generally go with WF unless torsion dictates otherwise. Box girders can be good, too.

 

[SAIL3]

WF..better moment capacity, better drift characteristics
HSS..better axial load capacity, better torsional capacity, however, connections can be a PITA

 

[msquared48]

With moment frames, use Wide Flange sections considering the connections.

Mike McCann, PE, SE (WA)

 

[jpw2913]

Thanks for the replys. I've always struggled with this in the cases where we need moment frames in each direction. A WF is great for a moment frame in the strong axis of the column, but what about when you need lateral resistance in the other direction (weak axis of the WF column)? A moment connection into the web of a WF is not typically done, is it?

 

[mike20793]

You just provide a moment frame with the column strong axis in the other direction.

 

[JAE]

And HSS column-beam pre-qualified moment connections haven't been developed/approved yet if you are in a high seismic area.



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[KootK]

1) Last I checked, the cost of ordering the material was quite close and fluctuated such that it was almost a dead heat.

2) For gravity columns two stories or less, I like HSS. They're clean architecturally and, as long as you can use a single two story member, connections come cheap. Just knife plate connections everywhere. It's tough for small wide flange's to compete with small HSS sometimes because the weak axis beam connections require beam flange coping. For buildings tall enough to preclude full height HSS columns, spice connection start to add cost. There really isn't a great HSS bolted splice connection that doesn't eat up floor space.

3) For moment connections, it's strong axis wide flange all the way. HSS moment connections tend to be inefficient and costly. This is particularly the case if you need to develop some of the side wall strength in flexure which is a real possibility given the nature of the cross section. Interestingly, in Japan, HSS moment frames are a popular choice. They've produced a ton of good design information on the connections.

4) If at all possible, plan your structure to avoid weak axis wide flange moment connections. It's a bear evaluating non-orthogonal load cases and, to my knowledge, there are still no prequalified seismic moment connections for wide flange / weak axis frames. That said, weak axis moment connections are done all the time. You wouldn't be blazing a new trail. Sometimes a building corner's just a real convenient place to drop a pair of adjacent, orthogonal frames.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[wannabeSE]

JAE,

If you don't mind concrete filled HSS16x16 columns with proprietary forged collars at the connections, ConXtech's ConXL moment connections are prequalified in AISC 358-10.

http://www.conxtech.com/

 

[JAE]

wannabeSE - yes I forgot to mention that there ARE proprietary connections for tube columns that are prequalified (SidePlate is one too).
Good point!



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[Leftwow]

AISC Steel Design Guide 24 is Hollow Structural Section Connections.

 

[JAE]

DG 24 doesn't include seismic moment connections though. Having said that, the OP didn't indicate where their building was located or if seismic was an issue.




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[jpw2913]

Thanks to all for the input...much appreciated. The building is located in Texas in a low seismic zone. Wind will control the lateral load resisting system.