General Effects of Lateral Load on Steel Member

[IlliniPE]

This is a very general, possibly hypothetical, question, but I was wondering if anyone has come across any literature that gives a rough estimate for the increase in steel size for lateral loading vs only vertical loading. I ask because I have a client that wants to know a rough comparison of steel needed for two separate vertical loading conditions. For these preliminary discussions, would it be fair to say lateral loading will result in an XX% increase in steel size? That is, the columns need to be W12x30 considering vertical only, but an increase of 30% in strength would be in the ballpark for lateral loading, too. I know there are many factors that determine those lateral loads, but I was wondering if an upper limit, conservative number had ever been determined. Would it even be possible to do so for quick, schematic purposes?

 

[KootK]

I'm going to assume that you mean to compare two cases:

1) Columns and beams for gravity loading only.

2) Columns and beam used for gravity loading and for lateral loading (wind/earthquake), in the form of moment frames.

If that's accurate, I doubt that you'll find a meaningful rule of thumb. That, because most buildings nowadays concentrate building lateral resistance locally. So a given frame might take only 1/20th of the gravity load applied to the building but wind up taking 1/2 of the lateral load applied to the same building.

Your odds might be better if you were looking at a building where all of the gravity columns were also moment frame columns, as has been done in some retail buildings historically.

 

[IlliniPE]

2) Columns and beam used for gravity loading and for lateral loading (wind/earthquake), in the form of moment frames.

Yes, for moment frame applications. Forgive me, it has been quite the Monday. This is for a nonbuilding structure that will consist entirely of moment frames. I realize now just how vague and general my question was. But yes, just searching for any sort of rule of thumb, mostly just for conversation sake.

 

[KootK]

This is for a nonbuilding structure that will consist entirely of moment frames.

I'll be interested to see what others come up with but, even with that simplification, I'm at a loss. Consider:

1) Heavier buildings will suffer from P-Delta effects more greatly.

2) A rule of thumb for weight, if it exists, will likely be eclipsed by the need to consider the cost of the different manner of beam/column connections between moment frames and gravity frames. Most of the cost may wind up in the connections. This might actually be a viable path forward if you consult with a fabricator on the relative cost difference between moment frame connections and gravity frame connections.

Your initial instinct might be right: it needs to be a literature thing. Maybe some one has done a parameter study or something in the past.

The only relevant experience I have is in looking at those retail buildings that I mentioned earlier. One story malls where every column is part of a moment frame. In those situations, I feel as though maybe a 50% increase in weight would be in the ballpark.

How many stories is your structure and what is its function?

 

[jerseyshore]

Way too many variables IMO. I agree with KootK that the connection costs with MF's can easily dwarf just upsizing the steel sizes. I think asking a fabricator who does a lot of steel building type structures would be your best bet.