Pre-engineered Metal Building Column Reactions

[North2South]

I am designing the foundations for a pre-engineered building designed to the 2015 IBC. I want to make sure that the wind load reactions I am designing for are ultimate wind loads and have not been reduced for ASD load load combinations. I don't want to take the 0.6 load reduction on the wind load reactions if it has already been incorporated in the provided reactions. I have tried calling the metal building company and left messages and I have not heard anything. Does anyone have any insight?

 

[jayrod12]

In my experience with PEMBs, they describe the loading in the documentation included with the reactions. Usually on either the page with the baseplates, or the page that precedes the frame loading sheets. It tells you what the negative vs positive values mean, what factors or loading has been used, etc.

 

[Aesur]

I agree with jayrod12, PEMB manufacturers all seem to have their own way of doing it with no industry standard. Their reactions are some of the most confusing things to read through. I am fairly certain they give the confusing individual reactions on purpose to try to take some liability off of themselves by making the EOR figure out the final reactions in load combinations. (I was once told that their insurance companies and lawyers told them to do it this way - obviously unverified and hearsay in my local area.)

 

[phamENG]

Do they just give you an uplift number, or do they specify wind loads, dead loads, live loads, etc.? Usually, it will be unfactored loading (ultimate wind load under 2015 IBC), and you have to add your 0.6 factor to it. Not always, though, so be sure to read it carefully as jayrod and Aesure mentioned.

I have to say, I prefer the load breakouts over controlling reactions. If they used LRFD, you're up a creek for the soil bearing design. If they used ASD, you're up a creek for the anchorage and reinforcing design. That, and if I'm acting as the EOR for the project I want to know for sure that the reactions are correct. Hard to do that without a thorough breakdown of the loads to at least spot check their analysis. Those programs are the epitome of proprietary black boxes, and I'm not inclined to trust them just because the manufacturer does.

 

[Ron247]

Big difference in Preliminary Reactions and actual Final Reactions. Preliminary tend to be fairly conservative from Reputable PEMB companies. Shade and Shelter companies can be anywhere in the spectrum. In the old 1/3 reduction for wind days, I know one Shade and Shelter company that reduced their wind reactions 1/3 right off the bat before they submitted them to the FDtn engineer. Their salespeople told potential Client, "use our building, our foundations are cheaper because we have less uplift."

Not returning my call would REALLY concern me. You need the isolated cases (DL, WL, LL etc) but some tend to send "controlling combination reactions". Controlling for the steel check may not be controlling for the foundations.

Unless you are in a high Snow or high Seismic area, start your foundation design with WL cases. It will tend to govern.