Metal Building / Pre-engineered Building Reactions

[Xam-Struc-Eng]

Hello All,

Please see the following question, I am copying this from another thread (posted by Ciphere) where it was not answered. I have the same question and trying to find an answer.

"I am designing foundations for a PEMB designed with MBS software (Dr. Dean Jorgenson, et al). The MBS reactions data contains a table entitled "RIDGID FRAME: Basic Column Reactions" and another table entitled "ENDWALL COLUMN: Basic Column Reactions". A (small) separate table is entitled "Building Bracing Reactions". I am trying to determine if the bracing reactions are already included in the Basic Column Reactions, or if they should be added to the Basic Column Reactions to determine the loads imposed on the foundations. I would appreciate any insight / experience in this matter."

-Xam

 

[JedClampett]

Short answer: Probably not.
Longer answer: When not sure either ask the PEMB Designer (good luck) or just combine them in the most conservative way.

 

[thaidavid40]

My experience with these PEMB suppliers has universally been that the basic reactions DO NOT include the bracing reactions, and those must be added (or subtracted) from the proper reactions by column location. But, as JedClampett says, it never hurts to pick up the phone and find out for sure.
Dave

Thaidavid

 

[jimstructures]

My experience agrees with the earlier posters, Butler is the only manufacturer that I know of that includes bracing with frame reactions and that only applies to X-rod bracing, not portal frame bracing, windposts, portal braced frames, etc. Butler will have a note in their reactions that X-rods reactions are included. If the other manufacturers don't say the bracing reactions are included, then it should be safe to assume they are not included. I also agree a phone call is the safest way to sleep well at night.

Jim

 

[JedClampett]

As a tip, it's very possible that the engineer who sealed the calculations and drawings might not be the one who did the calculations. This might account for the defensiveness I sense when I ask them questions. If you could track down the actual "hands on" engineer, you might have more luck.
It makes logical sense that the bracing loads (likely coming from wind or seismic in one direction) and the portal uplift (coming from wind or seismic in the perpendicular direction) shouldn't need to be combined. But there's diagonal cases, direct uplift (on the roof) among others, so without any guidance I'd add them together.

 

[Xam-Struc-Eng]

All,

Thanks for your valuable suggestions. I did call the building manufacturer and talked to them. Turns out that they included the Bracing Reactions in the Basic Column Reactions table, and they suggested to use bracing reactions as Zero "0". The bracing provided in this case is X-Bracing.

There are multiple wind loads (WIND_LEFT1, WIND_RIGHT1, WIND_LEFT2......) given in this table, and I am trying to use Factored Load combinations (1.4D + .....) from ASCE 7-10. Can anyone provide some input or share their load combinations so that I can learn the acceptable design method? I am trying to accommodate only one wind load in a combination but not using multiple wind loads in a combination. Generally, do anyone use two or more wind loads adding into one combination? My foundation is a Shallow Foundation with a grade beam tying into it. Please let me know if this question is not clear to anyone.

Thanks!

 

[darthsoilsguy2]

this is a good book. there is probably an example problem with discussion on each step, including the load combos.
Foundation and Anchor Design Guide for Metal Building Systems 1st Edition - Alexander Newman