Pre-engineered Building Reactions

[Cipherer]

Folks:

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.

Thanks!
Cipherer

 

[paddingtongreen]

I have little doubt they should be added but you should certainly ask the EOR for the building.

Do the basic ones include shear? do they add to a net shear?

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[Cipherer]

Paddingtongreen,

Thanks for the response! The Basic Reactions include horizontal and vertical reactions for each column. In some cases, the horizontal bracing reaction is exactly the same as the horizontal basic reaction, which leads me to believe the bracing reactions are already included. In other cases, the bracing reaction is different from the basic reaction; but there are multiple components which make up the total reactions.

Thanks,

Cipherer

 

[RHTPE]

PEMB frames are designed to the exact forces assumed to be applied to them. The interesting thing (from my perspective) is what happens to the internal stresses if the bottoms of the columns are allowed to spread apart a minute amount. The moments in the frame will change and redistribute. PEMB manufacturers tend to assume that the connections to the foundation are exactly correct and do not move.

Yet column base plates may have oversize holes. Anchor bolt locations will undoubtedly vary from the locations expected. Actual as-built conditions will affect the PEMB frame behavior. The horizontal resistance to outward movement of the frame's columns is handled in a variety of ways, yet I have never been convinced of their effectiveness given actual construction techniques.

The disconnect between the design of the PEMB frame and the design of the foundation has always troubled me.


Ralph
Structures Consulting
Northeast USA