Perpendicular bearing on top and bottom wood plates

[mrengineer]

I am designing a 4 story wood building (26' long wood trusses on both sides of 6' wide corridor). The trusses will be bottom bearing at the corridor walls-not sure yet if I will use dimension lumber or trusses over the corridor. The axial load on the bottom story results in perpendicular to grain bearing stress from 2x6 studs on the top and bottom plates of about 800 p.s.i., which is roughly double the allowables for S-P-F or Hem-Fir commonly used in this area. I could go with Doug-Fir, which will increase the allow perpendicular to grain bearing stess to 625 p.s.i. and call it good. I wonder though if I am worrying about something that is commonly not considered. This is somewhat like the discussion some time age concerning the ability of the double top plates to span between studs when there is a load applied between the studs. I have a gun to my head concerning costs on this project (as usual), and don't want to be any more anal than absolutely necessary. Any thioughts would be greatly appreciated.

 

[jheidt2543]

One thing to think about with a 4 story wood frame structure is the possiblilty of wood shinkage. I have seen 2" of shinkage over a 1-1/2 to 2 year period which played havoc with sliding glass patio doors on the 4th floor level at the outside walls.

 

[EIT2]

I cannot help with answering your question, but, I am interested in the answer to the double top plates with the load applied between studs, such as 24 oc roof trusses over 16 oc studs.

Would you care to elaborate on that while waiting for your answer?

Thank You

 

[mrengineer]

EIT2
See the thread "Wood top plate capacity" There was considerable discussion on this topic.

 

[Trussdoc]

Section 2.3.10 of the 1997 NDS allows an increase in the bearing strength when the load is at a distance from the end of the bearing plate. The increase in value is stromgly dependent on the width of the load. For an 1 1/2 inch wide stud, it is 25%.