Header post reactions of 2nd floor on headers of 1st floor

[Jc67roch]

I guess I have not run into this before, but I am designing a 2 story structure where some of the openings on 2nd floor do not necessary align directly above those on the first floor. So I am winding up with header post (jamb) reactions on the second floor (carrying the roof loads) above (out on the span) of headers on the first floor openings which also carry the wall(s) and floor above. In this case, is it customary to design the first floor opening header to carry this concentrated load out on the span OR just check that the rim joist can carry all the loads at the 2nd floor level over the opening below (acting as a header)? OR lastly, is it just assumed that the rim joist can distribute this concentrated load and the 1st floor header is designed to carry the uniform load of the roof, walls, and second floor over its opening span? A sketch elevation is attached.

 

[jayrod12]

I spec that they block the space below the jamb studs from above and then design the lower lintel for the concentrated load. It usually has the most effect on shear and bearing of the lower lintel.

 

[TehMightyEngineer]

I generally do either #1 or #3; most likely #1 in your case as it's conservative and probably fairly accurate to the load path.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)
American Concrete Industries

https://americanconcrete.com/

 

[StrucDesignPE]

Just curious, are the 1st story walls wood stud walls?

I typically design the headers with a concentrated load from the post above and call for solid blocking at the floor level and a short post down to the header to have a continuous load path.

 

[jdgengineer]

I'd typically design the header for the full load and ignore the rim. However, if there isn't space for the header size, then I would call the rim for the full load and ignore the header. If you design the header for the load, I agree with others you want a squash block to transfer the load from the rim to the header.

I wouldn't normally assume a uniform load transfer to the header below from the rim. I'm not sure the rim would be stiff enough. You could also throw it in RISA or sim with both members in to have a better sense as the load transfer between the two. I wouldn't normally do that, but it wouldn't be a very large time commitment and may give you some better insight.

 

[Jc67roch]

yes, the first floor is studs with a masonry veneer.
Thanks all for the input!

 

[gte447f]

In my experience, customary is definitely to design the lower level headers to support concentrated loads from the upper level jambs above, your 1st option. I would never consider your 2nd option of designing the rim joist as a beam. I have never considered your 3rd option of considering the rim joist as a distribution member to distribute the concentrated loads from the jambs above as a distributed load to the headers below, but that concept may have some merit.