Wood wall diaphragm axial load distribution

[SiggiN]

Hi all!

Suppose you have this two storey wall diaphragm:

I am curious about how to distribute the vertical loads (load from roof, snow, wind, floor etc.)and verify that deflections above the windows are small enough.

All studs are spaced 600mm apart (except around windows)

I've marked some areas of interest; S1, S2, S3 and S4

My thoughts/questions:

S1 : Should be straight forward, load is transferred all the way down to the concrete wall.

S2: Can the window header be modeled as a simply supported beam? Where the reaction forces are transfered through the studs to the "edge beam" below as point loads. The studs carrying the extra load will be engeineered individually to verify axial integrity.

S3: To check the deflection of the "edge beam" passing over the window. Should the "edge beam" be modeled as a continious beam with pinned connections at every full stud? With distributed laod from roof, floor, wall and any point load from S2 (reaction forces)?

S4: The "edge beam" will be cantilever at this end. I doubt the dimension shown is sufficient, so might reinforce with steel. Any thoughts in general on postless corner window framing? 2m cantilever might be too much?

- Using some made up numbers, would the free body diagram below be realistic for the "edge beam"? I'm especially curious about your thoughts on the spacing of the pinned connections

All comments/thoguhts are highly appreciated!

Regards
Siggi

 

[phamENG]

A wood stud wall is not designed as a diaphragm as you're suggesting. It works that way as a shear wall for lateral wind loads (if detailed properly), but not for gravity loads. For gravity loads, all of the studs are individual columns (braced by sheathing) and headers are individual beams. If I have to embed my headers within the floor depth as you're implying with your "edge beam" I only thicken it over the opening, and leave the remainder as a typical 1.5" thick dimension lumber or LSL (for engineered wood product floor systems and trusses).

Distribution of the loads is typically done by tributary area to the studs, but that doesn't always work - if you have trusses at 24 and studs at 16, the real picture may be different. There's another thread going right now on that topic, actually.