discontinuous chords in wood framed building

huangyhg

discontinuous chords in wood framed building
i have a situation where the exterior walls between shear walls step multiple times, making the double top plate chords discontinuous.(see diagram below x=shear wall)
the floor framing runs parallel to the shear walls. i was thinking of considering the depth of the diaphragm to be the distance between the innermost exterior wall segments.  then adding blocking & straps between the floor trusses along these lines to create continuous chords.  any comments, suggestions?? is there a better way?
thanks,
ice
x------
x      ------
x            ------x
x                   x
x                   x
x                   x
x                   x
x      ------       x
x------      ------x
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i think you are approaching this correctly.  if your chord force is low, you may want to consider using some floor sheathing as a chord, instead of putting in all the straps and blocking.
daveatkins
straps and blocking is the right approach.
i'm not sure how you would design the system using some of the floor sheathing as a chord.
i've only ever seen it done once, but i agree with daveatkins;  it is possible to use the floor sheathing, but not recommended practice.  the design was based on the sheathing acting as the top portion of a t-beam...  not something i would do personally in one of my designs.
b.eng (carleton)
working in new zealand, thinking of my snow covered home...
i think the code frowns upon (or forbids) doing this, but you take a width of osb, 4' for example, and figure out the chord capacity by looking at the nails available where the end of one sheet of osb meets the next.
daveatkins
the 2001 cbc (1997 ubc) prohibits the use of sheathing to transfer tension at diaphragm openings (2315.5.2), but allows the use of sheathing to splice collector/chord elements at diaphragm boundaries (2315.5.3).
if i understand the original post correctly, the floor framing at the top of the shearwalls is in line with the offset shearwalls. if this is accurate, consider using solid framing members instead of trusses at the collector lines and either (1) making them continuous between the exterior walls, continuing for the full length of the shearwalls, or (2) running the solid members to the interior ends of the shearwalls and using straps to tie them to the shearwall top plates. this way you end up with only one strap at each collector line, or none if you can go with a full length member.
if you do go with lines of blocks and strap to create collectors, follow up and insist on structural observation: it has been my experience that builders will ignore it and building dept inspectors won’t notice that it wasn’t built.
-nkt