Blocking at end of wood trusses
Blocking at end of wood trusses
(OP)
I'm looking for comments/information on blocking required at end of wood trusses. We generally design our diaphragms as unblocked however we specify 2x blocking at the ends of trusses with a heel height greater than 4". For trusses with a heel height less than 4" we do not require blocking. We justify using the blocking to prevent truss rotation and to help distribute shear.
If diaphragm shear is transfered by truss connectors, is it possible to have a truss heel height of 6" without blocking. If so how do I justify this?
Thx
If diaphragm shear is transfered by truss connectors, is it possible to have a truss heel height of 6" without blocking. If so how do I justify this?
Thx






RE: Blocking at end of wood trusses
RE: Blocking at end of wood trusses
Other than that specific circumstance, I would have to agree with ronstruc.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Blocking at end of wood trusses
RE: Blocking at end of wood trusses
Garth Dreger PE
AZ Phoenix area
RE: Blocking at end of wood trusses
DaveAtkins
RE: Blocking at end of wood trusses
Max spacing of 24" oc.
Max heel height of 6".
RE: Blocking at end of wood trusses
RE: Blocking at end of wood trusses
Garth Dreger PE
AZ Phoenix area
RE: Blocking at end of wood trusses
RE: Blocking at end of wood trusses
A particular contractor (our client) has been complaining about installing the blocking. Before I tell him that we absolutely needed the blocking, I wanted to investigate further.
RE: Blocking at end of wood trusses
If you can't get the truss design(s) to state that a 50 plf shear load at the heel can be transfer to the wall, you can also state that the blocking is only needed in every other, or every third, or etc. bay as need for the shear force.
Garth Dreger PE
AZ Phoenix area
RE: Blocking at end of wood trusses
RE: Blocking at end of wood trusses
Sorry, but I don't put up with that crap. They can pay me now or pay me later their choice, but the blocking WILL be installed.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Blocking at end of wood trusses
This was a perfect case. Our standard was to always specify blocking at the ends of trusses. This particular project was a small, 1-story, box shaped structure with little lateral load. If I can justify reducing the blocking, the contractor will be pleased and maybe we will get some repeat business. If I can't reduce the blocking I'll explain why and the worst case is that the contractor doesn't believe me and goes somewhere else next time.
RE: Blocking at end of wood trusses
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Blocking at end of wood trusses
Garth Dreger PE
AZ Phoenix area
RE: Blocking at end of wood trusses
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Blocking at end of wood trusses
Garth Dreger PE
AZ Phoenix area
RE: Blocking at end of wood trusses
RE: Blocking at end of wood trusses
BA
RE: Blocking at end of wood trusses
Larry
RE: Blocking at end of wood trusses
DaveAtkins
RE: Blocking at end of wood trusses
BA
RE: Blocking at end of wood trusses
Larry
Larry
RE: Blocking at end of wood trusses
Larry
RE: Blocking at end of wood trusses
RE: Blocking at end of wood trusses
Yes, that works well also. Many times, there is a continuous ribbon board out at the tip of the trusses which can get the load into the truss bottom chords.
DaveAtkins
RE: Blocking at end of wood trusses
BA
RE: Blocking at end of wood trusses
my only issue with putting moment into the truss heel or the partial height blocking is that you've still got to collect the linear diaphragm force and dump it into each truss. you're basically taking the edge nailing pattern, which is already tight, and squeezing it even closer.
let's say that you've got 8d @ 6" o.c. as an edge nailing. to put all that into the truss top chord, you've have no nails between trusses and 4-5 nails into the truss. this could probably split the wood all up.
even if you ran some continous metal strapping to catch the edge nailing, you'd still have to attach the strapping to the top chord to transfer 24" of diaphram load.
let's also not forget that the diaphragm and shear wall values for nail spacings are tested values based on a specified assembly. there's some internal effects going on that make the strength of the system stronger than each individual part (the whole is actually greater than the sum of it's parts, they don't correlate to shear values of a single nail).