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Re: Wood Truss Reinforcement

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I concur with Nels on use of threaded steel tie rods and holddown-like
brackets to the truss. I have done it this general way on several timber
trusses, without however always engaging the heel connection at the ends of
the bottom chord. In contrast to tie rods, long splice plates scabbed across
joints, whether of wood or steel, introduce undesirable, moment-resisting
"arthritis" into joints that need to flex somewhat if the whole truss sags
for any of the many reasons that occur. Split scabs or chords then result.

If your trusses have multiple 2x or 3x members with split ring connectors to
the top chord at the heels, instead of convenient steel side plates, then
the means of connection of the brackets to bottom chord must change. The
bolts in a split-ring connection array are only part of the transfer of load
between members, and would not necessarily be fit to receive all the tie rod
pull.

If there is a space between twin bottom chords, or even if not, the
hold-down brackets can be bolted directly to the bottom chords, the same as
for their use in holding down shear wall boundary studs. In determining
connection specifics, I would use rather cautious, conservative allowables,
and watch out for "secondary" stresses and deformations. In particular I
always design a means of transversely clamping or "stitch bolting" the wood
tension members so that they cannot split apart and release their bolts down
the split, parallel to grain, as I have seen happen. This clamping is
analogous to lateral confinement ties in concrete members. 

If the same (new) bolts pass through brackets on opposite sides of the
truss, care needs to be taken that bolt holes are drilled accurately to the
holes on each bracket. If that accuracy cannot be obtained, then staggering
the hold down brackets lengthwise and using bolts only in single shear is a
possible remedy. 

Charles O. Greenlaw SE