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Torquing thru bolts

Torquing thru bolts

(OP)
Does anyone happen to specify minimum torquing on thru bolts?

RE: Torquing thru bolts

Minimum torque requires that you HAVE to squish the wood - else there is no clamping force. But that depends on the wood species itself, the type of wood (cross-fiber or laminates or impregnated with anti-rot treatment or is well-dry or still wet), and the type of the two beams you clamping.

maximum torque is proportional to all of the same things: If you squisch the two (or three) beams together to tight so the bolt head or bolt and washer or plate is pulled into the wood, the wood is destroyed (visually of course) and structurally. Wood will tend to relax also under years of drying out and continued compression.

RE: Torquing thru bolts

Too much torque will split the members too.

Mike McCann, PE, SE (WA)


RE: Torquing thru bolts

(OP)
I was thinking about specifying a torque that resulted in a clamping force of like 25% of the allowable perp. bearing stresses published in the NDS, using heavy washers.

It is for a pedestrian guard post application, so I don't need a lot of clamping (there is a force-couple resisting the load), but I always worry about the contractor going out of their way to install it like a moron, and I would rather not have a jiggle-y guard system - even if it can handle the ultimate loading.

RE: Torquing thru bolts

Wood members do shrink across the grain with time, so even if you tighten them well, they will likely be loose in a year or so. Maintenance required.

RE: Torquing thru bolts

(OP)
Good point, hokie.

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