Odd Wood Connection

[SteelPE]

I have a project where I need to hang a mechanical unit from the underside of a 4x wood member with a threaded rod. I would like the load to be concentric on the existing wood member to avoid adding blocking to the existing members. I am having a hard time finding a connection that can load my existing member concentrically without making something up out of steel (quite costly).

A colleague of my suggested I use a Simpson post base to connection my hanger rod to my existing 4x wood member (something like an ABU46Z). The capacity of the connection only needs to be for 300 lbs/location.... a ABU46Z has an uplift capacity of 1,850 lbs (which has been increased for wind and earthquake loadings).... so my capacity under this condition would be approximately 1850/1.6 = 1,150 lbs.... which is much greater than the demand of 300 lbs.

Has anyone used this type of configuration in the past? I don't see why it wouldn't work..... but it is an odd use for this type of connector.

 

[jayrod12]

I don't mind this idea. Another alternative would be two DTT2Z connectors, one on each side of the 4x, with a piece of unistrut bolted to them. Would result in a concentric loading, would get the wood fasteners up above the neutral axis, should have substantial capacity and would leave the mechanical contractor with something to connect to that they're very familiar with in the uni-strut.

 

[milkshakelake]

You can hang down two unistruts and put a theaded bolt or another unistrut to bridge the gap. Or just use wood 2x4 for all of this, with lag screws. Use plate washer on your hanging threaded rod; even though 300 lb isn't much, I'd rather have a bit more bearing. I'd design the lag screws for extra capacity in the hanging condition, like how anchor bolts use higher safety factors and increased inspections in overhead installations.

 

[KootK]

I don't see why it wouldn't work.....

Depending on the depth of the supporting member, one might argue that it violates the "rule" about delivering cross grain load to members at their centroid or higher. I violate that all the time but that's another conversation.

 

[Craig_H]

I'd also be open to a couple of structural screws or even lags loaded in withdrawal, holding a unistrut to the underside of the joist. It would be nice and minimalist. You won't need a ton of thread engagement to get 300 lbs of tension resistance, but it wouldn't be onerous to use long enough screws to get the load applied above the neutral axis.