Lag Screws into Wood Roof Joists

[JohnnnyBoy]

I have a client that is trying to hang an MUA from an existing 2x10 wood roof joists. Total load is 1000lbs Unf. and will be using a minimum of 18 lag bolts.

I have already calculated the roof joist and they need to be reinforced an additional 2x10 joist at all the connected joists to handle the required load. My issue is the client is looking at supporting the load using a steel SH type channel across approximately 4 joists and lag bolted into the bottom side of the joists.

This scares me for a few different reasons, one being the possible splitting of the wood joists and the second being long-term that the lag screws will give out. I understand that this is what lag screws are meant for although wood does tend to split over the years and soon as the wood splits all withdrawal capacity is lost.

Hoping for any thoughts. I am trying to come up with an alternate connection type for the client but they do want to proceed this way if they can. Any references would also be helpful.

Thanks

 

[jayrod12]

Flat roof or is there an attic?

 

[JohnnnyBoy]

Flat roof, so there is no attic.

 

[jayrod12]

Personally I'd prefer to have blocking installed between joists using framing angles, then thru-bolt the blocking.

 

[JohnnnyBoy]

Jayrod, I am trying to figure out how to make that connection to use through bolts but how would I connect the 3/8" tie rod that is supporting the MUA to the blocking?

 

[jayrod12]

drill a hole through the blocking, push the threaded rod through the blocking, put a washer and nut on the top side.

 

[JohnnnyBoy]

Jayrod,

Very much appreciate the sketch. My only concern here would be bending of the plate although I can easily calculate the bending stress and size it appropriately. Much Thanks

JB

 

[Ron]

Weld vertical tabs on the channel and thru-bolt into the side of joists. Shear connections better than tension connections in wood.