Wood Connection Question 1

[jwags]

I currently have a wood plate attached to the top of a concrete wall supportin wood roof trusses. The trusses were built with a heel height that was 4.5" too short. Our solution is raise the trusses and bolt (3) more 2x plates to the existing one. When you analyze this connection using NDS can you consider your main member 4.5" thick and your side member 1.5" thick? Do the yield limit equations still hold for multiple plies that are unconnected? How should the connection be designed? I need to transfer about 400plf of shear load out of the roof diaphragm. Any help would be great.

 

[msquared48]

Anchor bolt the bottom plate to the wall, sequentially nominally nail the other three plates omn top, and nail Simpson A35's or equal to the sides of the plates as needed to transfer the load from plate to plate. Between the nominal nailing and the A35's, the 400 plf should be no problem.


Mike McCann
MMC Engineering

 

[jwags]

msquared48 - Thanks for the advice.

The one that I would really like to know is whether or not the NDS equations are still valid for unconnected plies connected together at certain intervals. For my case I guess what does it take for the NDS equations to be valid for attaching (3) 2x8s flat to a single or double plate that is already installed on top of the wall with anchor bolts.

 

[TTUengr51]

In my opinion, if the plies are not adequately fastened to create a composite member to resist the shear force, then you should consider the 1.5" thickness and not 4.5".

I agree with msquared48, use nails and A35 clips to transfer the shear force. Two (2) 10d common nails spaced at 12" o.c. would give a little over 400 plf capacity using a duration factor of 1.6.

Another consideration...with the increased sill plate height, what measures are being taken to transfer any uplift forces from the truss into the concrete wall?



Nick Deal, P.E.
Michael Brady Inc.

http://www.michaelbradyinc.com

 

[H57]

The concern that I would have is lateral load transfer from the wall to the roof diaphragm. Typically the roof diaphragm is used to take out loading perpendicular to the wall (wind/seismic). If you add additional plates is the anchorage to the wall adequate to resist rotation/uplift at the joint?

 

[ron9876]

A better option may be to require the truss supplier to provide a detail to increase the depth of the truss bearing.

 

[BAretired]

Just out of curiosity, what is NDS?

BA

 

[Splitrings]

NDS (National Design Specification) 2005 section 11.3.8 states that shear connections with 4 or more members must be analyzed as a series of single shear connections. I would interupt this to be a 1 1/2" side and a 1 1/2" main member. Figure 11D apperas to apply to your case.

 

[BAretired]

Whether the shear is applied parallel or perpendicular to the wall, it has to be resisted at every face, so the extra three top plates have to be considered as individual members.

If the shear is applied perpendicular to the wall, you must also consider the overturning of the stack of plates. At the top of concrete, the moment will be 400# * 6" = 2400"# per foot of length.

I tend to agree with the suggestion that it would be better to modify the wood trusses to provide the required heel height.

BA