RIDIG DIAPHRAGM CHORD SLIP NEEDED 1

[Cayroo]

I am doing an analysis of a wood-framed rigid diaphragm and I am trying to find the chord anchorage slip of various holdowns and straps. The Simpson Company supplies some but not all of their holdown and strap values. Does anyone know a source for these values? Do you engineering each strap or holdown for slip by the mechanics of the material? Do you use a standard value, say 1/8" or 1/16" for the slip on these holdowns or straps? Thank you.

 

[rlflower]

An engineer's perspective:

I specify Simpson products quite often. Values shown in the catalog should imitate those shown in the ICBO ER report, etc. As far as I understand it, these values are based upon tests done in a lab somewhere using a test jig that complies with standards accepted by the building code.

Slip would depend upon what type of anchor is used. Holdowns with bolts into the wood member would have slippage due to the standard 1/16" oversize of the bolt holes in the wood member. The Simpson PHD holdown uses lag screws which should eliminate this problem. The Simpson PHD also eliminates the other major concern, that of internal distortion of the holdown itself. PHD stands for "pre-deflected holdown."

Slip should be defined as translation of the hardware to the point where the hardware fully engages the fasteners.

Keep in mind that shrinkage of the wood member due to the escape of water content over a long period of time can serve to take up a significant portion of the "slack" in the assembly.