NDS Diaphragm Factor, Cdi 1

[tdawgui]

I was going through all the factors that you can apply to allowable lateral design values for single shear connections and noticed the Diaphragm Factor, Cdi. I've never used this factor before and thought I'd take a look into it, but now I'm slightly confused.

Table 10.3.1 on page 58 of the 2005 NDS shows that for a Dowel-type Fastener a Diaphragm Factor can be applied and to refer to Chapter 11 for more info on the Factor. In Chapter 11, the blurb under Diaphragm Factor reads:

"When nails or spikes are used in diaphragm construction, reference lateral design values, Z, shall be multiplied by the diaphragm factor, Cdi = 1.1."

From that, I assume that Table 10.3.1 was incorrectly printed and that this factor is only supposed to be used for nails and spikes (even though Table 10.3.1 shows that it can't be used for nails and spikes)

Am I correct in my assumption? Anyone know the intent behind this Cdi factor? Is it just an allowance for redundancy? Now if my assumption is wrong and it is able to be used for bolts, would a tension chord splice be considered as part of the diaphragm?

 

[JAE]

Table 10.3.1 refers to Lateral Loads on the upper portion of the table (where it says "Dowel-type Fasteners". Dowel-type Fasteners include nails and spikes.

The lower portion of the table lists most of the dowel-type fasteners separately under the Withrawal section.

So Cdi does apply to lateral loads on dowel-type fasteners that include nails.

So I see no conflict.

 

[KBVT]

Not applicable to tension chord splice. See the Breyer text, he has a pretty good explanation on the adjustment factor. It is not used very often because the diaphragm capacity tables in the IBC are based on testing and most pull capacity values directly of the charts, usually not a need to manually calculate diaphragm capacity based on individual fastener capacity.

 

[tdawgui]

Thank you! I looked at the Breyer text and it seems pretty straightforward now.