SDS screws edge and end distances

[AaronMcD]

Just wondering if it is ever acceptable to relax on the ICC report's very large end distance - 4" in all load directions for a 1/4" SDS screw vs NDS 4D to 7D for "dowel type fasteners".

I ask because it seems common for engineers and contractors to use structural wood screws all over the place with little regard for ICC end/edge distances. Specifically I am reviewing a calc from a wood-specialist engineer providing some of the timber connection details on a project we are doing and he doesn't seem to pay attention to ICC reported end distances. Is there a reason the ICC reports don't use NDS equations?

Thanks,

Aaron

 

[Triangled]

can't say I've reviewed the ICC report on this closely.... can you pls upload it?

 

[AaronMcD]

I just search online whenever I'm looking for an ICC report. Here is the link:

http://www.icc-es.org/reports/pdf_files/esr-2236.pdf

 

[NorthCivil]

Steel and concrete aside, my experience is that fastener design aides are immature (especially small fasteners with tight edge distances)

in cases where you need to apply fasteners to situations that dont fall within published, well defined, clear cut design guides, use your engineering judgement.

 

[Ron]

It's called "engineering judgment". Yes, the engineer's liability is increased if the published reports are not followed; however, those reports are often very conservative.

 

[wannabeSE]

I'd ask Simpson. Alternatively, ask the engineer designing the connections to verify screw capacity with the reduced end distances. Also, the SDS screws have a drill point and do not require predrilling wood. Maybe, the wood splits easier with an SDS versus a traditional screw with lead and clearance holes.

 

[Triangled]

looks like not 'all directions' for 4", but granted the SDS screws have greater specified distances than NDS. But the SDS screws also have bigger allowables that the NDS, and that extra bang isn't gonna come for free.

Based upon glance at ESR provided and NDS footnotes, it appears that the SDS steel quality is substantially elevated above the NDS. If that is the case, (I hope someone checks me) I can imagine that several of those 6 yield equations have been rendered moot such that now, with the SDS screw, the wood itself governs. Hence bigger distances for bigger allowables.

Does the manufacturer have some comfort factor in those end/edge/space distances? I am sure they do, and also that their analysis equations did not come out as exactly 4.00000 inches.

Would I use different edge/end/space distances than the ESR report? Almost for sure not, unless I ran the 6 limit equations in the NDS.

Thanks for bringing this item to the forum as I had not noticed it before.

 

[msquared48]

The last comment in note 9 in the 2017-2018 catalog says " For smaller spacing, please contact Simpson Strong-Tie Engineering."

As wannabeSE said, start there...

Mike McCann, PE, SE (WA)

 

[msquared48]

Just for the heck of it, I called Simpson, as we use SDS screws a lot too.

From what I heard, I understand that:

1. Simpson's values and distances are conservative compared to the NDS. They are for untested applications. Their primary focus on the larger distances is to avoid splitting of the wood.

2. Other Simpson connectors in the catalog use SDS screws with smaller distances, but they are rated and tested applications.

3. If you want to use distances smaller than the Simpson values, revert to calculating the values using the NDS Tables and the appropriate reduction factors.

Seemed to be a reasonable approach to me...





Mike McCann, PE, SE (WA)

 

[Triangled]

so MSquared48, am I understanding you right?

If you want to use Simpson values, use Simpson dimensions (and applications).

If you want to use NDS dimensions, use NDS values?

 

[msquared48]

That's the way I understood what their engineer said.

I am going to call again though, as it seems to me that the NDS factors would still need to be applied to the Simpson values.

I will post back later.

Mike McCann, PE, SE (WA)