AWC NDS Safety Factors

[DTS419]

What is the basis for safety factors in the AWC NDS provisions for ASD?

 

[ChorasDen]

What is your question, can you be more specific?

 

[DTS419]

What safety factor(s) is provided when designing with the ASD provisions of the NDS?

 

[ChorasDen]

Can you be more specific? What is your question? Your question as it stands is similar to "is this concrete retaining wall safe?". It's too vague a question to be easily addressable.

Are you curious how design properties are established, is that the basis for the question? Are you asking about how load combos combine with properties to establish a level of reliability deemed appropriate? Please provide context.

 

[DTS419]

Specifically, Z values for dowel connectors. What is the safety factor provided when using ASD?

 

[JAE]

I tried to pin down the SF used in the NDS years ago, calling various individuals and organizations, etc. Tough to pin down as the variability of the wood is high and so the actual, statistically "tight" SF wasn't readily available or known. Best I could get was that it landed in the 1.6 to 2.0 range.

This was for wood in general but I would suspect that the SF for dowel action would be similar.

 

[ChorasDen]

JAE is correct, safety factor isn't a term used within the wood industry. We base capacities off a reduced value from the 5th percentile of an assumed standard normal curve, and this adjustment value can range between approximately 1.8 to 2.4, based upon what property is being tested. Keep in mind that this reduction value also incorporates the load duration factor at the design load duration of the test assembly.

AWC has a report called TR-12 which discusses the derivation of their dowel equations, which in turn references the European Yield Mode document hosted by the Forest Products Lab. Might be worth checking those documents for additional context.