Wood Load Duration Handrails 3

[bob96]

For the 200 pound concentrated and 50 plf handrail/guardrail loads in the IBC, when designing wood members what is the NDS load duration that should be used? Ten minute = 1.6? Is there a NDS or IBC code statement that specifies the load duration?
Thank you

 

[JAE]

Since the IBC defines this as a "Live Load" in Chapter 16, and NDS defines the duration of load factor for live load as 1.0, you technically need to use 1.0.

Pragmatically, I see this load on handrails/guardrails as a more instantaneous load - more akin to wind (1.6) or even impact (2.0) per the NDS.

 

[MiketheEngineer]

I agree with using 1.0 - mostly because of the importance or safety of this item. However, an argument could be made for using 2.0 - impact loading - but I wouldn't use it.

 

[Cadair]

When the American Wood Council (authors of the NDS) made a guide for decks, they used 1.6 for the handrails. This can be seen in the commentary of the following

http://www.awc.org/publications/DCA/DCA6/DCA6-09.pdf

 

[ash060]

IBC 1607.1.3 allows a 1/3 increase for stress. I know that it is not a load duration increase, but you might as well use it since the code allows.

 

[nutte]

I don't think you "technically" need to use 1.0 just because it's a live load. The NDS table defines the load duration factor in terms of length of duration (time), then provides "typical" loading scenarios where this might apply.

That said, the Prescriptive Residential Wood Deck Construction Guide (

http://www.awc.org/Publications/DCA/DCA6/DCA6-09.pdf)

recommends a load duration factor of 1.6.

 

[nutte]

Cadair beat me to it.

 

[JAE]

nutte - good point on the NDS appendix table vs. actually assigning load types to those durations. I would agree then with the 1.6.

 

[JAE]

I would use 1.0, though, on the connections.

 

[bob96]

Thank you all for thoughts and responses.

 

[woodman88]

The duration of load is based on how long the load is applied to the member, connections, etc. over the life of the members. This loading is cumulative over the life of the member. Assuming that the handrail is not replaced for ten years. I see the possibility of the 200 lb load being applied (10, 20, 30 seconds at a time) for more than the ten minutes allowed for by the 1.6 increase at some locations along the handrails. For this reason (when the use of the 1.0 factor was a problem) the maximum I would ever want to use is 1.25, a seven day duration factor.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.