fire rating capacity reduction

Can you post a clearer image or a link to the UL assembly, at least to me the image above is hard to read.

This is a topic I'm very interested in because we deal with UL's and wood stud wall assemblies and these issues quite a bit and it only seems to be getting worse. Sadly many engineers appear to be missing these kinds of reductions.

here is the link:

Just a bump to this - anyone have input or a resource to dig into this more?

When using ASD I would use the full load (1.0D + 1.0L). CH16 of the NDS provides char depths and stress increases to compare timber members to ASD loads. When using LRFD I've not used load reductions like the image you show but I have used the Extraordinary Load Combos in ASCE 7. I've not heard of a fire rated truss from a typical truss mfr. If it where a heavy timber custom truss it could be rated. Typically it's just an entire assembly that needs a rating though.

Yea the main thing I am referencing is the assembly that is rated has the statement that a load reduction is required if using limit state design. If you look up UL L528 for example it has that statement. When I asked UL they said the truss manufacturer would have to take a strength reduction into account and they had no guidance to offer. It was unclear if the ASD for wood is considered a limit state design method rather than a working stress design method in the same way this all affected structural steel.

I read it as you do, using ASD you don't have the reductions. It appears that they are providing a factor to bring LRFD results closer to that of ASD.

Fire design in itself is a confusing mess to get into, especially when architects are changing UL assemblies constantly. We mostly deal with it with wall assemblies where you have the IBC reduction to 78% for a min le/d but then have UL assemblies that meet the IBC but give further reductions, sometimes a limit to axial capacity or even 42% of design strength.