# Truss manufacturer drawings unclear

I am currently looking at a set of truss layouts produced by our truss manufacturing partner for a residential building project. I have reason to believe these layouts are generated using Alpine (Intelliview?) software. In any case, the design summary contains abbreviations which I cannot understand since I do not have a copy of the software. Please see below:

According to this document R, U and W stand for reaction due to design load, uplift due to wind load and bearing width, respectively. TCLL, TCDL, BCLL and BCDL stand for top chord live load, Top chord dead load, Bottom chord live load and bottom chord dead load. However I cannot for the life of me determine what Rw, Rh, RL and NCBCLL stand for. Any ideas?

• Where are you located? – grfrazee Mar 15 '16 at 14:31
• This is in California. I dont think thats too relevant though since this is software output. – user32882 Mar 15 '16 at 14:33
• They might be using a local building code as input to the program, so location could be relevant. – grfrazee Mar 15 '16 at 14:41
• OP, did you contact and ask the manufacturer? What was the answer about Rw, Rhode, RL, and NCBCLL. – William S. Godfrey- S.E. Mar 18 '16 at 0:56
• I did not contact the manufacturer, although I did find that NCBCLL stands for non concurrent bottom chord live load – user32882 Mar 19 '16 at 14:48

However I cannot for the life of me determine what Rw, Rh, RL and NCBCLL stand for.

Given that the values Rw, Rh, and RL are under a Maximum Reactions header, I assume that they are the reaction components of:

• Rw = reaction force due to wind (or possibly water?)
• Rh = reaction force due to horizontal load (or possibly hydrostatic?)
• RL = reaction force due to live load

These are given at support points $A$ and $I$.

I think NCBCLL is the construction live load, but I don't know what NCB stands for.

Here's another Alpine output sheet that might be of use as a reference.

There are upper and lower dimensions for each portion of the span. I would like to understand why there are up to 4 distinct dimensions for each span.

It's hard to tell exactly from the drawing, but these dimensions seem to be working from different sides of the truss members. The dimensions on the top seem to be to the left side of the vertical members and the bottom dimensions seem to be on the right.

I'd ask your truss supplier to clarify. If they're using the software, they should know what the output means.

• I agree. I think Rw is likely wind. Rh is interesting. I wouldn't think it's reactions from hydrostatic loading on prefab wooden trusses. Though I've seen weirder things. Maybe it's their catchall variable for "not-wind-lateral-forces." It also seems a little odd to me that there is no seismic reaction. I'd expect at least some, maybe small, seismic loading and therefore reactions. Especially in California. Maybe they're assumed enveloped by the wind reactions? Maybe these trusses support a diaphragm that isn't considered to act as part of the lateral force resisting system? – William S. Godfrey- S.E. Mar 15 '16 at 15:15
• @WilliamS.Godfrey, I was thinking hydrostatic in terms of ponding on the roof, but I think it's more likely that it's a catch-all for misc. horizontal forces. Good point about seismic, especially with the OP being in California. – grfrazee Mar 15 '16 at 15:17

Source: SBC Magazine

Recently was looking for this same information. Found this thread and then the article. Hope this is helpful in the future!

NCBCLL is IBC Code for Non Concurrent Bottom Chord Live Load, used for uninhabitable/inhabitable attic space live loads @ 10/20 PSF through Alpine ITW