Engineering

I recall seeing a design recommendation several years ago regarding installation of hanger nails above the neutral axis of the bottom chord of a plated girder truss. The intent was to avoid dumping large loads into the bottom chord, below the neutral axis. Can you tell me where I can find this information?

I have recently heard of a problem with fire-retardant-treated wood (FRTW) trusses that were manufactured and installed in 1965-1980. I was searching for more information, since my job involves the protection of property in our member school districts. I had heard that the trusses make of FRTW during that time period can or will become corrosive to the hardware and the trusses will fail.

We have a local builder wishing to use floor trusses with a 2-hour assembly. I have shown him the 2-hour design on pages 17-27 of the second edition of SBCA’s Metal Plate Connected Wood Truss Handbook. Is this assembly UL approved? If so, what is the design number?

Is finger-jointed material allowed in the manufacturing of trusses?

Some building designers believe that gable end webs need to be L-braced to 90% of the web length, which sounds fine. However, they spec that scissors gable end webs need to be braced to 100% of the web length. That means that in the field they are notching the braces to fit around top and bottom chords – you can imagine how difficult that can be. Is that necessary or even the intent of the web L-bracing?

Can you explain drag loads and how to calculate a drag load pertaining to roof trusses?

Some truss lumber repair nailing patterns call for 16d common nails. Most nail guns do not support 16d nails, but have an equivalent to a 12/10d nail. Is there a substitution guide or ESR report that could help us?

I am a structural engineer designing pool cage structures that are typically attached to the house at the fascia board. Sometimes, the structure is attached where trusses are behind the fascia board and other times there is a framed gable end overhang. Do you know of any information concerning this additional load on the trusses or overhang under design wind loads? Is there a limiting distance on the amount of overhang? I know trusses are designed for certain uplift and the pool cage will add to this uplift at design load, but what about the gable end overhangs?

Is it the responsibility of the truss manufacturer to provide a sealed layout drawing for roof trusses?

I have a four-year-old house with glued open-web trusses. Both the truss manufacturer and the builder have admitted to me that the trusses were installed wrong. I have a problem with the suggested repair. I have hired a structural engineer and he suggested installing a 2x10 between each truss and removing the old truss. This would have to take place on both the first and second floors because all the trusses were installed wrong. The manufacturers want to install six strongbacks on each floor, hoping this will tighten them up.