Design

Substituting Fire Rated Wood Truss Assemblies For Light Gauge Steel

Question: 

We recently received bids on a school project, which referenced UL P523. This assembly used light-gauge steel trusses. We noted on the drawing that we could accept an alternate design using wood trusses in lieu of light-gauge steel framing, if the alternate design could meet the fire ratings.

Design Loads Vs Typical Loading Conditions

Question: 

The Corps' guide spec for wood construction requires the drawings to indicate the design forces on each truss member for the worst loading condition. Loading conditions, of course, can include wind, snow build up, and unbalanced loading, to name a few. Many A/E firms submit drawings lacking these member forces, but instead show typical loading conditions. What does the wood truss fabricator want to see – truss diagrams with maximum loads on each member? Or would he prefer to design the truss from many required loading diagrams?

Truss Bracing At Supports

Question: 

I almost always see wood trusses erected with no stability bracing at points of support. It seems to me that common sense and section 3.3.3.4 of The American Wood Council’s National Design Specification for Wood Construction (NDS) require that lateral support be provided at points of bearing. Plywood decking doesn't provide any more restraint for a wood truss than it does for a roof joist. I doubt if it was a concern with short span trusses having 4 in.

Storage Loading

Question: 

How much weight can a wood truss hold, when it’s made with 2x4 material and spans 36 ft. with a 4/12 pitch. I would like to hang things from the ceiling and am wondering if it is safe. I live in an area where there are heavy snowstorms. Also, how much exposure to the weather can a truss handle before there is a problem?

T-bracing

Question: 

The truss industry maintains that the design of truss roof and floor system permanent bracing is the responsibility of the building designer. System permanent bracing covers the entire structure and all bracing element interactions.

Purlin Design

Question: 

Do you have information on purlin grades and species to meet 50 psf top chord live load using 2x4s on edge 24 in. O.C. over trusses at 6 ft. O.C.?

Determining Earthquake Loads

Question: 

We are currently developing a project which specifies “Seismic Design Category C.” We are an East Coast truss manufacturer and have not encountered seismic requirements before.

Truss Blow Down

Question: 

If trusses blew down from insufficient temporary bracing and the contractor put them back up without the knowledge of the truss manufacturer and gave the truss manufacturer a letter stating that the trusses were okay, is that sufficient? Do you know of any truss manufacturer who would accept this?

Create A Ceiling Vault In Existing Rafter Roof

Question: 

Is it possible to retrofit a standard rafter/joist style roof to a scissors truss configuration without replacing the existing construction?

Repairs To Field Modified Damaged Trusses

Question: 

As a home inspector, I have recently inspected an existing home with an attic truss system installed. Several of the truss web members have been cut away to allow access to an attic-mounted heating system. Can you recommend repairs to a truss with cut web members?