Pre-Engineered Wood Truss Design Question
Pre-Engineered Wood Truss Design Question
(OP)
How do pre-engineered wood truss engineers design the bottom chord? If the drawings specify that the bottom chord should carry an uniform load... does the design engineer assume that the hung load will be screwed into it? How does the industry approach this?
"We shape our buildings, thereafter they shape us." -WSC






RE: Pre-Engineered Wood Truss Design Question
RE: Pre-Engineered Wood Truss Design Question
You could always tell them on you plans what you intend to do to the bot. chord, so they can design accordingly; or so they can tell you how to accomplish what you want. They do not like to see the bot. chord riddled with nails and screws, etc. They don’t want your activities splitting or otherwise reducing the strength of the bot. chord. It is generally the best and strongest piece of lumber in the truss and is fairly highly stressed, in tension.
RE: Pre-Engineered Wood Truss Design Question
But if you plan on any penetrations other than fasteners at 3-4" o.c., that would be something to coordinate with the truss designer, or rather avoid.
RE: Pre-Engineered Wood Truss Design Question
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RE: Pre-Engineered Wood Truss Design Question
RE: Pre-Engineered Wood Truss Design Question
RE: Pre-Engineered Wood Truss Design Question
If it is a typical attic space then the bottom chord loads are applied conventionally without much direction from the EOR or truss design engineer. The drywall is either nailed to the bottom chord or to hat channel. The load might also includes lighting, ductwork, insulation and perhaps light storage on plywood planks.
If the loads include fire suppression, ceiling mounted fixtures or anything more than 10 or 20 psf then the bottom chord will require sistering or strong-backs to support the loads and additional fasteners. These are usually designed by the EOR or sub-trade as long as the truss design engineer has anticipated the superimposed loads.
Aside from showing the MAGNITUDE & LOCATION (not shouting) of point loads or uniform loads on the truss design drawings, the truss design engineer would almost never give any specific attention to HOW the loads were being connected to the truss and whether or not the bottom chord was compatible with the connectors used. Secondary/localized strengthening of the bottom chord to accept fasteners or specialized hangars would fall to the EOR or to the sub-trade.