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? Since I already paid my A/E for a design, how much does a truss manufacturer charge for this service?
Answer:
We agree with the Corp's guide spec for wood construction: the building designer should list the required design loads. SBCA’s TTB – Standard Responsibilities in the Design and Application of Metal Plate Connected Wood Trusses outlines the responsibilities of the owner, building designer, contractor, truss manufacturer, truss designer, and others in the design process. According to the Truss Plate Institute's ANSI/TPI 1, the building designer is responsible for determining the location, direction and magnitude of all dead and live loads applicable to each truss, including but not limited to: roof, floor, partition, mechanical, fire sprinkler, attic, storage, wind, snow drift, and seismic. Therefore, it is not enough for the building designer to present only typical loading conditions and have the truss designer or someone else determine the applicable design loads.
As for your question about service charges, SBCA is a trade association that represents truss manufacturers all over the country. As such, we don’t actually perform truss design and can’t give a definitive answer to your question. Check out our Members Section for truss manufacturer listings – one of our members would be more than willing to assist you with your truss design.