Chapter 11 Lightweight Word Truss Collapse Flashcards
What are the two types of wood truss systems
heavy timber truss
lightweight wood truss
building code defines heavy timber roof construction as wood dimensions at least
4 inches wide
6 inches deep
lightweight wood truss incorporates wood members which can be as small as
2 inches wide
4 inches deep
sheet metal fasteners only penetrate the wood….
1/4” - 1/2”
By engineering calculations and practical firefighting experience lightweight trussed rafters may be expected to collapse after
10 minutes in a fully developed fire
In any structural elements, the critical area subject to failure during fire is
the point of contact
the most serious deficit in the surface fastener connecting lightweight wood truss is ___
the insufficient depth of penetration, half-inch
even if the fire is not of sufficient intensity to try the word heat from the flames can warp the thin sheet metal causing
to curl up and pull away from the truss
Aside from insufficient depth of penetration and warping due to heat from flames, what other deficits do surface fasteners have
- lightweight wood trusses are prefabricated rough handling can loosen minimal surface fasteners before installation
- moisture and chemicals to treat wood can cause corrosion on fasteners
how does lightweight wood truss allow fire to spread easily
it allows lateral movement of the fire in comparison to solid wood beams which would passively hold fire better in concealed spaces… truss have open design
what is the recommended strategy for fighting fire in buildings with lightweight wood truss floors or roof
1.
what is the recommended strategy for fighting fire in buildings with lightweight wood truss floors or roof
- contents fire- extend line and extinguish content (sofa)
- structure fire- in the fire involves a structuring is burning through the concealed roof or floor spaces, defensive strategy
