25 January 2005
WOOD DESIGN REQUIREMENTS
This chapter provides the specific requirements for designing a wood building
to resist progressive collapse.
Wood construction takes several forms in current practice. As described in
the 1996 version of AF&PA/ASCE 16-95, Load and Resistance Factor Design Manual
for Engineered Wood Construction, wood construction can be categorized as wood
frame, noncombustible wall-wood joist, and heavy timber. As most wood construction
used for DoD facilities falls under the wood frame category, this is the focus of these
Noncombustible wall-wood joist construction, such as masonry load-bearing
walls with wood floor and roof systems, is considered a composite system and requires
the application of both the requirements of this chapter and those provided for masonry
in Chapter 6. The floor system and roof system are required to meet the internal tie
requirements of this chapter, while the masonry walls are required to meet the tie
(vertical, peripheral, and wall) requirements or AP requirements of Chapter 6.
MATERIAL PROPERTIES FOR WOOD.
All over-strength factors for wood are equal to 1.0. In addition, the time effect
factor λ, shown in Table 7-2 and discussed in Appendix B, is equal to 1.
WOOD TIE FORCE REQUIREMENTS.
The following sections provide the necessary information to calculate the
required tie forces. An example showing the calculation of the required tie forces and
the design of connections and elements to resist tie forces is presented in Appendix F.
Wood frame construction is analogous to closely spaced columns and beams
with nominal tie resistance provided at each joist to wall stud junction. Peripheral,
internal, vertical, and horizontal ties to columns and walls are required. Structural
members and connections that are provided for other purposes may be regarded as
forming part or whole of the required ties.
As specified below, ties must, in whole or in part, be spread evenly in the
diaphragm or must be grouped at or in beams, walls or other appropriate positions.