25 January 2005
GUIDANCE FOR PROGRESSIVE COLLAPSE DESIGN IN
WOOD FRAME STRUCTURES
Wood frame structures are of interest to DoD designers because of their
economy and speed of construction. As presented in Chapter 7, tie force requirements
and alternate path analysis techniques are similar to those presented for other
construction materials. However, wood frame and "platform" type construction have
some significant differences. Wall and floor systems, while designed as load-bearing
elements, have significant diaphragm strength. Because of the unique nature of these
types of structures, further discussion of design approaches is warranted.
Wood frame construction in CONUS is generally limited to buildings of ten
stories or less. These buildings can be wood, composite or masonry sheathed, and can
be constructed entirely of a wood frame, floor and wall system, or can be a combination
of wood and steel or concrete frame systems.
Two approaches exist for resisting progressive collapse: Tie Forces and
TIE FORCES FOR WOOD FRAME CONSTRUCTION.
Internal horizontal ties, external wall ties, peripheral floor ties and vertical ties
can be provided in light wood framed construction using a combination of member
strength and supplemental mechanical ties. Member strength, mechanical (wood to
wood and metal to wood) connection strengths and fastener (nails, staples, screws, lag
screws, bolts and pins) strengths can be determined from appropriate design guidance
such as the American Forest and Paper Association (AF&PA) "National Design
Specification for Wood Construction", NDS-01, 1997 (NDS-01 1997). The supplemental
ties can consist of straps, hangers and other manufactured connection products.
Adequate tie forces must be developed through a combination of these members and
connections. Forces to resist collapse through diaphragm tension and floor plate action
may also be present, and are addressed in the next section dealing with the Alternate
To illustrate Tie Forces in light wood frame construction, a modern typical
wood frame barracks structure is investigated. The exterior appearance of the example
structure is shown in Figure F-1. The structure is 154 ft (e-w) by 60 ft (n-s) in plan, has
a ground and two upper floors (10 ft floor to floor height) and a wood truss roof system.
The exterior load-bearing walls consist of 2x6 southern pine studs on 16 in centers with
a single 2x6 floor plate and a double 2x6 top plate. Exterior wall columns consisting of