UFC 4-023-03
25 January 2005
1-3.4
Existing Design Guidelines.
1-3.4.1
British Standards.
England was the first nation to address progressive collapse explicitly in its
building standards. The development was initiated by the collapse of the Ronan Point
apartment building in 1968, and further motivated by the IRA bombing campaign. The
British Standards employ three design approaches for resisting progressive collapse:
Tie Forces (TF). This indirect design approach enhances continuity, ductility,
and structural redundancy by requiring "ties" to keep the structure together in
the event of an abnormal loading.
Alternate Path (AP). This direct method requires that the designer prove that
the structure is capable of bridging over a removed structural element and
that the resulting extent of damage does not exceed the damage limits. The
missing structural element is any element that cannot provide an adequate
vertical tie force.
Specific Local Resistance (SLR). This direct method requires that, for any
structural element over which the building cannot bridge, the element must be
designed as a "key" or "protected" element, capable of carrying a static
pressure loading of 34 kN/m2 (5 psi).
The British have employed this combined approach for almost 30 years and
the effectiveness of the strategy has been illustrated in a number of deliberate attacks
on buildings, as discussed in The UK and European Regulations for Accidental Actions
by D.B. Moore (Moore 2003). Recent proposed modifications to the British Standards
and draft Eurocode standards include a risk assessment procedure that will better
correlate the level of design for progressive collapse to the particular structure.
1-3.4.2
United States Civilian Standards.
While general design guidance for reducing the potential of progressive
collapse are discussed in ASCE 7-02, no quantifiable or enforceable requirements are
put forth. Likewise, none of the major United States building codes (e.g., International
Building Code, Uniform Building Code, Building Officials and Code Administrators) nor
the structural design codes (e.g., American Institute of Steel Construction, American
Concrete Institute, The Masonry Society, American Iron and Steel Institute, American
Forest and Paper Association) provide specific design requirements.
1-3.4.3
United States Government Standards.
Design guidelines for resisting progressive collapse have been published by
the Department of Defense (DoD) in 2001, in the Interim Antiterrorism/Force Protection
Construction Standards--Guidance on Structural Requirements (ITG 2001), and, by the
U.S. General Services Administration (GSA) in 2003, in the Progressive Collapse
Analysis and Design Guidelines for New Federal Office Buildings and Major
1-3
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