UFC 4-023-03
25 January 2005
CHAPTER 2
PROGRESSIVE COLLAPSE DESIGN REQUIREMENTS
FOR NEW AND EXISTING CONSTRUCTION
For both new and existing structures, the Project Planning Team will develop
and provide the design criteria, which will include the Level of Protection, as determined
by UFC 4-020-01. This LOP is used to define the corresponding level of progressive
collapse design for new and existing construction as detailed in Section 2-1. Additional
design requirements common to all construction types and all Levels of Protection are
given in Section 2-2.
Chapter 3 "Design Strategies" provides the general requirements for applying
the Tie Forces (TF) and Alternate Path (AP) approaches. The overall techniques for
both the TF and AP approaches are the same for each construction type, but the details
vary with material type. Chapters 4 through 8 provide the material specific design
requirements. Finally, Appendix B provides insight into the development of these
approaches.
2-1
DESIGN REQUIREMENTS FOR NEW AND EXISTING CONSTRUCTION.
The details of the design requirements for each LOP for new and existing
construction are provided in the following sub-paragraphs.
2-1.1
Very Low Level of Protection Design Requirement.
A structure with Very Low Level of Protection must provide adequate
horizontal tie force capacity. The magnitudes of the horizontal tie forces vary with
construction type and with location in the structure, as specified in Chapters 4 through
8. The designer cannot use the Alternate Path method to verify that the structure can
bridge over an element with inadequate capacity. If a structural element does not
provide the required horizontal tie force capacity, it must be re-designed in the case of
new construction or retrofitted in the case of existing construction. This procedure is
illustrated in the flowchart in Figure 2-1.
2-1.2
Low Level of Protection Design Requirement.
The design of a structure with a Low Level of Protection must incorporate
both horizontal and vertical tie force capacities. However, if a vertical structural member
cannot provide the required vertical tie force capacity, the designer must either re-
design the member or use the AP method to prove that the structure can bridge over
the element when it is removed. For elements with inadequate horizontal tie force
capacity, the Alternate Path method cannot be used. In this case, the designer must re-
design the element in the case of new construction or retrofit the element in the case of
existing construction. This procedure is illustrated in the flowchart in Figure 2-2. The
magnitudes and locations of each tie force vary with construction type, as shown in
Chapters 4 through 8.
2-1
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