Overview of the Revised DOD Progressive Collapse Design Requirements

Abstract

In the three years since Unified Facilities Criteria (UFC) 4-023-03 Design of Buildings to Resist Progressive Collapse was first published in January of 2005, various omissions, ambiguities, and opportunities for improvement were identified by civilian and government designers and engineers. A significant revision to the Progressive Collapse UFC was initiated in the Fall of 2006 and was recently completed, during which a number of significant improvements were made. Occupancy Categories (OCs) similar to those in ASCE 7 Minimum Design Loads for Structures are used to define a building's progressive collapse design requirements; previously, military definitions of levels of protection were used. Indirect design methods for enhancing load redistribution capacity with tie forces and direct design methods using alternate path and specific local resistance continue to be employed but with revisions. The alternate path method now includes dynamic and load increase factors that are based on careful analysis of the inertial and nonlinear aspects of load redistribution. Structural response criteria are specified in terms of force- and deformation-controlled actions, similar to ASCE 41-06 Seismic Rehabilitation of Existing Buildings . A non-threat specific, local hardening procedure was developed and implemented, to insure ductile behavior of critical elements without significant additional cost, for new construction. Finally, a brief overview of three example problems is provided.