Defining Where Progressive Collapse Protection Is Needed

Abstract

The U.S. Department of Defense (DoD) mandates progressive collapse protection for all new military buildings that are three or more stories in height. Detailed information regarding acceptable design approaches are provided in relevant Unified Facility Criteria (UFC) documents. These documents are periodically updated as needed. Initially, when UFC progressive collapse criteria were released post-9/11, the extent of protection was typically limited to the building exterior. In 2009, the extent of protection became more dependent on internal security measures. Specifically, internal areas designated as ‘unsecured’ required progressive collapse protection. Because the term ‘unsecured’ is not well defined, this requirement can cause cost increases to a project if not resolved at the earliest opportunity. In this paper, a legal dispute concerning the extent of the progressive collapse protection required for a military facility is used as a case study to illustrate the issues that can arise. UFC requirements and documents pertaining to the acceptable methods of progressive collapse and the locations of this protection are outlined. INTRODUCTION Progressive collapse mitigation measures reduce the chances of catastrophic building collapse due to the loss of a disproportionately small part of the building structure failing. The intent of progressive collapse requirements is to allow the damaged building to remain standing long enough for those inside to safely evacuate. The UFC antiterrorism documents define the following approaches to address progressive collapse: 1 Tie Force Method. This is a way to ‘tie’ the building together by allowing the floors, walls and columns to stretch and sag without failing if a localized part of the building is lost. 2 Enhanced local resistance. Key parts of the building are designed to be able to accept larger loads than they do under normal circumstances. 3 Alternate load path. This provides an alternate way for the loads to be transmitted around a failed column or wall. Forensic Engineering 2015 495