Non-Linear Dynamic Alternate Path Analysis for Progressive Collapse: Detailed Procedures Using UFC 4-023-03 (Revised July 2009)

摘要

In July of 2009, The US Department of Defense (DoD) released the newly revised version of the UFC Design of Buildings to Resist Progressive Collapse. The new UFC incorporates both direct and indirect design procedures. The main direct design procedure is the Alternate Path (AP) method, in which a structure is analyzed for collapse potential after the removal of a load bearing vertical component. Different analytical procedures may be used for AP, including Linear Static (LS), Nonlinear Static (NLS), and Nonlinear Dynamic (NLD). Significant changes have been made to AP methods for analysis in the new criteria which result in less conservative and more efficient structural components. Typically, when doing AP analyses, designers often choose static procedures which tend to be simpler, requiring less labor. However, progressive collapse is a dynamic and nonlinear event, and the load cases used for the static procedures that account for inertial and nonlinear effects tend to add conservatism to final design. The procedures in the criteria, from NLS to NLD, offer analysis procedures of increasing complexity and time investment, but offer a significant return of increased design efficiency. This paper presents a detailed example of how to properly perform an NLD AP analysis on a building following the guidelines in the new UFC and the advantages in the final design when compared to the results of an LS analysis.