Practical Means for Energy-Based Analyses of Disproportionate Collapse Potential

For several decades, the engineering profession has considered techniques to analyze the potential that structures could experience disproportionate collapse and to design them for greater resistance to such collapse. First interest in such design followed the partial collapse in 1968 of the Ronan Point building in London, a high rise residential structure that experienced full height collapse of a portion of the building following a relatively small kitchen-related gas explosion. Interest in collapse phenomena continued to build following the attack on the Alfred P. Murrah building in 1995 and has been at an apex since the collapses of the twin towers at the World Trade Center and the nearby World Trade Center 7 building in 2001. Presently researchers and engineers are studying structural performance during extreme deformations, systems to resist disproportionate collapse, and methods to analyze collapse potential. The goal is to develop techniques to accurately and cost efficiently assess collapse potential and to enhance robustness at appropriate cost. Analysis methods in common use include sophisticated dynamic, nonlinear modeling of structural systems with high-fidelity structural analysis computer software, and simplified approaches that are intended to capture the essential behaviors during collapse scenarios. Unfortunately, the sophisticated approaches require software not normally owned by design engineers, substantial experience in the modeling of collapse phenomena, and time and cost implications that cannot be supported by the present design fees and, indeed, are not warranted for many situations. Simplified analysis methods in common use are generally empirically based. Hence, they do not capture the essential behaviors of collapse mechanisms, and are of uncertain applicability for all but structural systems for which they have been calibrated. This paper presents two energy-based methods that capture the essential physics of collapse phenomena, and have potential to be developed into simplified procedures for collapse potential assessment.