Alternate Path Method in Progressive Collapse Analysis: Variation of Dynamic and Nonlinear Load Increase Factors

In performing alternative path analyses for checking the potential of a structure to progressive collapse, most designers often choose static procedures, which tend to be simpler and less labor demanding. As progressive collapse is a dynamic and nonlinear event, the load cases for the static procedures require the use of factors to account for inertial and nonlinear effects. A number of inconsistencies have been identified in the way the existing guidelines applied dynamic and nonlinear load factors to their static approaches. As part of an existing effort to update the existing guidelines, this study looked into the behavior of a variety of reinforced-concrete and steel moment-frame buildings to investigate the magnitude and variation of the dynamic and nonlinear load increase factors. The study concluded that the factors in the existing guidelines tend to yield overly conservative results, which often translate into expensive designs and retrofits. This study identified new load increase factors and proposes a new approach to utilize these factors when performing alternative path analyses for progressive collapse.