Pulldown Analysis for Progressive Collapse Assessment

AbstractA new nonlinear static alternate path analysis technique coined pulldown analysis is presented as an easy-to-implement alternative to the existing pushdown analysis for assessing the load redistribution capability of a building after a critical structural element has been suddenly removed. Unlike the pushdown analysis where gravity loads within the affected bays of a building are directly amplified, the pulldown analysis is associated with a downward force that is statically applied at the removed element location. This static pulldown force is equal in value to the axial compression force in the to-be-removed column of the intact frame multiplied by a dynamic increase factor (DIF), which aims to generate the best match of the peak dynamic responses of a damaged building through a nonlinear static analysis. A seismically designed nine-story steel moment frame is used as an example to illustrate the pulldown analysis procedure. Results from progressive collapse assessment of the example frame using...