The nonlinear static force method and its dynamic increase factor (DIF) were investigated analysing steel frames subjected to column failure. The assessment was performed in terms of the ability of the nonlinear static method to predict the peak structural response observed in the dynamic analyses. The values of dynamic increase factor thus obtained were expressed as a function of the vertical displacement in the location of column removal.
Variability in these results is then assessed showing that they vary more significantly depending on variables such as the number of spans, the location of column removal, the number of building stories and the level of seismic design load. The values obtained were finally compared with the formulation of the dynamic increase factor proposed by GSA and based on the ductility factor. It was observed that using standard DIF formulae might lead to inaccurate results. In fact, these empirical formulae are based on the hypothesis of a constant value or a monotonic decreasing with ductility. On the contrary, in the cases where the hardening behavior of the catenary action is fully developed, the analytical curve of DIF first decreases and then increases with ductility.
