Improved value for load increase factor in disproportionate collapse


Current design guidelines for General Service Administration (GSA 2003 & 2013), United Facilities Criteria (UFC 2009) adopt the alternate path method for disproportionate collapse-resistant structures design. In the alternate path design approach, a critical structural component (typically a key column) is suddenly removed from the system and the ability of the other components of the structural system to withstand the added forces is examined. This can be done using linear or nonlinear static analysis (LSA and NSA) as well as the nonlinear dynamic analysis (NDA) method. In the dynamic method, the inertial forces are directly considered in the analysis through the equations of motion. However, a Load Increase Factor (LIF) is introduced in the static analysis methods to account for the modifications of dead and live loads due to the unaccounted for dynamic effects. The LIF value recommended by GSA (2003) is 2.0, while it is derived based on recommended equations adopted by GSA (2013) and UFC (2009). In this study, dynamic analyses of a multi-story building subjected to sudden column removal are conducted taking into consideration geometric nonlinearity and material inelasticity. Based on these analyses, the LIF is computed and compared with design recommendations. The results from this study indicate that the current values of LIF need to be re-evaluated in order to achieve more economical designs.

Publication Title

Structures Congress 2015 - Proceedings of the 2015 Structures Congress