A proper estimation of inelastic dynamic increase factor in support-loss experiments

Dynamic increase factor (DIF) is usually approximated as the ratio of maximum to neutral response in dynamic support-loss experiments. However, this neutral-based calculation may underestimate the real DIF for elasto-plastic response. In this study, an analytical formulation is thus proposed to correct the neutral-based DIF based on measured dynamic response. Accuracy of the analytical formulation is verified with the results of a small-scale experiment. An iterative procedure, which is validated by the experimental results, is suggested for practical application of the correction approach. Its application to sudden support-loss tests of prototype buildings is demonstrated with numerical simulation for two model frames. The analysis results indicate that the corrected DIFs may be approximated to the real DIFs in most cases. Due to the coupled vertical oscillation under corner column loss, the correction approach is more favorable for interior column loss situations that are dominated by a single mode. The ductility demand obtained from the iterative procedure may serve as an indication of structural damage under column loss.