On the use of the half-power bandwidth method to estimate damping in building structures

The objective of this note is to assess the accuracy of the half-power bandwidth method for the estimation of damping ratios in single- and multi-degree-of-freedom structures with linear viscous damping including those that do not possess classical normal modes. This is done by performing some numerical experiments involving single- and multi-degree-of-freedom structures. It is found that the use of the half-power bandwidth method in its classical form may lead to significant errors, while a third order correction to this classical form provides conservative and more reliable results. It is also found in conjunction with this correction that application of the half-power bandwidth method should be performed to the acceleration frequency response transfer function of the structure on a mode-to-mode basis and that its damping ratio estimates for higher modes should always be viewed with caution.