Investigation of the LS Level Hysteretic Damping Capacity of Steel MR Frames' Needs for the Direct Displacement-Based Design Method

Proper modeling of the Hysteretic Damping (HD) capacity of structural models at a desired performance level is the key requirement for reliable estimation of design base shears in Direct Displacement-based Design (DDBD) method. Priestley and his colleagues on the basis of their research, have proposed a formula to predict the HD capacity of Steel Moment-resisting Frames (SMRFs) which is presented in DBD12. The current study examined this relation and proposes a reliable equation for design of SMRFs using DDBD method at the Life Safety (LS) performance level and the Equivalent Viscous Damping (EVD) hypothesis. For this purpose, a wide range of SMRFs were analysed using linear/nonlinear static/dynamic time history methods under different loading conditions. The damping ratios of all models were calculated using Jacobsen's and Jennings's formulas and the procedure proposed by FEMA-440. The results show an exponential trend that diverges from the empirical formula presented in DBD12. Two new relations are proposed for hysteretic damping based on ductility and the ratios of the initial and equivalent periods.