Multi-level performance-based optimisation of steel moment-resisting frames equipped with rotational friction dampers

This research introduces a novel approach for multi-level performance-based seismic design optimisation of steel moment-resisting frames equipped with Rotational Friction Dampers (RFDs). The concept of Uniform Damage Distribution (UDD) is adopted, for the first time, to optimise the complex behaviour of RFDs aiming to meet Life Safety (LS) performance target under Design Basis Earthquake (DBE) events with a minimal amount of damping required. The proposed approach fully integrates the nonlinear characteristics of the dampers, enabling optimum design solutions under dynamic loading conditions with low computational cost, while the use of numerical models validated against established experimental and analytical benchmark results ensures accurate representation of RFD behaviour. The results demonstrate that the optimised frames exhibited up to 70% less total friction forces compared to their conventionally designed counterparts with uniform damper distribution, while the number of required dampers is also reduced. The adequacy of the optimised design frames was then evaluated under a set of 15 real spectrum-compatible earthquakes. It is shown that to consider the uncertainty of the input earthquake records, structures should be optimised using a set of earthquake records rather than a single event, especially in the case of tall buildings. The method was then expanded to consider multi-level performance objectives, by adding a second criterion to achieve collapse prevention (CP) performance level under Maximum Considered Earthquake (MCE) events. Through incremental dynamic analysis (IDA), it is shown that the proposed multi-level optimisation method consistently reduced global structural damage compared to uniform load distribution and the distribution obtained from single-level optimisation by up to 55% and 40%, respectively, subjected to earthquakes with different intensity levels.