The Influence of the Force Distribution on the Seismic Design of MRFS by TPMC

Abstract In seismic design, it is often economically unfeasible to ensure all structural elements behave in a ductile manner. Therefore, a structure typically comprises both ductile and brittle elements, with capacity design principles ensuring that brittle elements are protected by promoting the yielding of ductile components. One of the key challenges in achieving global collapse mechanisms in moment‐resisting frames (MR‐Frames) is the shifting of the contraflexure point in columns during seismic events. This phenomenon alters the distribution of bending moments, making it difficult to predict failure patterns using simplified design approaches, such as the beam‐column hierarchy criterion prescribed in Eurocode 8. While this criterion helps prevent “soft storey” failures, it does not guarantee a global collapse mechanism. For this reason, in the last years, an alternative design procedure has been proposed: the Theory of Plastic Mechanism Control (TPMC). TPMC is applied to ensure that plastic hinges occur only at beam ends, while columns remain elastic, except at the base of the first storey. In this study, the main aim is to evaluate the influence of different lateral force distributions on the seismic design derived by TPMC. In particular, a 6‐storey steel frame has been designed according to TPMC and by considering different lateral force distributions derived by the main seismic codes (e.g., Eurocode 8, IBC 2012). Then, the seismic performance has been evaluated using pushover and Incremental Dynamic Analyses (IDA) on recorded earthquake accelerograms. The results confirm the effectiveness of TPMC in achieving the desired global collapse mechanism, even when considering different lateral force distribution assumptions.