Estimation of system-level ductility demands for multi-story structures

System-level ductility is an essential factor for earthquake resistant design of structures. It is related to the response modification factor (or force reduction factor), commonly used in aseismic design procedures. The ductility demands for single-degree-of-freedom structures or individual structural members can be determined easily. However, there is no established method of determining the ductility demands for structural systems. The object of this study is to develop a method for the estimation of the ductility demand at the structural system level. The validity of the proposed method has been examined for several cases of different structures and different earthquake excitations.