Seismic design of two-storey X-bracings

Two-storey X-bracings are becoming very popular in European practice, owing the possibility to reduce the bending demand typically observed on the brace-intercepted beam in V and inverted-V configurations. However, they are not properly addressed within the current Eurocode 8, and specific design provisions are missing. In this paper the main critical issues affecting the seismic behaviour of two-story X concentrically braced frames are discussed. With this regard, seismic design criteria provided by both US and European codes for concentrically are summarized and critically discussed with specific reference to two-story X configuratio