Ω* method: An alternative to Eurocode 8 procedure for seismic design of X-CBFs

The paper validates Ω* method proposed by some of the authors in previous papers for design of X-Concentric Braced Frames (X-CBFs). This method was obtained relaxing some of the requirements of the method provided by the European seismic code (Eurocode 8, EC8). Therefore, Ω* method is conceptually similar to that of EC8, which makes it easy to be incorporated into EC8 and to be embraced by the European structural designers. The paper analyses the seismic performance of a set of X-CBFs designed both according to EC8 and Ω* methods. Several buildings characterised by different numbers of storeys, numbers of bracings in plan and by different bay spans are considered. Non-linear dynamic analyses have been carried out by the computer code CLAP to evaluate the seismic performance of the analysed buildings. The results of the numerical analyses show that the Ω* method: (i) reduces the unnecessary global overstrength which typically is found in structures designed in accordance to EC8 design rules; (ii) leads to an optimized structural design; (iii) ensures a local and global ductility of braces under cyclic actions comparable to EC8 design solutions; (iv) has a greater “flexibility” in the design process.