Improved Eurocode‐based design of tall buildings with braced core and outrigger systems

Abstract

Previous research has shown deficiencies in the Eurocode provisions for producing reliable designs of tall steel buildings with mega‐braced core and outrigger systems, due to a significant underestimation of Interstorey Drift Ratios (ISDR) and seismic demands in primary members. To address this limitation, the present study introduces a supplementary factor, the Dynamic Amplification Factor (DAF), which can be directly applied in the preliminary design stage without modifying the EC8 procedure. The proposed DAF provides a rational means to more reliably consider the true seismic demands during a seismic event. It should be used to upsize the cross‐sectional dimensions of structural members in the lateral load‐resistance system and to adjust axial force demands in non‐dissipative members. The proposed factors were assessed through extensive Nonlinear Time History Analyses (NLTHA) under a suite of rare earthquake ground motions. For this purpose, detailed 3D numerical models were built in OpenSees, accounting for nonlinear material properties and geometric nonlinearity. The results demonstrated that the DAF is height‐dependent, with its influence becoming more pronounced for taller structures. The study also demonstrated that applying the DAF significantly enhances the structures' seismic performance and helps meet the ISDR requirements at the characteristic seismic intensities, thereby improving the reliability of the seismic design.