On the Lateral Response of EC8-Compliant X-CBFs

The second generation of Eurocode 8 (EC8-1-2) introduced revised design rules for dissipative concentrically braced frames (CBFs). This paper investigates the seismic response of low- and medium-rise X-CBFs designed according to EC8-1-2 to provide an evaluation of the effectiveness of the code design provisions. Three- and six-story frames were designed for different seismic action intensities in medium- (DC2) and high-dissipative (DC3) ductility classes. Their lateral response was evaluated through nonlinear static analyses performed on global numerical models. The capacity curves were derived to determine the target displacements at the Damage Limitation (DL), Significant Damage (SD), and Near Collapse (NC) limit states. The calculated behavior factor components were consistent with the corresponding EC8 q-values. The frames developed the intended dissipative mechanism, with braces buckling in compression and yielding in tension at both SD and NC limit states. Moreover, braces in DC3-compliant frames exhibited incipient buckling at the DL limit state. Capacity design prevented yielding of beams and columns. Despite adequate cross-sectional resistance, the EC3 member stability checks were generally not satisfied for first-story columns in both ductility classes. In DC3, peak column moments exceeded the design value, although their distributions were less severe than the uniform shape assumed in the design. The EC8-1-2 design rules provided satisfactory system-level responses, while the column stability verifications were not consistently satisfied.