Analysis and Design Methods for Improved Stability of Two-Tiered Steel Eccentrically Braced Frames with Continuous I-Shaped Links

A set of seismic analysis and design requirements are presented to improve seismic stability of steel two-tiered eccentrically braced frames (EBFs) with I-shaped link beams. The proposed requirements include strength, stability, and stiffness provisions for braces, intermediate beams, and columns. In particular, these requirements aim to make use of intermediate beams to limit out-of-plane deformation of diagonal braces, torsionally brace the link beam in the intermediate level using diagonal braces, utilize column stiffness and strength to brace the intermediate beam out-of-plane, estimate and account for in-plane bending demands of the columns due to uneven yielding of the links, and control inelastic link rotation. The proposed special analysis and design requirements for two-tiered steel EBFs prevent excessive out-of-plane deformation of the intermediate beam and columns, promote sequential yielding of link beams, and limit inelastic rotation of the link in the tier experiencing the largest lateral deformation. The proposed requirements are demonstrated for a case study two-tiered EBF. Nonlinear static and dynamic analyses are performed to evaluate the seismic response of the case study frame against the frame designed without special design provisions and to validate the proposed requirements.