Proposal of lateral forces for capacity design of controlled rocking steel cores considering higher mode effects

Abstract

Controlled rocking steel cores (CRSCs) may suffer progressive collapse because of inadequate structural design and loss of re-centering action. While the CRSCs displace in the first-mode frequency, the demands of their members are strongly affected by higher modes. Conventional lateral load distributions, such as the uniform and inverted triangular, cannot predicate the design forces of CRSCs. This paper proposes new lateral loads for the design of CRSCs. Continuum cantilever beam analogy is utilized to formulate the higher-mode contribution. The application of the lateral loads is validated through illustrative examples of low- and mid-rise CRSCs. Results supported by nonlinear time response analyses demonstrate the effectiveness of proposed formulae for reliable estimation of seismic demands. The proposed lateral forces are readily applicable in commercial software without gap modeling at the base boundary conditions of CRSCs.