Mitigation of higher-mode flexural demands in controlled rocking walls using outriggers

Controlled rocking walls have been studied extensively to improve the seismic performance of buildings; however, this mechanism increases higher-mode participation and shifts flexural demands to upper stories, limiting their application in tall, slender structures. To address this limitation, this study evaluates the effectiveness of damped outriggers in reducing higher-mode flexural amplification. In this system, the outrigger connects the rocking core wall to the perimeter mega-columns using dampers that produce a counteracting moment and provide supplemental energy dissipation at the outrigger level. A reduced-order nonlinear OpenSees model, validated against large-scale shake-table testing, is used to perform a parametric study considering outrigger location, stiffness, strength, and reduction factors. The results show that higher-mode amplification increases with building height and decreasing base moment capacity. Outriggers significantly reduce amplified upper-story demands and base rotation, with rooftop configurations providing the most consistent mitigation. Outrigger stiffness primarily controls the deformation profile and drift response, while strength governs the magnitude and localization of flexural demand redistribution. A key finding is that near-elastic or very strong outriggers can induce localized moment amplification, whereas moderate-strength outriggers that yield produce more uniform redistribution. Higher-mode flexural demand is relatively insensitive to outrigger strength across most configurations. These results show that damped outriggers can extend the applicability of controlled rocking systems to taller buildings by reducing higher-mode amplification and base rotation demands, while avoiding inefficient strength-based design. The findings provide practical guidance for proportioning outrigger stiffness and strength and highlight that controlled yielding, rather than maximum strength, governs effective performance.