What Is a Damped Outrigger System?
A damped outrigger connects a tall building's core to its perimeter columns through energy-dissipating devices (viscous dampers) instead of rigid links — the outriggers engage the perimeter columns for stiffness while the dampers absorb wind and seismic energy. Conventional outriggers stiffen the tower but attract force; damped outriggers stiffen and damp simultaneously — the optimal tall-building lateral system for wind-controlled towers.
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How damped outriggers work
Outrigger trusses (or walls) at one or more mechanical levels tie the concrete core to the perimeter columns: core overturning becomes column axial force (the perimeter columns' tension/compression resists the moment — enormously stiff). Viscous dampers in the outrigger-to-column connections dissipate energy as the outrigger works — damping ratios climbing toward 5-10% supplemental. The result: a tower with the stiffness of outriggers and the damping of a damper system — drift and acceleration both controlled.
Design considerations
The structural engineer optimizes: outrigger locations (typically 1-2 levels — the top and mid-height, from the stiffness analysis), the damper properties (force-velocity relationship tuned to the wind and seismic demands), the differential shortening (core and columns shorten differently under gravity — the outrigger connections must accommodate the locked-in forces, often via delayed connection or adjustable details), and the column capacity (the outriggers deliver enormous axial forces — the perimeter columns and their foundations are designed for them).
Applications
Supertall towers (the damped-outrigger system appears in the world's tallest buildings — the stiffness efficiency is unmatched), slender residential towers (wind-comfort governed), and seismic high-rises (the damping reduces the seismic premium). The analysis is sophisticated (nonlinear damper modeling, construction-sequence analysis for the shortening) — the engineering fee reflects it. Peer review is standard for towers using the system.
The bottom line
Damped outriggers tie core to perimeter columns through viscous dampers — maximum stiffness plus supplemental damping for supertalls. Design for differential shortening and the columns' axial demands.
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