What Is a Rocking Wall System?
A rocking wall system lets concrete or timber walls rock on their foundations during an earthquake — lifting at the base and recentering afterward — instead of yielding and sustaining damage. Post-tensioned tendons clamp the wall to the foundation; the wall rocks, the tendons stretch elastically, and gravity plus the tendon force pull the wall back to plumb. Damage-free seismic performance: the building recenters itself.
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How rocking works
Conventional shear walls yield at the base (plastic hinge — damaged, needing repair). Rocking walls are designed to uplift: the base connection allows rotation, vertical post-tensioning tendons provide the restoring force, and energy dissipators (replaceable steel fuses) absorb the earthquake energy. After the shaking, the tendons pull the wall back — residual drifts near zero. The structure survives the earthquake without the damage conventional systems accept.
Design requirements
The engineer designs: the rocking interface (armored base — steel plates preventing concrete crushing at the toe), the post-tensioning (force sized for recentering with margin — the wall must return, not just rock), the energy dissipators (sized for the damping target, detailed for replacement), and the capacity protection of everything else (the wall's forces go somewhere — foundations and diaphragms designed for the rocking demands). ACI's rocking-wall provisions (ACI 318-19 Chapter 18, ITG 5.1/5.2) and the PRESSS research program underpin the design.
Applications
Precast concrete buildings (the PRESSS system's origin — parking structures, warehouses, offices), mass-timber towers (rocking CLT walls — the damage-free timber seismic system), and bridges (rocking piers). The economic case: the building is occupiable immediately after the design earthquake — no plastic-hinge repair, no demolition. For owners who cannot tolerate downtime, rocking is the structural answer.
The bottom line
Rocking walls uplift and recenter in earthquakes via post-tensioning — damage-free seismic performance. Design the armored base, recentering tendons, and replaceable dissipaters per ACI ITG 5.1/5.2.
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