Jacking: Incremental Lowering
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A complex frame of structural steelwork was constructed from the basement slab with a series of locking collar hydraulic jacks incorporated to ensure a positive load transfer and allow for incremental lowering. The frame was loaded to 75% of the structural dead load prior to the existing ground floor slab being severed. The section of slab directly beneath the sculpture remained untouched, with additional kentledge being added to ensure no risk of overturning due to high wind loadings. Further lateral bracing was installed to the retained base slab using adjustable raking shores. Once the saw cutting was complete, the sculpture sat entirely on the temporary frames.

Using a sequence of 12 hydraulic jacks controlled at a central point, the structure was incrementally lowered in 50 mm tranches until the required revised level was achieved, with the raking shores being adjusted as the lowering progressed. The jacking works took place on consecutive night shifts to ensure no disruption to commuters. On completion, the sculpture was locked in position and the steel support grillage was incorporated into the new permanent works. All works were completed successfully on time and budget.

Find out more about this complex task here.