Spring-supported turbine table
The machine deck carried on spring units, so the vibration stays with the machine instead of travelling into the building.
Last updated 2026-09-07
What is Spring-supported turbine table?
A spring-supported turbine table separates the deck that carries the machine from the structure below it. The columns rise from the pile cap in the normal way, but instead of the deck being cast monolithically onto them it sits on spring units, commonly with damping elements built in. The machine and its deck become a mass on a soft support, and the vibration that the rotating shaft generates is largely kept within that mass rather than being passed down into the columns, the piles and the ground. Everything below the springs then has a much easier life, and so does everything around it.
Two things usually drive the choice. The first is what sits nearby: neighbouring structures, sensitive equipment, control rooms, and in some settings occupied buildings or transport infrastructure beyond the site boundary. Isolating the machine keeps the energy where it belongs. The second is space. Because the deck is a separate mass, the volume beneath it can be used far more freely for condensers, pipework, pumps, cabling and access, which on a tight layout can be worth more than the isolation itself. The turbine supplier sets the requirement for how the machine is to be supported and the designer, working with the spring unit supplier, produces an arrangement that meets it.
The cost is complexity. A spring-supported table is a more sensitive construction than a solid block in almost every respect. The deck has to be built on temporary supports and then transferred onto the springs in a controlled sequence. The springs need to be adjustable, accessible and maintainable for the life of the plant. The deck will move slightly, so every service, pipe and cable crossing the boundary needs a flexible connection, and every gap needs to stay a gap - a single hard contact anywhere across that boundary short-circuits the isolation and undoes the whole idea. Sites that build these successfully treat the transfer and the isolation gap survey as major hold points rather than routine steps.
How does Spring-supported turbine table work, step by step?
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Step 1: Establish the case for isolation early
The decision to isolate is taken at concept stage, because it changes the layout, the structure and the procurement. The drivers are assessed together: what the turbine supplier requires, what the surrounding structures and equipment can tolerate, what the neighbours and the site boundary demand, and how much of the space under the machine the layout needs to use. Isolation is not a late substitution for a solid block - the two are different structures with different piles, different columns and different construction sequences.
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Step 2: Design the table with the spring supplier in the room
The spring units are a designed component, not a bought item dropped in at the end. Their number, position, capacity, adjustment range and access arrangements are developed jointly by the structural designer, the spring unit supplier and the turbine supplier. The deck is designed as a stiff mass that spans between them, and the columns below are designed for the loads that arrive through them. Provision for future adjustment, for replacement and for inspection is designed in from the start, because the plant will run for decades and the units have to be reachable.
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Step 3: Build the piles, pile cap and columns
Below the springs the work is conventional heavy civils. Piles are installed and tested, the cap is cast, and the columns rise to the level where the spring units will sit. Accuracy at the top of the columns matters because the spring pedestals have to be level and correctly positioned. Bearing plinths are usually formed and finished carefully, with recesses or plates set to the spring supplier's requirements, and surveyed before anything is placed on them.
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Step 4: Set the spring units and their pedestals
Spring units are set on the prepared pedestals to the layout drawing, with their locking arrangement engaged so that they behave as rigid supports during construction. Each unit is identified, its position recorded and its condition checked. They are then protected, because a spring unit filled with grout washings or damaged by a dropped bar is a unit that has to come out again after the deck is on top of it.
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Step 5: Cast the deck on temporary supports
The deck is built on falsework or on temporary packs so that its weight goes into the columns rather than into the springs while it cures. It is a substantial reinforced concrete slab and beam structure, with the same congestion and the same embedded item discipline as a solid block. Setting-out is again taken from the independent survey control network, and the machine centreline is the datum. The deck is cured fully before any thought is given to transferring it.
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Step 6: Transfer the load onto the springs in a controlled sequence
Transfer is the defining operation. The locking arrangements are released and the temporary supports removed in the sequence the spring supplier specifies, so that load moves onto the units progressively and evenly rather than in one drop. Levels are monitored throughout and the units are adjusted as the deck takes up its final position. It is a supervised, staged operation with the spring supplier present on most projects, and it is treated as a hold point with its own method statement and its own records.
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Step 7: Establish and prove the isolation gap
Once the deck is floating, everything that crosses between the deck and the surrounding structure has to do so without touching. Pipework, cable containment, ducts, drainage, walkways, stairs and access platforms all need flexible connections or designed clearances. The gap is then surveyed all the way round and along every service crossing, and it is surveyed again before commissioning and after each major trade has finished. Grout runs, dropped materials, temporary props, scaffold ties and last-minute brackets are the usual culprits, and any one of them defeats the isolation.
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Step 8: Hand over with the adjustment and maintenance regime in place
The final records cover the position and setting of every spring unit, the surveyed level of the deck, the as-built survey of the embedded items against the turbine supplier's tolerances, and the confirmed isolation gap. The operator is given the arrangement for inspecting, adjusting and replacing the units, and access to them is confirmed as clear. Long-term monitoring of the deck level is common, because a machine on springs is a system that is expected to be checked rather than forgotten.
What are the benefits of Spring-supported turbine table?
- Keeps machine vibration within the isolated mass instead of passing it into the structure and the ground
- Protects surrounding buildings, sensitive equipment and neighbours beyond the site boundary
- Frees the volume beneath the deck for condensers, pipework, pumps, cabling and access
- Reduces the demands on the columns, piles and ground below the springs
- Spring units can be adjusted over the life of the plant to correct level and take up long-term movement
- Suits congested or urban layouts where a solid block would sterilise too much space
What are the limitations of Spring-supported turbine table?
- Substantially more complex and more expensive than a solid block
- Adds a supervised load transfer operation that is a genuine risk point in the programme
- Every service crossing the boundary needs a flexible connection, which multiplies interfaces
- A single hard contact anywhere across the gap defeats the isolation and can be hard to find
- Spring units must stay accessible for inspection, adjustment and replacement for the life of the plant
- Depends on close coordination between the turbine supplier, the spring supplier and the designer throughout
What is Spring-supported turbine table best suited for?
What plant does Spring-supported turbine table need?
- Piling rig and testing equipment for the foundations below the columns
- Crawler cranes for deck reinforcement, formwork and spring unit placement
- Heavy falsework and temporary support systems designed for the deck and for controlled release
- Spring units and their locking, jacking and adjustment equipment supplied with the package
- Precision levelling and monitoring equipment for the transfer operation
- Survey equipment and feeler gauges for the isolation gap inspection regime
How is Spring-supported turbine table quality-checked?
- Isolation requirement confirmed with the turbine supplier and the spring supplier before design freeze
- Column tops and spring pedestals surveyed for level and position before units are placed
- Each spring unit identified, positioned, locked and protected, with records kept
- Load transfer carried out as a hold point to an agreed method statement, with monitored levels at every stage
- Isolation gap surveyed after transfer, after each major trade and again before commissioning
- As-built survey of embedded items against the turbine supplier's tolerances, plus a handover record of spring settings and access