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Slip Form

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Construction Processes

Slip form construction is a method of continuously pouring concrete into a form or mold that moves up vertically with the assistance of hydraulic or screw jacks.

[edit] History

Slip form construction was first used in the 1930s in the building and erection of grain-storage silos and other similar structures. Early slip forming techniques relied on hydraulic jacks and the pouring of concrete into a form work made of timber.[1] Slip forming was also used to eventually build lighthouse towers.[2] Today, slip forming is used to build everything from silo complexes, chimneys, reservoirs, medium- to high-rise housing developments, to office buildings, hotels, hospitals, bridge support piers, in-ground shafts to dams and power stations.[3] It is also still used to build elevator cores and batch houses.[4]

One of the more notable structures constructed using a slip form in the last century was the CN Tower in Toronto, Canada built in 1973.[5]

Slip forming has even been adapted in the paving of roadways, bicycle paths, and traffic barriers with the introduction of slip form paving equipment.[6] Slip form paving was also implemented in the paving of airport aprons, taxiways, and runways starting in the mid 1990s in the U.K.[7]

[edit] Process

As the structure rises, the section of previously poured concrete hardens and forms a kind of support wall that is strong enough to withstand the concrete poured over top of it.[8] Pouring continues until the desired height of the structure is reached, allowing for a type of monolithic poured concrete structure that is positioned on top of a foundation and completely hollow inside.

The hydraulic jacks are spaced at equal intervals to lift the form upwards in gradual increments of about one inch (2.5 cm) every five to ten minutes, depending on what the required sliding speed is. The standard sliding rate in slip form construction is usually nine inches (23 cm) per hour.[9] The unique aspect of slip forming is how durable the poured concrete becomes within two to four hours of being poured. The concrete is strong enough to actually stand safely and completely unsupported.[10]

[edit] References

  1. Fabquip Slipform. Fabquip Construction Systems, 2008-09-29.
  2. New Slip Form method for lighthouse construction. Project Monitor, 2008-09-29.
  3. Fabquip Slipform. Fabquip Construction Systems, 2008-09-29.
  4. Slipform Concrete Silos. Marietta Silos, 2008-09-29.
  5. CN Tower History. CNTower.com, 2008-09-29.
  6. Paving the Way to Outstading Product Quality and Superior Customer Service. PowerPavers.com, 2008-09-29.
  7. The Slip-Form Technique. BritPave.org.uk, 2008-09-29.
  8. Slip Form. Answers.com, 2008-09-29.
  9. New Slip Form method for lighthouse construction. Project Monitor, 2008-09-29.
  10. Fabquip Slipform. Fabquip Construction Systems, 2008-09-29.