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Slip forming, continuous poured, continuously formed, or slipform construction is a construction method in which concrete is placed into a form that may be in continuous motion horizontally, or incrementally raised vertically.
In horizontal construction, such as roadways and curbs, the weight of the concrete, forms, and any associated machinery is borne by the ground. In vertical construction, such as bridges, towers, buildings, and dams, forms are raised hydraulically in increments, no faster than the most recently poured concrete can set and support the combined weight of the concrete, forms, and machinery, and the pressure of concrete consolidation.Nawy, Concrete Construction Engineering Handbook, 2008, p. 10—33.
Slipforming enables continuous, non-interrupted, cast-in-place, cold joint- and seam-free concrete structures that have performance characteristics superior to those of piecewise construction using discrete form elements.
In 1910, MacDonald published a paper "Moving Forms for Reinforced Concrete Storage Bins," James MacDonald - "Moving Forms for Reinforced Concrete Storage Bins." Proceedings of the Seventh Annual Convention Held at N.Y., N.Y. Volume 7, By National Association of Cement Users (U.S.). December 12–20, 1910. page 554.[2] describing the use of molds for moving forms, using jacks and concrete to form a continuous structure without joints or seams. This paper details the concept and procedure for creating slip form concrete structures. On May 24, 1917, a patent was issued to James MacDonald of Chicago, "for a device to move and elevate a concrete form in a vertical plane".Official gazette of the United States Patent Office, By United States. Patent Office Volume CCXXXVII. April 24, 1917, page 943.
The former Landmark Hotel & Casino in Las Vegas was constructed in 1961 by MacDonald Engineering as a subcontractor, utilizing Macdonald’s concept of slip form concrete construction to build the 31 story reinforced steel tower. Construction of tower for the LandMark Hotel/Casino, Las Vegas
Residential and commercial building also was introduced in the late 1960s in USA."'Slip Forming' Technique Introduced in Baltimore." Washington Post. May 1, 1971. One of Its first uses in high-rise buildings in the United States was on the shear wall supported apartment building at Turk & Eddy Streets in San Francisco, CA, in 1962, built by the San Francisco office of Macdonald Engineering. The first notable use of the method in a residential/retail business was the Skylon Tower in Niagara Falls, Ontario, which was completed in 1965. Another unusual structure was the tapered buttress structures for the Sheraton Waikiki Hotel in Honolulu, Hawaii, in 1969. Another shear wall supported structure was the Casa Del Mar Condominium on Key Biscayne, Miami, FL in 1970.
From the 1950s, the vertical technique was adapted to mining head frames, ventilation structures, below grade shaft lining, and coal train loading silos; theme and communication tower construction; high rise office building cores; shear wall supported apartment buildings; tapered stacks and intake tower, etc. It is used for structures which would otherwise not be possible, such as the separate legs of the Troll A deep sea oil drilling platform which stands on the sea floor in water about deep, has an overall height of weighs , and has the distinction of being the tallest structure ever moved (Towing) by mankind.
In addition to the typical silos and shear walls and cores in buildings, the system is used for lining underground shafts and surge tanks in hydroelectric generating facilities. The technique was utilized to build the Inco Superstack in Greater Sudbury, Ontario, and the CN Tower in Toronto. In 2010, the technique was used to build the core of the supertall Shard London Bridge tower in London, England.
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