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Slip forming
Slip forming
Slip forming
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The first residential building of slipform construction; erected in 1950 in Västertorp, Sweden, by AB Bygging
Later picture of the residential building in Västertorp

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.[1]

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.[citation needed]

Overview

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Slip forming relies on the quick-setting properties of concrete, and requires a balance between workability and quick-setting capacity. Concrete needs to be workable enough to be placed into the form and consolidated (via vibration), yet quick-setting enough to emerge from the form with strength. This strength is needed because the freshly set concrete must not only permit the form to "slip" by the concrete without disturbing it, but also support the pressure of the new concrete and resist collapse caused by the vibration of the compaction machinery.

Slipforming of a 118 metre-tall grain silo in Zürich in 2015
Continuous slip formed gravity-based structure supports under construction in a Norwegian fjord. The visible jib cranes would be delivering buckets of concrete to the support cylinders during the continuous pour of concrete creating seamless walls.

Horizontal

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In horizontal slip forming for pavement, curbs, and traffic separation walls, concrete is laid down, vibrated, worked, and settled in place while the form itself slowly moves ahead. This method was initially devised and utilized in Interstate Highway construction initiated by the Eisenhower administration during the 1950s.

Slipform monobox system

Vertical

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In vertical slip forming the concrete form may be surrounded by a platform on which workers stand, placing steel reinforcing rods ahead of the concrete and ensuring a smooth pour.[2] Together, the concrete form and working platform are raised by means of hydraulic jacks.[3] The slipform can only rise at a rate which permits the concrete to harden by the time it emerges from the bottom of the form.[1]

History

[edit]

The slip forming technique was in use by the early 20th century for building silos and grain elevators. James MacDonald, of MacDonald Engineering of Chicago was the pioneer in utilizing slip form concrete for construction. His concept of placing circular bins in clusters was patented, with photographs and illustrations, contained in a 1907 book, "The Design Of Walls, Bins, And Grain Elevators".[4]

In 1910, MacDonald published a paper "Moving Forms for Reinforced Concrete Storage Bins," [5] 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".[6]

Silos

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James MacDonald’s bin and silo design was utilized around the world into the late 1970s by MacDonald Engineering. In the 1947-1950 period, MacDonald Engineering constructed over 40 concrete towers using the slip-form method for AT&T Long Lines[7] up to 58 m (190 ft) tall for microwave relay stations across the United States.

AT&T Long Lines relay tower in Indiana constructed with the slip-form method
Two coal silos being constructed by slip forming

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 steel-reinforced tower.[8]

Residential and commercial building

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The technique was introduced to residential and commercial buildings already in the 1950s in Sweden. The Swedish company Bygging developed in 1944 the first hydraulic hijacks to lift the forms, which got patented. The first houses were built in Västertorp, Sweden, and Bygging became pioneers around the world with slip forming technique, from 1980 with the name Bygging-Uddemann. [9]

Residential and commercial building also was introduced in the late 1960s in USA.[2] 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.[citation needed] 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.[citation needed] 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 hydro intake structures, 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 300 m (980 ft) deep, has an overall height of 472 m (1,549 ft) weighs 595,000 t (656,000 short tons), and has the distinction of being the tallest structure ever moved (towed) 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 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.

References

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Bibliography

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Slip forming

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from Grokipedia
Slip forming, also known as slipform , is a technique in which is continuously poured into a moving that is incrementally raised, enabling the seamless and rapid erection of vertical structures such as silos, towers, chimneys, and building cores. This method eliminates the need for repetitive assembly and disassembly associated with traditional casting, allowing the structure to grow monolithically without horizontal construction joints, typically at rates of 300-450 mm per hour. The origins of slip forming trace back to the late , with early applications in for horizontal concrete rafts and the first vertical use in 1899 for a in by the Peavey Elevator Company. Technological advancements, including screw jacks in 1903, pneumatic systems in the , and hydraulic jacks by the , significantly improved efficiency, enabling slide rates to exceed 40 inches per hour by the 1970s and expanding its use to diverse structures like high-rise cores and nuclear containment walls. Primarily employed for vertical , the technique can also adapt to horizontal or tapered forms for applications such as and cooling towers, where adjusts for varying dimensions. In the slip forming process, —typically composed of panels, yokes, frames, hydraulic jacks, and jack rods—is self-supported on the emerging and lifted continuously as is placed in 200-250 mm layers and vibrated for compaction. Platforms integrated into the system facilitate working (for placement), finishing (for surface treatment), and storage (for materials), minimizing reliance on cranes and ensuring worker safety through guardrails and enclosed areas. The mix, with a slump of 75-100 mm, must achieve initial set within 2-3 hours to support the load, requiring precise monitoring of environmental conditions and admixtures. Key advantages of slip forming include substantial cost savings in time and expenses—due to reusable components, reduced labor for joint sealing, and the ability to install services like early in the process. It is particularly suited for structures over four storeys with regular cross-sections, such as water tanks, piers, and high-rise lift shafts, where verticality is maintained through experienced and can reach heights of 275 m or more. Despite its efficiency, the method demands skilled personnel and meticulous planning to manage challenges like setting rates and structural stability during lifting.

Fundamentals

Definition and Process

Slip forming is a construction technique in which is continuously poured into moving to produce monolithic structures, differing from traditional methods that employ stationary for discrete pours. This process enables the creation of seamless, joint-free elements with uniform strength and enhanced durability, as the eliminates the need for construction joints that can introduce weaknesses. The basic process begins with the preparation of foundations and initial wall starters to support the assembly. Plastic is then placed continuously into the in layers typically 100-250 mm thick, where it is compacted through to ensure proper consolidation. As the begins to set, the is advanced—either lifted vertically or moved horizontally—at a controlled rate that aligns with the material's hardening, allowing the exposed below or behind the form to cure progressively without additional support. The rate of form movement, typically 0.1-0.45 meters per hour for vertical applications, is determined by the concrete's setting time and early-age strength gain, ensuring the material achieves sufficient —generally 1-3.5 MPa—before the form exposes it to full loading. This controlled pace prevents deformation and maintains structural integrity throughout the pour. Slip forming variants include vertical and horizontal configurations, adapted to the project's orientation.

Components and Equipment

Slip forming relies on a suite of specialized components and equipment designed to facilitate the continuous placement and elevation of while maintaining structural integrity and precision. The core elements include panels, yokes or walers for support, and lifting mechanisms such as hydraulic jacks or climbing screws. These components work in tandem to create a self-supporting system that rises incrementally, typically at rates of 300 mm per hour, allowing for the formation of monolithic structures without interruption. Formwork panels, often referred to as sheathing, form the primary enclosure for the fresh and are constructed from durable materials like high-strength or lightweight aluminum to ensure watertightness and resistance to hydrostatic . These panels are typically 1 to 2 meters in and feature adjustable widths to accommodate varying structural geometries, with tight joints and smooth surfaces coated to prevent concrete adhesion and reduce friction during lifting. panels provide rigidity for high-load applications, while aluminum variants offer easier handling and resistance through anodized or coatings, promoting longevity and reusability across multiple projects. Yokes and walers serve as the structural backbone, distributing loads and preventing formwork deformation under the lateral pressure of plastic . Yokes, typically inverted U-shaped frames, are spaced approximately 2 meters apart and connect to walers—horizontal or aluminum beams that stiffen the panels and transmit lifting forces evenly. This modular arrangement allows for quick assembly and disassembly, with yokes designed to integrate seamlessly with lifting systems while providing clearance for installation. Lifting is achieved through hydraulic jacks or mechanical climbing screws mounted on vertical jackrods, enabling synchronized upward movement of the entire assembly. Hydraulic jacks, with capacities ranging from 3 to 25 tons, grip the jackrods—1-inch diameter bars—and advance the forms at controlled speeds of 150 to 1,000 per hour, ensuring uniform elevation across the structure. Climbing screws, an alternative for smaller-scale operations, use motorized rotation for precise increments, often preferred in regions with variable power supplies. These systems incorporate load sensors and position encoders to maintain alignment tolerances, such as ±3 verticality over panel heights. Auxiliary equipment supports the concrete placement and finishing processes, including distribution systems like pumps, chutes, and augers that deliver in shallow 150- to 250-mm lifts directly to the forms. Immersion vibrators, typically spud-type with electronic controls, consolidate the mix to eliminate voids and ensure bonding between lifts, operating in 150- to 250-mm increments. Multi-level working platforms, constructed from or aluminum with a minimum live load capacity of 3.6 kN/m², provide safe access for laborers: an upper deck for material storage, a middle deck for placement and , and a lower deck for finishing. features, such as edge rails, guardrails, and shields, are integrated into platforms and yokes to comply with occupational standards and prevent falls or debris hazards. Design considerations emphasize for high reusability—often exceeding 100 cycles per set—and precise to achieve alignment tolerances of ±3 mm vertically and horizontally, monitored via or GPS systems. Components are fabricated with high-strength (yield strength ≥ 250 MPa) or aluminum alloys for , with coatings like release agents to minimize and facilitate smooth operation. Integration of lifting systems with yokes ensures balanced load distribution, while overall rigidity counters pressures calculated per established standards, prioritizing safety and efficiency in continuous .

Types

Vertical Slip Forming

Vertical slip forming employs hydraulic jacks mounted on vertical rods embedded in the to incrementally elevate the as the freshly placed gains sufficient strength below, facilitating the continuous extrusion of tall, uniform structures such as and towers. This process differs from horizontal methods by focusing on upward progression, where the forms are lifted in small increments, typically synchronized across multiple jacks to maintain plumb alignment and even pressure distribution. The vertical lifting rate typically ranges from 2 to 7 meters per day, depending on the structure's design and environmental conditions, with the pace strictly controlled by the concrete's development to ensure structural integrity. Strength gain is assessed using methods like the maturity approach, which accounts for effects on curing to predict when the below the forms has reached the required load-bearing capacity, typically around 0.2 MPa (30 psi) for safe . The lift height per cycle can be approximated by the h=v×th = v \times t, where hh is the lift height, vv is the jacking speed, and tt is the concrete setting time; for instance, with a form depth of 1.2 meters and a 2-3 hour setting time, speeds of 0.4-0.6 meters per hour are achievable. Adaptations for vertical slip forming include inclined form panels to accommodate tapered profiles, as seen in where the forms adjust angularly to follow the structure's reducing , ensuring a smooth, continuous pour without interruptions. For high-rise buildings, internal climbing forms equipped with hydraulic jacks are used to erect core walls independently within the structure, allowing placement and pouring at elevated heights while minimizing reliance on external cranes. Safety protocols emphasize continuous load monitoring on hydraulic jacks and supports to detect imbalances or overloads that could lead to form failure, with requirements for daily inspections and strain gauges to verify even distribution across all jacking points. Wind resistance is addressed through form designs that incorporate bracing and guy wires capable of withstanding site-specific gusts up to 90 km/h, alongside operational halts during high winds to prevent lateral sway or tipping.

Horizontal Slip Forming

Horizontal slip forming is a construction technique employed for creating linear, ground-level concrete structures such as pavements, channels, and barriers by continuously advancing formwork along a horizontal path while depositing and curing concrete. Unlike vertical methods, it focuses on progression in length or width rather than height, utilizing self-propelled machines that extrude concrete in situ without relying on stationary forms. The mechanism involves mounting rigid forms on rails, tracks, or wheels, where the assembly is propelled forward by winches, hydraulic jacks, or tracked undercarriages at a controlled rate, allowing the concrete poured into the forms to set and gain sufficient strength behind the moving mold. Concrete, typically a stiff low-slump mix (20-80 mm slump), is fed via hoppers, consolidated by internal vibrators (operating at 7,000–9,000 vibrations per minute), and shaped by the forms as the machine advances, producing a seamless, monolithic section. This process ensures the concrete becomes self-supporting shortly after extrusion, with the forms maintaining precise dimensions throughout. Operational speed and control are tailored to the concrete's curing rate, slab thickness, and mix design, typically ranging from 1 to 2.5 meters per minute (60-150 meters per hour) for pavements, though slower rates of 9-20 meters per hour apply to thicker sections like or barriers to ensure adequate compaction and strength gain. Advance rates are monitored and adjusted using automated controls to prevent defects, with the machine following guide wires or digital systems for straight-line progression. For specialized applications, such as curved alignments in tunnels or ramps, forms are articulated with adjustable segments to follow radii as small as 10 meters, maintaining uniformity. Slipform pavers, a common adaptation for , integrate finishing tools like oscillating screeds or tamper bars (0-150 strokes per minute) and profile pans to strike off excess material, consolidate, and impart a textured surface in a single pass. Precision is critical for achieving even surfaces and structural , relying on leveling sensors, laser-guided systems, or GPS for real-time adjustments to grade, alignment, and cross-slope, often maintaining tolerances within 3-6 mm over extended lengths. Joint treatments, such as saw cuts applied 6-30 hours after placement, ensure continuity and control cracking in longer sections, while side forms prevent seepage and maintain edge sharpness. These elements collectively enable high-accuracy construction with minimal post-processing.

Applications

Storage Structures and Silos

Slip forming is particularly well-suited for the construction of storage structures and silos, such as grain silos, water tanks, and nuclear containment vessels, due to its ability to produce seamless, cylindrical walls that leverage rotational symmetry for uniform stress distribution and minimal joints, enhancing containment integrity and watertightness. This method excels in creating monolithic structures where hoop stresses from internal pressures demand continuous reinforcement without construction interruptions that could introduce vulnerabilities. In the slip forming process for these structures, rotating hydraulic jacks lift the incrementally—typically 2.5 cm every 5-15 minutes—while is poured continuously in thin layers, allowing simultaneous placement and curing to achieve even wall thicknesses of 0.2-0.4 meters. Embedded reinforcements, including hoop bars, are installed progressively to counter circumferential tensile forces, with insert forms dropped in to thicken walls as needed for larger diameters or higher loads. This adaptation ensures a smooth, joint-free finish and supports 24-hour operations, often advancing 2-3 meters per day. Notable early examples include the Peavey-Haglin Experimental Grain Elevator in , built in 1899-1900 as the first U.S. grain storage using slip forms raised by jacks on vertical rods, pioneering the technique for cylindrical bins. In modern applications, slip forming has been employed for LNG storage tanks, such as the full-containment tank at Isle of , , featuring a 92.4-meter diameter outer shell poured continuously to 50.4 meters high. These projects demonstrate the method's scalability, accommodating diameters up to 100 meters and heights reaching 50 meters in single, uninterrupted pours, as seen in LNG facilities with strict tolerances for insulation and thermal performance. For nuclear containments, slip forming has constructed heavily reinforced cylindrical shield walls, like those at the Satsop Nuclear Plant, where the process handled dense congestion while maintaining structural uniformity.

Buildings and Towers

Slip forming is extensively applied in the construction of high-rise buildings and towers, particularly for creating core walls, elevator shafts, and chimneys in . This vertical technique enables the continuous pouring of sections, forming seamless, joint-free structures that provide and house critical building services such as lifts, , and ventilation systems. In medium-height buildings, up to around 30 meters or ten stories, slip forming can encompass the entire core or even full-building pours for simpler geometries, allowing for rapid vertical progression without repeated form stripping. For chimneys integrated into tall structures, the method supports tapered or cylindrical forms, ensuring monolithic construction that withstands and loads. Adaptations in slip forming for buildings and towers include multi-form setups, where multiple independent units operate simultaneously to lift different sections of the core, such as separate shafts or walls, optimizing workflow and reducing overall construction time. These systems often integrate with tower cranes for efficient material delivery, positioning aggregates, , and pumps directly above the forms to maintain continuous pouring rates of 4-8 meters per day. This vertical slip forming process, reliant on hydraulic jacks climbing along embedded rods, minimizes labor and enhances safety by enclosing the work area within the moving platform. Notable examples illustrate its impact in tall structures. The in , completed in 1976 at 553 meters, utilized slip forming to pour its tapered shaft continuously over several months, achieving a seamless exterior that supported the antenna mast. In the 2000s, the in employed a specialized slipform variant—known as jumpform—for its central core, enabling the 828-meter tower's rapid ascent by allowing two to three levels per day with high-performance . More recently, in 2020, a 121-meter (398-foot) test tower in , Georgia, USA was constructed using slip forming, completing the core in 56 days through precise coordination of forms and materials. Modern trends in slip forming for buildings and towers emphasize and efficiency, incorporating low-carbon mixes to reduce embodied emissions while maintaining structural integrity. Post-2020 projects increasingly adopt hybrid methods, blending slip-formed cores with precast floor slabs and facades to accelerate urban , reduce site waste, and adapt to dense city environments.

Infrastructure Projects

Slip forming is extensively applied in transportation and utility infrastructure for constructing linear elements such as bridge piers and abutments, tunnel floors and linings, canal linings, and airport runway pavements, as well as curbs and safety barriers using specialized slipform pavers. These applications leverage the continuous pouring process to create long, uniform concrete sections efficiently over extended distances. Key adaptations for infrastructure include mobile slipform pavers equipped with hydraulic systems that advance continuously along the project alignment, enabling construction over long spans without repeated form setup. Outdoor pours, common in these projects, incorporate weatherproof enclosures or rapid-setting concrete mixes to protect against environmental factors like rain or temperature fluctuations. Notable examples include the widespread adoption of slipform pavers during the U.S. in the 1950s, with early prototypes developed at and by the Iowa State Highway Commission starting in the late . In the 1990s, slip forming was used for the Rail Link project to construct tunnel floors and evacuation walkways, reducing on-site labor through continuous operation. More recently, post-2020 high-speed rail projects in have employed slip forming for parapets and approach structures to meet tight timelines. This technique achieves significant labor reductions compared to traditional fixed-form methods—for linear infrastructure per kilometer, primarily by minimizing formwork handling and enabling fewer workers per shift.

Historical Development

Early Innovations

The origins of slip forming trace back to the late 19th century. The first recorded use was in 1885 by Carrico in Texas to build a small horizontal concrete raft. The first vertical application occurred in 1899, when the Peavey Elevator Company in St. Louis Park, Minnesota, experimented with the technique for a grain elevator, using steel angle walers, yokes, and hand-operated locomotive screw jacks to raise wooden forms incrementally. This resulted in the world's first cylindrical reinforced concrete grain silo, the Peavey-Haglin Experimental Concrete Grain Elevator, completed in 1900 and capable of holding 25,000 bushels. Engineer Milo S. Ketchum documented related techniques, including moving forms for reinforced concrete grain elevators, in his 1907 publication The Design of Walls, Bins, and Grain Elevators, emphasizing structural integrity under load. Building on these ideas, James MacDonald of MacDonald Engineering in Chicago pioneered further practical implementation, securing a U.S. patent on May 24, 1917, described as "a device to move and elevate a concrete form in a vertical plane," which detailed a mechanism for vertically sliding forms to enable continuous pouring for circular bins and silos. This patent marked a key innovation, shifting from labor-intensive repositioning of fixed forms to a dynamic system that reduced construction time for agricultural storage. The first practical applications emerged in the U.S. Midwest, where slip forming was employed for grain elevators and to meet growing agricultural demands. By the , the technique gained traction for farm construction in the Midwest, particularly in states like and , where farmers adopted it for durable, weather-resistant storage amid expanding and livestock operations; for instance, stave and slip-formed proliferated to preserve more effectively than wooden predecessors. These early uses demonstrated slip forming's efficiency in producing tall, uniform structures without joints, though initial implementations relied on manual jacks and faced limitations in speed and precision. Key advancements in the mid-20th century addressed these constraints, notably the introduction of hydraulic jacking systems in the 1940s by Swedish firms like Bygging Uddemann, whose experiments replaced mechanical screw jacks with synchronized hydraulic units connected to oil pumps, allowing smoother, faster lifts of up to 1 meter per hour and enabling taller structures with greater control. This innovation was pivotal for vertical applications, as seen in the 1950s construction of Long Lines microwave relay towers across the U.S., such as the 190-foot Type 4C tower in Collins, , built in early 1950 using slip forming to support antennas, marking one of the first non-agricultural vertical uses. Early slip forming also grappled with form stability challenges, as wooden sheathing prone to warping and deflection under wet loads risked misalignment; these were largely overcome by incorporating steel reinforcements and yokes into the design, providing rigidity and even pressure distribution during lifts, as refined in post-1910s patents and practices.

Expansion and Modern Use

Following the initial adoption in industrial structures, slip forming expanded significantly in the mid-20th century to residential and high-rise applications. In 1950, the first slip-formed residential building—a seven-story apartment block in Västertorp, Stockholm, Sweden—was completed, marking the technique's transition to multi-story housing and demonstrating its potential for efficient urban development. By the 1960s, slip forming was applied to taller commercial structures, such as the Landmark Hotel and Casino in Las Vegas, where construction of the 31-story tower began in 1961 using the method as a showcase for its efficiency in vertical construction. This period saw widespread use in North American high-rises, contributing to the technique's reputation for speed and precision in vertical construction. In the 2010s, slip forming supported iconic megastructures, including the core of in , completed in 2012, where it facilitated the placement of 12,000 cubic meters of concrete at a rate of three meters per day, enabling the building to reach its 310-meter height efficiently. Post-2020 advancements have integrated and sensors to enhance accuracy and safety; for instance, IoT sensors embedded in slip forms monitor vertical alignment and rotational deviations in real-time, allowing closed-loop adjustments during pours to minimize errors in high-precision projects. Sustainable concrete mixes, incorporating recycled aggregates and low-carbon cements, have been adapted for slip forming in eco-friendly builds, reducing emissions while maintaining structural integrity, as explored in robotic slip-form casting techniques for facade elements. Additionally, the method has been employed in disaster-resilient designs, such as low-cost soil-cement walls in seismic zones, where slip forms create seamless, joint-free structures that better withstand lateral forces. The technique's global adoption has surged in and for large-scale megaprojects, driven by and demands. In , slip forming remains integral to cores, as seen in ongoing high-rise developments, while in , particularly , innovative slip applications have accelerated construction of supertall buildings, shortening timelines by up to 30% through continuous pouring. Integration with (BIM) software has further optimized these efforts, enabling of slip form systems for tapered structures and real-time of construction sequences to predict and mitigate issues. Recent post-2020 projects highlight slip forming's versatility in emerging sectors. For offshore wind installations, the ECO TLP floating platform, under development since 2023, utilizes slip-formed cylindrical hulls for stable foundations, supporting deployment in deep waters and advancing infrastructure. In , slip forming has been key to the construction of massive caissons for Singapore's expansion, weighing 13,000 tonnes each, which indirectly supports logistics for green energy projects including components.

Advantages and Challenges

Benefits

Slip forming offers significant efficiency gains over traditional methods by enabling continuous placement without the need for repeated assembly and disassembly of forms. This process allows for vertical lifts of 3 to 5 meters per 24-hour period in vertical applications, effectively doubling the construction speed compared to fixed-form techniques. As a result, overall cycle times can be reduced by up to 50%, minimizing downtime and accelerating project completion. Additionally, the method requires fewer workers—typically 24 to 60 for cores, averaging around 43—compared to the larger crews needed for conventional forming, thereby optimizing labor utilization. The quality of structures produced by slip forming is enhanced due to the creation of monolithic concrete elements without horizontal cold joints, which eliminates potential weak points and improves overall durability and watertightness. This joint-free construction also contributes to superior surface finishes and geometrical accuracy, with deviations often limited to less than 5 mm for structures under 3 meters in height. In advanced applications, such as marine structures, slip forming can yield up to a 20% increase in in-situ concrete strength relative to conventional methods, further bolstering long-term performance. Economically, slip forming reduces costs through the of forms, which lowers material expenses by eliminating the need for extensive fixed , and shortens project timelines that in turn decrease financing and overhead burdens. These efficiencies can lead to overall cost savings in suitable projects, particularly for tall or repetitive structures where labor and form-related expenditures are minimized. The technique's streamlined process also cuts down on patching and repair needs, providing additional financial benefits. Slip forming demonstrates versatility in accommodating complex geometries and a range of structure types, from and towers to horizontal pavements, without requiring extensive modifications to the system. For enclosed construction sites, the method is largely weather-independent, as ongoing operations protect the work area, ensuring consistent progress regardless of external conditions. This adaptability makes it ideal for projects demanding precision in curved or irregular shapes, where traditional methods would be more cumbersome.

Limitations and Considerations

Slip forming, while efficient for certain vertical structures, has notable limitations in its applicability and execution. It is primarily suited for monolithic, uniformly shaped elements such as cylindrical , chimneys, and building cores, but cannot simultaneously cast horizontal components like beams, slabs, or corbels, which must be added post-construction. Complex geometries, embedded items, or frequent openings can interrupt the continuous process, necessitating supplemental staging or bracing that complicates the operation and increases costs. Additionally, the technique is less viable for tapered or irregular forms without specialized contractor expertise, limiting its use in non-uniform structures like certain chimneys. Operational challenges arise from the method's demand for uninterrupted workflows. delivery and placement must be continuous to avoid cold joints or surface defects, with any delays risking structural weaknesses; this requires precise coordination of materials, logistics, and labor, often extending to 24-hour operations regardless of weather. The advance rate, typically 150–300 per hour for vertical slips, is constrained by the 's setting time and form depth (usually 1.2–1.8 m), with faster rates risking or inadequate strength and slower rates in cold weather (e.g., 125 /hour at 10°C) prolonging the process. Form drag forces, which can reach 100 lb per linear foot, and hydrostatic pressures from fresh further demand robust , while cumulative alignment deviations over height require constant monitoring with tools like lasers to maintain tolerances (e.g., ±25 per 15 m). Safety considerations are paramount due to the elevated, dynamic work environment. Platforms must include guardrails at least 1.07 m high, personal systems with 22 kN tie-off capacity, and emergency stops, with daily inspections mandatory to mitigate risks from falls or hydraulic failures. Wind loads pose significant hazards on tall structures, often halting operations at sustained speeds over 40–50 km/h, and require temporary bracing and stations for stability. The irreversible nature of the slip—once initiated, corrections are impossible without major rework—amplifies risks from inexperience, such as form sticking or misalignment, underscoring the need for pre-planned designs and skilled supervision. Design and material considerations add further complexity. Reinforcement must allow for form movement, with clearances and splices designed to prevent congestion, while the concrete mix needs a balance of workability (slump 20–80 mm) and early strength (0.3–0.7 MPa in green state) to support self-weight, vibration, and equipment loads without defects like honeycombing or tearing. High initial costs for specialized jacks, yokes, and 24-hour support facilities, combined with the need for a familiarized labor force and on-site material management, make it less economical for smaller projects. Weather extremes, such as cold requiring heated mixes or hot conditions accelerating setting, demand adaptive strategies, including multiple mix designs and slower rates, to ensure quality. Overall, these factors highlight the importance of thorough site planning and expertise to mitigate potential defects and ensure structural integrity.

References

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  24. https://www.idc-online.com/technical_references/pdfs/civil_engineering/Slipform_Construction_of_High_Rise_Building_Cores.pdf
  25. https://www.concrete.org.uk/fingertips/vertical-slipform-systems/
  26. https://www.doka.com/uk/news/slipform_vs_jumpform
  27. https://www.gleitbau.com/en/products/slipforming/conical
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  29. https://www.enr.com/articles/49267-slipforming-next-level-coordination-speed-erection-of-398-ft-tall-elevator-test-tower
  30. https://www.cntower.ca/history
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  32. https://www.concretecentre.com/News/2020/Design-of-tall-buildings.aspx
  33. https://global.ctbuh.org/resources/papers/download/1702-high-rise-buildings-in-the-netherlands-hybrid-structures-and-precast-concrete.pdf
  34. https://bygging-uddemann.com/our-services/slipform-solutions/traditional-slipform/
  35. https://www.gomaco.com/resources/canal_slope.html
  36. https://www.ajbuildscaffold.com/what-is-slip-formwork
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  41. https://eliteroads.com.au/blog/slip-form-paving-revolutionising-road-construction
  42. https://www.atlasobscura.com/places/nordic-ware-smokestack-peaveys-folly
  43. https://www.3dcpnewswire.com/p/history-of-3d-concrete-printing
  44. https://idnc.library.illinois.edu/?a=d&d=PFR19220128.2.4
  45. https://bygging-uddemann.com/cool_timeline/invention-of-the-hydraulic-slipform-jack/
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  48. https://flexcrete.com/fast-track-construction-revolutionary-slipformed-core/
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  53. https://www.scirp.org/journal/paperinformation?paperid=36176
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  55. https://starconcord.com.sg/assembly-line-concrete-bases-for-floating-offshore-wind-towers/
  56. https://apps.dtic.mil/sti/tr/pdf/ADA167786.pdf
  57. https://www.sciencedirect.com/science/article/pii/S2090447924005732
  58. http://www.abece.com.br/web/restrito/restrito/pdf/ch124.pdf
  59. https://www.doka.com/us/solutions/index
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  61. https://mastercivilengineer.com/slip-formwork-applications-advantages-and-disadvantages/
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