What Is Slip Formwork?
Slip formwork or slipform is a modern method of casting concrete that involves a dynamic or moving framework system. In this method, concrete is poured while the entire formwork keeps moving upwards steadily. The process stops only when the required casting length is completed.
The slip form method needs continuous monitoring of concrete pouring and its setting rate to ensure the forms are not being raised too fast. This advance technique also depends on the fast setting and cooling properties of concrete.
Slip formwork is the best technique that executes fast and rapid construction in unusual structures such as cooling towers, chimneys, silos, roadway, and bridge construction.
Although slip forming method is not suitable for all types of structures. Slip formwork techniques are adopted with more than 16 m height structures.
Slip formwork totally depends upon automation erection techniques. It considers about 7.2 m per day which is the fastest erection procedure in the construction industry. As it is a very rapid and time-saving erection technique and less labor is required hence economical.
Components Of Slip Formwork
Vertical forms are made of metal, wood staves, plywood, glass-fiber reinforced plastic, or a combination of these materials. The main function of vertical form is to shape the concrete.
Wales are used to hold vertical forms in place. It also supports scaffolding and other platforms.
Yoke legs are provided to lift and hold the weight of the entire structure. It safely transmits the lifting forces from the jacks to the wales. Yoke legs are also used to connect with the beams, scaffolding, and other supporting platforms.
Jacks are mounted on jack rods providing the necessary lifting force to the entire slip form system.
They are climbed up by jacks.
Types Of Slip Formwork
The different types of slip formwork are discussed below.
1. Vertical Slip Formwork
The vertical slip forming technique uses the extrusion concept in concrete construction. It depends on the quick setting properties of the concrete that is required between the initial strength gain with the ability to work.
So during the concreting process, the concrete form and working platform are raised together in a continuous vertical sliding motion utilizing hydraulic jacks.
2. Horizontal Slip Formwork
Horizontal slip form is used for pavement and traffic separation walls. In this method, concrete is laid down, vibrated, worked, and settled in place while the form itself slowly moves ahead.
3. Cantilever Jump Form Method
This slipforming method is used for climbers which are independent of cranes. It is attached to a large formwork area at story height. This system gives maximum protection, providing a complete self-climbing formwork system that is independent of cranes for walls, columns, supports, and floor beers.
4. Egg Shaped Slip Form System
This system is based on the jump form principle which can be adapted to any geometric shape. Individual curvature adjustment can be done by adjusting the axis and vertical circumferential slope. It can be adjusted independently on each side of the wall and products of optimal working condition.
5. Canonical Slipformwork
Canonical slipforming offers monolithic construction of decreasing and increasing layouts without any steps. For slipforming variable cross-sections, horizontally moveable formwork structures are used. These are mounted on hydraulically adjustable tapering elements.
The overhead girder star with its centerpiece forms the central point of the tower and connects all main beams to a uniform, closed scaffolding. At the same time, it serves as an upper work platform.
The conical slipforming technique has been developed to construct structures with continuously changing dimensions and wall thicknesses.
Advantages Of Slip Formwork
- Non-stop rapid concreting. At least 4 times faster.
- High production rates.
- Provision of a joint less structure.
- Scaffoldings are not required.
- Better finishing of concrete.
- Reduced labour cost.
- Workers get a safe working environment for the job.
- Provides more working space.
- Slip form technique eliminates the use of cranes.
- Plastering is not required.
- Saves formwork materials.
- Strength and accuracy are more than regular work.
- Uniform wall sections and layouts are obtained.
Disadvantages of Slipform Construction
- Very high initial cost.
- Time consuming process for arranging various components
- Requires expert supervision and operations.
- Materials can not be stocked easily on the site.
- Good coordination and site organization are required.
- Large quantities of equipment (e.g. generators, lighting systems, and hoists) are required.
- The work must be continued in any weather
1. Working platforms, guard rails, ladders, and windshields should be built into the system.
2. The completed formwork system is sturdy.
3. Concrete strength should be checked at a certain period of intervals.
4. Workers can quickly become familiar with the health and safety aspects.
5. All parts should move at a uniform rate, no jam in formwork or jack should be present.
6. Forms must have lateral supports.
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