When it comes to constructing high-rise building concrete cores, a contractor or specialist concrete frame sub-contractor must often decide whether the structural formation is best achieved using either a Slipform or a Jumpform type solution. Each system has its advantages, which will generally depend on factors such as the core height, the inclusion of complex design features, or the presence of concrete mixes that could affect performance outcomes concerning target strength to control the cycle processes, amongst other factors.
Although the processes differ in their movement and operation, as Tony Austin, High-Rise Business Development Manager at Doka explains, “Slipform and Jumpform construction is designed to achieve the same goal: a perfectly formed core that delivers the structural integrity for a high-rise building”.
Although the processes differ in their movement and operation, as Tony Austin, High-Rise Business Development Manager at Doka explains, “Slipform and Jumpform construction is designed to achieve the same goal: a perfectly formed core that delivers the structural integrity for a high-rise building”.
Press Contact
Due to the range of Jumpform products on the market, depending on the project and local constraints or demands, the specification process can be complex. Some sites have the required crane access and capacity to utilise simpler crane-climbed solutions. These can either be attached to the wall using a rail to help with easier movement or simply hooked onto the building. However, most sites will not have such crane capacity or do not want to risk weather affecting the movement of the core's construction when crane wind limits are reached.
To overcome these more typical constraints on site within the Jumpform system types, Automatic Self-Climbing formwork is by no means a recent phenomenon. It’s a well-practised method in the construction of lift and stair cores in high-rise buildings and other concrete infrastructure, including bridges and power stations, using hydraulic solutions to raise the systems to the next casting step. Yet, with all these options, selecting the correct method to form the concrete cores is far from a one-size-fits-all solution. Hence, there are stark choices when selecting an application-appropriate system.
When a structural core requires a rapid, join-free concrete finish, it may be tailormade for Slipform construction. Often used in conjunction with steel-frame commercial high-rise buildings due to the speed of the steel structure following the concrete core, the ability to complete the central lift shafts and stairwells as rapidly as possible is important. Although careful planning is a prerequisite, the continual pour method associated with a self-lifting Slipform rig is quicker than the Jumpform alternative. The Slipform method’s streamlined operation is aided by its use of limiting the need for cranage, except for ‘feeding’ the steel and concrete operations. Slipform operations are typically labour-intensive for the short period that the system is in operation, compared to the typically more “planned” Jumpform operations. However, a highly skilled workforce is required to oversee operations on both systems.
The more complex a building’s geometry, the more suited it is for automatic Jumpform construction. This is often the case where details, such as sheer wall or shaft designs, change and fluctuate throughout a building, to accommodate decreasing stair levels, for example. Automatic Jumpform systems may also be appropriate at drop-off utility or lift shaft sections, as well as to meet architectural requirements for a stairwell’s concrete core.
Due to the continuous pour process being a key Slipform feature, particular attention should be paid to the concrete’s setting times before its application. A different mix ratio of CEM I and CEM III cement can influence a concrete’s setting behaviour. The approximate optimum temperature for Slipform cast-in-place concrete is 20°C. The use of higher-grade cement (CEM I: 42,5 or 52,5) is recommended at lower ambient temperatures. A higher content of CEM III and after-treatment is advised for higher ambient temperatures.
In respect of Slipform concrete composition, a maximum aggregate size of circa 22mm is advised, with rounded grain preferred to crushed grain. Typically, a 0.5 water-to-cement ratio is ideal for Slipform projects.
In terms of mix and set times, generally, a Jumpform core contains a minimum C40 mix, typically a group 3,4,5 concrete mix, C2, 0.45. For Jumpform projects, which take place over wider temperature ranges i.e; projects in summer and winter, it is recommended to have 2-3 alternative concrete mixes approved to react to temperature fluctuations and maintain consistent cycle times. However, always consider the impact of these changes of concrete mix on finish factors, particularly when the project demands fair-faced architectural finishes on visible concrete sections. It generally takes approximately two-to-three days to achieve sufficient strength to jump the platforms to the next pour position. Generally, structures with Jumpform cores would work on a five or seven-day cycle per floor to complete concrete frame cores, wall, column and slab construction. Modern digital concrete maturity measurement techniques, such as those available via Doka’s ‘Concremote’ concrete monitoring system, help speed these cycle times, support with architectural colour matching and manage large pour crack mitigation and temperature control.
However, with the rig lifting approximately 25mm every few minutes, additional vigilance is needed to ensure the process is completed with the utmost accuracy. This is particularly pertinent with plate embedment and at areas such as door openings, door levels and floor continuity connections. In such potentially hectic environments, it’s imperative that contractors employ the services of an experienced engineer to oversee operations. Full-time Slipform supervisors are provided within all Doka Slipform proposals.
Rail-guided Jumpform systems offer equal but different safety advantages as they enable and deliver more preparation time between each concrete cycle and thus can inspire a calmer, more systematic approach to the concreting process when on site.
For Doka, the project involved the bespoke assembly and delivery of the forming system featuring boxes and shutters to enable the time and cost-effective completion of two concrete cores. These were central to two high-rise residential blocks, comprising 129 self-contained apartments. For each building, Doka provided a tailored Slipform system that was assembled off-site and delivered ready for operation.
For the 30-metre, ten-storey building, the Slipform process included the entire core, one staircase and two lift shafts. The slip formwork comprised two, rather than three, platforms – a hanging deck and main deck. This highlighted Doka’s capability to produce solutions to suit individual needs, which in this case required minimising site materials, speeding assembly whilst providing an economical solution for the project.
The hanging deck enabled the finishing processes to be undertaken safely and effectively for the core’s 250mm walls – the same wall-width as the 14-floor building – with the Slipform process enabling a daily climb of between 3.1 and 3.4 metres over a nine-to-ten-hour day. The formwork facilitated a six-day per week concreting process, with the equipment’s dismantling taking five days.
Ben Williams, Managing Director at Spencer Civil Engineering, which oversaw the concrete cores’ construction, said: “I was very impressed with the Doka bespoke Slipform system; it performed exactly how Doka sold it to us, with a high-quality finish – in comparison to other Slipform systems – and excellent speed of construction.”
The project involves the full redevelopment of the current estate and includes the building of 781 new homes, more than half of which will be designated affordable properties. Doka was selected by, Keltbray – working on behalf of Bouygues – to design and supply the equipment required to form the concrete structures for the redevelopment’s first phase. This meant providing a hydraulic Jumpform system and formwork for the safe, time-efficient construction of two residential blocks (buildings 7 and 8).
Doka supplied its automatic guided climbing formwork SKE50 plus and its heavier-duty SKE100 plus system for the buildings’ cores. The latter unit allowed operatives safe, integrated hanging access to the working levels from floors below. The construction sites’ limited space saw Doka support the build process by supplying some of the equipment and platforms as pre-built units. This allowed the site teams to focus on their core workflow processes, minimise storage and reduce start-up time on site.
Each residential block comprises 16 floors, hence, the formwork equipment required the capability to reposition several climbing units simultaneously in order to meet the client’s strict completion timeframe. The buildings’ core walls were created using Framax Xlife, Doka’s rapid-forming systemised formwork solution, used in conjunction with the SKE plus hydraulic climbing units.
To overcome these more typical constraints on site within the Jumpform system types, Automatic Self-Climbing formwork is by no means a recent phenomenon. It’s a well-practised method in the construction of lift and stair cores in high-rise buildings and other concrete infrastructure, including bridges and power stations, using hydraulic solutions to raise the systems to the next casting step. Yet, with all these options, selecting the correct method to form the concrete cores is far from a one-size-fits-all solution. Hence, there are stark choices when selecting an application-appropriate system.
When a structural core requires a rapid, join-free concrete finish, it may be tailormade for Slipform construction. Often used in conjunction with steel-frame commercial high-rise buildings due to the speed of the steel structure following the concrete core, the ability to complete the central lift shafts and stairwells as rapidly as possible is important. Although careful planning is a prerequisite, the continual pour method associated with a self-lifting Slipform rig is quicker than the Jumpform alternative. The Slipform method’s streamlined operation is aided by its use of limiting the need for cranage, except for ‘feeding’ the steel and concrete operations. Slipform operations are typically labour-intensive for the short period that the system is in operation, compared to the typically more “planned” Jumpform operations. However, a highly skilled workforce is required to oversee operations on both systems.
The more complex a building’s geometry, the more suited it is for automatic Jumpform construction. This is often the case where details, such as sheer wall or shaft designs, change and fluctuate throughout a building, to accommodate decreasing stair levels, for example. Automatic Jumpform systems may also be appropriate at drop-off utility or lift shaft sections, as well as to meet architectural requirements for a stairwell’s concrete core.
Concrete behaviours
Typically, all concrete approved for reinforced structures can be used for slipforming, the material’s basic parameters being defined by a structure’s architect or engineer. A sufficient number of fines in the concrete will enhance its capability to provide a join-free finish. However, it is important to remember the importance of continual adjustment and fine-tuning required to adjust the concrete mixes to suit the ambient temperature conditions and ensure the Slipform rig is working at its best productivity.Due to the continuous pour process being a key Slipform feature, particular attention should be paid to the concrete’s setting times before its application. A different mix ratio of CEM I and CEM III cement can influence a concrete’s setting behaviour. The approximate optimum temperature for Slipform cast-in-place concrete is 20°C. The use of higher-grade cement (CEM I: 42,5 or 52,5) is recommended at lower ambient temperatures. A higher content of CEM III and after-treatment is advised for higher ambient temperatures.
In respect of Slipform concrete composition, a maximum aggregate size of circa 22mm is advised, with rounded grain preferred to crushed grain. Typically, a 0.5 water-to-cement ratio is ideal for Slipform projects.
In terms of mix and set times, generally, a Jumpform core contains a minimum C40 mix, typically a group 3,4,5 concrete mix, C2, 0.45. For Jumpform projects, which take place over wider temperature ranges i.e; projects in summer and winter, it is recommended to have 2-3 alternative concrete mixes approved to react to temperature fluctuations and maintain consistent cycle times. However, always consider the impact of these changes of concrete mix on finish factors, particularly when the project demands fair-faced architectural finishes on visible concrete sections. It generally takes approximately two-to-three days to achieve sufficient strength to jump the platforms to the next pour position. Generally, structures with Jumpform cores would work on a five or seven-day cycle per floor to complete concrete frame cores, wall, column and slab construction. Modern digital concrete maturity measurement techniques, such as those available via Doka’s ‘Concremote’ concrete monitoring system, help speed these cycle times, support with architectural colour matching and manage large pour crack mitigation and temperature control.
Reliability of concrete supply
With Slipform construction, concrete needs to be delivered regularly and consistently without disruption between working windows, which could be anything from 9 to even 24-hour operations. Therefore, a batching plant must be located near its operational site. Delays in the pouring process could have detrimental time and productivity impacts. For this reason, Jumpform might be a more practical solution for construction sites in densely populated areas in towns and cities where vehicular access is limited or restricted and traffic congestion could have a negative impact on the reliability of concrete supply.Safety and vigilance
Generally, Slipform is viewed as a safe self-climbing formwork option due to the formwork process having few moving elements or parts which physically move away from the face of the core. Following an assembly and installation at basement level, there are no open joints to contend with on a rig’s upward journey.However, with the rig lifting approximately 25mm every few minutes, additional vigilance is needed to ensure the process is completed with the utmost accuracy. This is particularly pertinent with plate embedment and at areas such as door openings, door levels and floor continuity connections. In such potentially hectic environments, it’s imperative that contractors employ the services of an experienced engineer to oversee operations. Full-time Slipform supervisors are provided within all Doka Slipform proposals.
Rail-guided Jumpform systems offer equal but different safety advantages as they enable and deliver more preparation time between each concrete cycle and thus can inspire a calmer, more systematic approach to the concreting process when on site.
Case study: One Victoria, Manchester
Doka provided the Slipform systems to facilitate the rapid, high-quality creation of concrete cores at the One Victoria residential development in Manchester city centre.For Doka, the project involved the bespoke assembly and delivery of the forming system featuring boxes and shutters to enable the time and cost-effective completion of two concrete cores. These were central to two high-rise residential blocks, comprising 129 self-contained apartments. For each building, Doka provided a tailored Slipform system that was assembled off-site and delivered ready for operation.
For the 30-metre, ten-storey building, the Slipform process included the entire core, one staircase and two lift shafts. The slip formwork comprised two, rather than three, platforms – a hanging deck and main deck. This highlighted Doka’s capability to produce solutions to suit individual needs, which in this case required minimising site materials, speeding assembly whilst providing an economical solution for the project.
The hanging deck enabled the finishing processes to be undertaken safely and effectively for the core’s 250mm walls – the same wall-width as the 14-floor building – with the Slipform process enabling a daily climb of between 3.1 and 3.4 metres over a nine-to-ten-hour day. The formwork facilitated a six-day per week concreting process, with the equipment’s dismantling taking five days.
Ben Williams, Managing Director at Spencer Civil Engineering, which oversaw the concrete cores’ construction, said: “I was very impressed with the Doka bespoke Slipform system; it performed exactly how Doka sold it to us, with a high-quality finish – in comparison to other Slipform systems – and excellent speed of construction.”
Case Study: Ebury Bridge, Belgravia, London
Doka’s high-performance hydraulic guided Jumpform systems and framed formwork solutions proved pivotal to the safe, rapid construction of two buildings that are core to the Ebury Bridge residential redevelopment in central London.The project involves the full redevelopment of the current estate and includes the building of 781 new homes, more than half of which will be designated affordable properties. Doka was selected by, Keltbray – working on behalf of Bouygues – to design and supply the equipment required to form the concrete structures for the redevelopment’s first phase. This meant providing a hydraulic Jumpform system and formwork for the safe, time-efficient construction of two residential blocks (buildings 7 and 8).
Doka supplied its automatic guided climbing formwork SKE50 plus and its heavier-duty SKE100 plus system for the buildings’ cores. The latter unit allowed operatives safe, integrated hanging access to the working levels from floors below. The construction sites’ limited space saw Doka support the build process by supplying some of the equipment and platforms as pre-built units. This allowed the site teams to focus on their core workflow processes, minimise storage and reduce start-up time on site.
Each residential block comprises 16 floors, hence, the formwork equipment required the capability to reposition several climbing units simultaneously in order to meet the client’s strict completion timeframe. The buildings’ core walls were created using Framax Xlife, Doka’s rapid-forming systemised formwork solution, used in conjunction with the SKE plus hydraulic climbing units.
