Climbing Formwork System

What is Climbing Formwork

Climbing formwork is a self-supporting vertical formwork that ascends alongside a cast-in-place concrete structure. Rather than being fully struck and rebuilt at each level, the wall formwork together with its working platforms, access ladders and protection enclosure is assembled into a single climbing unit. After a wall section has been poured and has gained sufficient strength, the unit is unbolted from the hardened concrete, lifted one lift height, realigned and locked off for the next pour. The same panel set is therefore reused for every identical storey, which is the central economic argument for the method on repetitive high-rise work.

A complete climbing unit is more than a mould. It comprises four functional layers: (1) the wall formwork itself, a panel and waler assembly carrying the fresh-concrete pressure through form ties or, for single-sided work, through inclined struts; (2) the main pouring platform at the top of the new lift, where concrete is placed, compacted with a concrete vibrator and reinforcement is fixed; (3) the intermediate and suspended platforms that hang below, giving access to recover form ties, patch tie holes and reset the climbing cones; and (4) the embedded anchoring, the climbing cones and shoes cast into the wall that carry every load back into the structure. Because the unit is a temporary structure occupied by people at height, it is treated as falsework and is governed by temporary-works design rules.

Climbing formwork is best understood by what sits on either side of it. Conventional wall formwork is the simplest and is dismantled and re-erected at each level, with the platforms either separate or absent; it is economical for low-rise and irregular work but slow and crane-hungry on tall repetitive cores. At the other extreme, slipform rises continuously, typically 150 to 300 mm per hour, in an unbroken monolithic pour that may run around the clock and is suited to tall uniform shafts such as silos, chimneys and bridge pylons. Climbing formwork is the cyclic middle path: it produces a clean horizontal construction joint at each lift, tolerates interruptions and changing wall thickness, and is the dominant choice for high-rise building cores.

The technique grew out of the demand for taller reinforced-concrete cores and towers through the second half of the twentieth century. Early systems were entirely crane-dependent: the formwork was struck and re-hung by the tower crane at each level. Hydraulic self-climbing systems, which carry their own jacks and climb on embedded rails without occupying the crane, were developed to break the dependence on crane hours on congested, very tall projects. Today the major formwork houses offer a graded range from simple crane-climbed brackets up to fully automatic hydraulic climbers, and the engineering centre of gravity has shifted from the formwork face to the anchoring, the platform load classes and the wind design.

Four engineering questions decide whether a climbing system is fit for a project: how the unit climbs (crane, guided or self-climbing), what loads the platforms and anchors must carry, what lateral pressure the fresh concrete imposes on the form face, and how the system behaves in wind. The remaining chapters address each in turn, because a climbing system that is mis-specified on any one of these is not merely inefficient but a safety hazard suspended over the public realm for the full height of the building.

Climbing Formwork Types

Climbing systems are classified by how the unit is raised and whether it remains connected to the structure during the climb. Three families dominate: crane-climbed jumpform, guided-climbing jumpform, and self-climbing (automatic) systems. A fourth category, single-sided climbing formwork, is distinguished by its load path rather than its climb mechanism, and slipform is included for contrast even though it is a continuous rather than a climbing method. The table below compares the families on the dimensions that drive selection.

Crane-climbed jumpform is the simplest family. The formwork and its climbing bracket are repositioned by the tower crane: the unit is unbolted from the hardened wall, lifted clear and re-landed on cones cast into the new lift. It carries the lowest rental and engineering cost and is well suited to walls and cores up to roughly five to fifteen storeys, or to projects where the crane has spare capacity. Its limitation is that each climb consumes crane hours and exposes the unit to a free crane lift, so it cannot proceed in high wind and competes with material handling for the crane.

Guided-climbing jumpform adds a guide that keeps the unit anchored to the structure throughout the lift. The crane still provides the lifting force, but the unit slides up a guided track rather than swinging free, which improves control and safety and allows climbing in stronger winds than an unguided lift. Doka Xclimb 60 and PERI guided-climbing systems sit in this family. It is the common compromise for mid-rise cores where full self-climbing is not justified but a free crane lift is undesirable.

Self-climbing, or automatic, systems carry their own hydraulic jacks and climb on rails embedded in the wall below, with no crane involvement. PERI ACS and Doka SKE50 / SKE100 are representative: a hydraulic ring main can drive many climbers simultaneously, the unit is restrained on its rail at all times, and a single long-stroke cylinder raises one level in around 20 minutes on PERI ACS Core 400. Because the climb is crane-free and guided, it can proceed in higher winds and removes the crane from the critical path, which is decisive on towers above about twenty storeys and on congested sites. The cost is higher rental, more embedded hardware and more engineering.

Single-sided climbing formwork is used where there is no opposing face to tie against, such as dams, sluices, lock walls and retaining structures. The lateral concrete pressure is resisted by braces and struts bearing on the wall already cast below rather than by ties spanning to a second form face. It can be crane-climbed or self-climbing in its raising mechanism, but its defining feature is this one-sided load path, which makes the anchorage into the previous lift especially critical.

Climb Mechanisms and Anchoring

Whatever the family, every climbing system transfers all of its loads, the platforms, the formwork and the fresh-concrete pressure, back into the previously cast wall through embedded anchors. Understanding the climb mechanism and the anchoring chain is more important than the panel face, because this is where the system is structurally and safety critical. The table below compares the three mainstream climb mechanisms on their key engineering metrics.

The crane-climbed mechanism relies on the tower crane for lifting force. After the cones are reset on the new lift, the crane hooks the unit, lifts it one storey and lands it on the new shoes; the crew then bolts off, plumbs the form and pours. It is mechanically the simplest, but the climb is a free crane lift, so it is bounded by the crane wind limit and competes with all other crane tasks on site. Reliability of ready-mix concrete supply and crane scheduling, rather than the climb hardware, sets the achievable cycle.

The hydraulic self-climbing mechanism replaces the crane with jacks acting between the climbing unit and a guide rail or climbing profile anchored to the wall. The jack pushes the unit up the rail in a series of strokes, or in one long stroke on modern long-cylinder systems, while pawls engage successive rail teeth so the load is never released. On Doka SKE systems a hydraulic ring main can drive a large group of automatic climbers in unison so an entire core platform rises together, while PERI ACS resists 200 km/h out of service and remains operable up to 100 km/h, with a lower limit governing whether a climb may proceed. The unit is guided and restrained at every instant, which is why crane-free climbing is permitted in higher winds than a free crane lift.

The anchoring chain is common to all families and is the governing structural check. During each pour a climbing cone or anchor is cast into the fresh wall at the designed positions. On the next lift a recoverable suspension bolt or climbing shoe is fitted into that cone and carries the unit. Self-climbing systems add a guide rail bolted to a vertical column of climbing shoes anchored across several lifts below, so the rail is restrained at multiple levels during the climb and the load is shared. Anchor tension capacities commonly run in the order of 70 to 150 kN per anchor depending on the system, and the concrete must reach a minimum strength, typically 10 to 15 MPa, before any anchor is loaded. The temporary-works designer must verify anchor type, layout, edge distance and the concrete strength achieved at the time of loading.

Two failure modes dominate the anchoring design. The first is loading a cone before the concrete around it has gained the required strength, which can pull the cone out or spall the surrounding concrete; this is why stripping and climbing strength is a hold point confirmed by cube or maturity testing. The second is mis-positioned or omitted cones, which concentrates load on the remaining anchors. Both are procedural risks controlled by the Permit to Load and Permit to Strike regime under BS 5975 and equivalent temporary-works systems, not by the formwork hardware alone.

Loads, Pressure and Standards

The design of a climbing system is dominated by three load cases: the service load on the working platforms, the lateral pressure of the fresh concrete on the form face, and the wind load on the whole exposed unit. Each is governed by a specific standard and each must be satisfied at every stage of the climbing cycle, including the out-of-service condition. The platform service loads are classified to EN 12811-1, the same working-scaffold standard that governs site scaffolding, summarised below.

Platform loads. The main pouring platform at the top of the unit usually targets Class 3 or Class 4 because reinforcement, embeds and tools accumulate there during a pour, while the suspended striking and trailing platforms below are commonly Class 2 since they are used mainly for tie recovery and patching. Designing every deck to the highest class is wasteful and adds dead weight that the anchors must carry, so platform classes are assigned deck by deck to the work actually done on each level.

Fresh-concrete pressure. The lateral pressure of fresh concrete on the form face is the load case that sizes the panels, walers, ties and brackets. In European practice it is calculated to DIN 18218, which EN 12812 references for falsework; ACI 347 gives an equivalent formulation in the US. The maximum horizontal pressure rises with the pour rate, the fluidity of the mix (consistency classes F1 to F6, or self-compacting concrete), the fresh unit weight of roughly 25 kN per cubic metre, and the time to initial set, which is strongly temperature dependent. Pressure increases with the cast height equal to pour rate multiplied by setting time, up to a hydrostatic ceiling. Fast pours, very fluid mixes and cold, slow-setting concrete all raise the design pressure, and self-compacting concrete is normally designed for close to full hydrostatic pressure, which is why pour rate is a controlled parameter on site rather than left to the gang.

Wind load. Because a climbing unit is a large area suspended high on the building, wind governs both the in-service and out-of-service conditions and is assessed to EN 1991-1-4. Manufacturer systems quote both an operating wind limit, the speed below which a climb may proceed, and a survival wind speed for the parked unit. PERI ACS, for example, is designed to resist wind speeds of 200 km/h out of service and is operable up to 100 km/h, with a lower climbing-condition limit governing the actual lift decision. Protection screens and enclosures raise productivity and worker comfort but increase the wind area, so they must be included in the wind calculation rather than treated as cladding.

These load cases are pulled together by a temporary-works framework. In the UK, BS 5975 requires the appointment of a Temporary Works Coordinator, a Temporary Works Register, independent design checks to a defined category, and live Permit to Load and Permit to Strike controls. EN 12812 sets the falsework performance and design basis across Europe, and in the US ACI 347 guides formwork design while OSHA 29 CFR 1926 Subpart Q governs concrete and formwork safety. The manufacturer general-assembly drawing and load tables are a starting point, never a substitute for a project-specific design that verifies the actual anchors, concrete strengths, pour rates and wind exposure on the job.

Key Specification Parameters

Comparing climbing systems on a like-for-like basis means reading the manufacturer load tables and general assemblies for the parameters that actually constrain the job. Across the major systems, eight parameters drive the decision: platform load class, anchor (cone) tension capacity, climbing unit height and lift height, hydraulic cylinder capacity, climb speed, operating and survival wind speeds, minimum concrete strength at climb, and the number of climbers a single hydraulic unit can drive. Each is explained below.

Platform load class and deck width set how much material and how many workers a platform can carry, to EN 12811-1 as in Chapter 4. Deck width and the depth of the suspended platform below also determine whether form ties can be recovered and tie holes patched from the unit without separate access, which is a real productivity differentiator between systems.

Anchor (cone) tension capacity is the single most important structural number, because the whole unit hangs from these anchors. Capacities commonly run in the order of 70 to 150 kN per anchor depending on the system, and they are only valid above a stated minimum concrete strength. A higher anchor rating allows fewer anchors or heavier platforms, but it must be matched to the wall reinforcement and edge distances on the actual structure.

Lift height and unit height define how much wall is cast per cycle and how many platforms the unit spans. A taller lift means fewer climbs over the height of the building but a larger pour, higher concrete pressure and a heavier unit; lift heights are commonly in the order of 3 to 4.5 m to suit normal storey heights, with taller pours used on uniform shafts.

Hydraulic cylinder capacity and climb speed apply to self-climbing systems. Cylinder lifting capacities run into the tens of tonnes; the PERI ACS Core 400 long-stroke cylinders are rated at 40 tonnes and raise one level in about 20 minutes, while Doka offers SKE50 and SKE100 automatic climbers with 5 and 10 tonne lifting capacities respectively. A hydraulic ring main lets one power unit drive many climbers in unison: Doka quotes as many as 20 automatic climbers from a single hydraulic unit, which is what allows a whole core platform to climb together.

Operating and survival wind speeds bound when the unit may climb and what it must survive parked, assessed to EN 1991-1-4. The operating limit is the practical productivity constraint, since high-wind days stop the climb; the survival speed must envelope the local design wind for the exposed height and the platform enclosure area.

Minimum concrete strength at climb is the hold point that ties the formwork cycle to concrete technology. Anchors and brackets may not be loaded until the wall reaches the stated strength, typically 10 to 15 MPa, confirmed by cube or maturity testing. This parameter, more than the climb hardware, sets the achievable cycle, because warmer concrete and accelerating admixtures reach climb strength sooner and shorten the cycle.

The output of reading these parameters is a like-for-like comparison rather than a single accuracy figure. Two systems quoting the same platform class can differ sharply on anchor rating, climb-in-wind limit and how many climbers one power unit drives, and those differences decide programme reliability on a tall, wind-exposed core far more than the headline rental rate.

Selection Decision Factors

To turn the preceding chapters into a chosen system, follow the decision sequence below. Most selection mistakes come not from one wrong parameter but from deciding the climb family before the structure, the crane strategy and the wind exposure are understood. These eight steps work as a fixed RFQ template for a climbing-formwork enquiry.

1. Structure and height: Define the geometry first, core, shear wall, single-sided wall, pylon, and the number of repetitive lifts. Repetition and height are what make a climbing system pay; below about five storeys conventional wall formwork is usually cheaper, and very tall uniform shafts may favour slipform.
2. Climb family: Choose crane-climbed, guided-climbing or self-climbing based on crane availability and height. Crane-climbed suits low to mid-rise with spare crane capacity; self-climbing becomes decisive above about twenty storeys, on crane-constrained sites and in high wind, because it removes the crane from the critical path and stays guided at all times.
3. Anchoring and concrete strength: Confirm the anchor (cone) tension capacity, layout and edge distances against the actual wall reinforcement, and fix the minimum concrete strength at which anchors may be loaded (typically 10 to 15 MPa). This is the governing safety check, not an afterthought.
4. Platform load classes: Assign EN 12811-1 classes deck by deck, Class 3 or 4 for the main pouring platform, Class 2 for suspended striking and trailing decks, so the unit is neither under-strength nor needlessly heavy.
5. Fresh-concrete pressure and pour rate: Calculate the form-face pressure to DIN 18218 (or ACI 347) for the planned mix, temperature and pour rate, and set a controlled maximum pour rate. Self-compacting concrete generally requires designing for near full hydrostatic pressure.
6. Wind design: Establish the operating and survival wind speeds to EN 1991-1-4 for the exposed height, including the area of any protection enclosure, and confirm the system climb-in-wind limit suits the site exposure and programme.
7. Cycle and programme: Target a realistic cycle, three to five days per storey, and recognise that it is set by concrete strength gain and leading-edge management, not by climb speed. Plan concrete supply, rebar prefabrication on a rebar bender and crane sharing to protect the cycle.
8. Temporary-works governance: Require a project-specific, independently checked temporary-works design under BS 5975 or the local equivalent, with a Temporary Works Coordinator, Permit to Load and Permit to Strike. The manufacturer general assembly does not replace site-specific verification of anchors, concrete strength and wind.

One last commonly overlooked dimension is supplier serviceability: local availability of spare parts, hydraulic-pump service and trained supervision, the quality and responsiveness of the engineering and design-support team, and the supplier ability to deliver a checked temporary-works design rather than only a quotation. PERI, Doka, MEVA, Alsina and ULMA maintain engineering and equipment support across many regions, while GETO, Lianggong and Zolo serve large repetitive projects at competitive rental in Asia; on a safety-critical structure carried by people for the full height of the building, this support capability often matters more than the headline price.