More than half of the global population now live in cities, and by the end of the century another 3 billion will have followed, so high rise construction is an essential way to achieve sufficient population density in urban development and to avoid urban sprawl into the countryside.
Whereas the earliest skyscrapers were purely office towers, many of today’s high profile towers combine residential, commercial, leisure and even green space into a kind of vertical village. Another trend is for slender high rise luxury residential projects. These have an astonishing height-to-width ratio far beyond 9:1.
Climbing tower cranes working on inner city residential super tall projects often have to cope with limited set up space as a result of surrounding infrastructure, neighbouring buildings and the narrow core and lift shaft size of the building under construction.
In addition, the wide application of concrete requires fast load cycles. Strong competition among tower crane manufacturers drives provision of special slim tower systems under 2 x 2m for internal climbing.
For example, in 2009, Favelle Favco delivered a compact 223.19 type 1.9 x 1.9m tower for the London Pinnacle project in the UK. For an Australian apartment tower project, a step down to the even slimmer 1.6 x 1.6m type 223.16 tower system was made.
A transition tower section provides adaptation to the standard 2.017m slewing ring support of the upper crane. On the Favelle Favco M220DX luffing jib tower crane with 30m boom, a free standing height of 40.6m can still be achieved with the 223.16 tower system.
Access in narrow lift shafts is afforded by a vertical connection device, consisting of six bolts per angle in the pockets of the reinforced main chords of the mast. Nothing extra is needed for removing horizontal connection devices when de-rigging the internal climbing tower crane after topping out the core.
Adding to the compactness is the three beam internal climbing system. Space constraints can become a major issue when conventional climbing collars or systems using leaders, plus the formwork, force the use of a smaller crane than is possible using the three-beam lift shaft climbing device. During the first climbing step of a three-beam system, the middle beam extends at both ends into core wall pockets while telescopic sections of the two other beams are retracted.
After jacking the crane by the amount corresponding to the length of the central hydraulic stroke, the two lateral beams are extracted from the core wall pockets leaving the whole crane supported on the next working level. Then the hydraulic cylinder with the central retracted beam follows up into the working position of the crane.
Three-beam climbing systems were originally widely used on Favelle Favco cranes. They are self-contained and minimise the preparation work needed before jumping a crane. They require, however, protrusions in the core at many short intervals as defined by the cylinder stroke of the climbing unit.
On Jaso J208PA and J280PA luffing jib cranes, the Spanish manufacturer developed a similar climbing device based on 1.7 x 1.7m towers to fit 2.09 x 2.09m lift shafts for its Australian representative.
Adjacent high rise buildings and other neighbouring obstacles demand a short out-of-service position in the initial phase of the construction project. To accommodate this, Jaso developed a folding structure acting as an additional boom stop which can be manually or automatically activated when the crane is parked in a steep out-of-service position.
The J280PA can be parked with a 30m jib at only 5.75m radius. To help the crane to weathervane, a large windsail banner was added at the jib end.
For the Crocus City Manhattan project in Moscow, Russia, two J280PAs were delivered climbing inside the building’s core. Both had the special Jaso jib park system so that the 40m booms could weathervane at 7.5m radius instead of the standard 16m.
On such cramped sites, Favelle Favco fits a storm parking system consisting of separate hydraulic buffers added to the A-frame, against which the boom is parked in a raised position.
Instead of using a common fixed windsail banner, Select is delivering its new Terex luffing jib cranes in London, UK, with a curtain-like windsail.
When the crane is working, the windsail will be folded and parked in a shelter on the tip jib section. For weathervaning, the crane driver activates an electric motor, pressing a button in the cabin to unfold the banner which is guided in a curtain track inside the jib.
In contrast to three-beam climbing, a typical climbing system from European manufacturers allows more flexibility as the crane can jump several levels in a single climb without needing core wall pockets arranged close together.
In this case, the inner climbing crane is resting on a set of two climbing collars surrounding the crane tower which, in turn, are based on custom-designed sub-beams connected to the core wall.
By using the hydraulic ram in the base tower section climbing catch hook past, and then rest on, ladder rungs moving up the crane. The whole crane is held by a ladder fixed to the lower climbing collar during this process.
After the crane has climbed through the first collar, crane supports extended at the base tower section will rest on this collar while the ladder has to be moved to the second collar above. Before jumping the crane to the next level, a third upper collar must be installed, including sub-beams. It will guide the crane when leaving the lowest collar.
Even using a slim tower system, the dimension of the climbing collars must also fit into the lift shaft. To save space and climbing time for the core construction, crane manufacturer Wolff developed a special version of its new KSH 23 inner climbing device.
Fitted with collars, the necessary floor opening is 3.54 x 3.19m for the 2.30 x 2.30m tower system. Without the collars, the modified ladder climbing system, called KSH E 23, can be installed in a 2.70 x 2.70m opening.
Without collars a new guide system for the tower and a connection point for the ladders must be found. Two telescopic cross beams with extendable shoes replace the upper collar and sets of mast corner guides. To clamp the tower they must be fixed to the core wall.
During operation the whole crane is resting on a massive extendable support girder which is integrated in the lowest climbing tower element. When climbing, the support girder is retracted and catch hooks at the piston cross beam fall out and latch into the climbing ladders.
Regardless of whether a Wolff KSH 23 standard or a modified KSH E 23 internal climbing version is used, the 2.30 x 2.30m tower system with strong corner posts is very resistant to torsional distortion. Its characteristics allow the tower to be up to 36m above the clamping of the internal climber. It is suitable for internal or external climbing so it brings flexibility to the construction site.
Terex has an improved HD19 26.6.ladder climbing system. It was used for the first time installed on the two CTL430-24 core climbing cranes raising the 40 storey 100 Bishopsgate project in east London, UK. No climbing collars or sub-beams are used with this internal climbing device. Core wall pockets in the elevator shaft allow positioning of the climbing ladder support beams during climbing and crane supports during crane work.
During a climbing operation, specially shaped catch hooks flip by gravity into the lugs when passing the ladder. Two guiding fix frames connected to the base section and third tower section allow continuous climbing. By using transfer mast sections, CTL 180-CTL430 luffing jib tower cranes can be mounted on the slim 1.90 x1.90m mast system.
The speed at which the core can be raised by slipforming is key to making good progress, to provide stability as the building takes shape. The tower cranes need to grow at the same speed to ensure that a light weight crane can be installed on top of the slipform with a fixed short tower length.
Alternatively, the crane following the rising core must be fast climbing to minimise its time out of service for climbing. A solution is to choose a rigid compact tower system allowing high free standing capacity above the last tie-in support to the building.
For larger cranes up to the 1,000 tonne-metre class, Liebherr developed its new 24HC monoblock tower system with an outer dimension of 2.40 x 2.40m. It is suitable for internal and external climbing. An impressive 74.80m free standing capacity can be achieved for the new 710HC-L luffing jib crane rigged with 30m jib.
Component weight is important, as it dictates the size of the derrick crane needed for dismantling. In addition to the crane upper, on an internal climbing crane it is also important to consider the weight of the internal climbing system components. To that end the new 24HC internal climbing section can be easily split in two tower sections by the standard tower connection devices.
As the core rises, the installation of permanent lift shafts is a substantial benefit to accelerate construction time. As each floor is constructed around the core, the lift capacity is already there to serve it. In comparison to external construction hoists, hours can be saved for each worker just travelling up and down by using the building’s super-fast lifts inside the core. In this case, however, the crane should be installed externally.
A solution can be conventional tie-in support frames. For buildings with only one rigid core surrounded by open space floors that means long, custom-designed tie-in supports, which soon become expensive and an obstacle to the complex facade installation.
In addition, the crane will lose its central position in the building under construction, leading to significant expense for extra mast sections and higher capacity because of the requested extended outreach.
A solution is to climb the crane outside the core. In normal operation, two out of three supporting brackets are used to secure the crane at the outer core wall. For jacking operations, three brackets alternate.
While the upper frame tightly holds the crane tower with horizontal loading acting on it, the lower frame has to take the vertical loading as well. Forces generated can be absorbed either by compression members under the frame or tension members above it, or a combination of both is preferred in order to distribute the loads.
A longer version of this feature appeared in the September 2016 issue of Construction Europe’s sister publication International Cranes and Specialized Transport.