High rise construction - the rise of the super skyscraper
By Helen Wright10 September 2013
This year has seen the topping out of two 500 m+ tall high rise buildings – the first was the 541.3 m One World Trade Centre tower in New York, US, which became the tallest building in the country when the final section of a 124.4 m steel spire was lifted in to position in May.
Then the 632 m Shanghai Tower in the Chinese city’s Lujiazui commercial district became the second tallest building in the world behind the 828 m Burj Khalifa in Dubai, UAE, when it topped out in August.
But as any watcher of skyscraper developments knows, these titles are never held for long. More super high-rise buildings are planned around the world, including the 1 km tall Kingdom Tower in Jeddah, Saudi Arabia. China is planning further 500 m+ developments, including the 838 m tall Sky City tower in Changsha, Hunan province, as well as the 636 m Wuhan Greenland Center in Whuan.
Such immense structures present challenges for architects, contractors and construction equipment manufacturers alike. Take something as innocuous as the internal lifts, for example. Until recently, designers had to live with the fact that a building’s elevators were limited to a maximum height of around 500 m due to the weight of the steel cable.
Manufacturer Kone has been working on this issue, and this year launched an alternative to steel rope, Ultra Rope, which has a carbon fibre core and a high-friction coating. Kone claims this can double elevator travel heights to up to 1,000 m by reducing rope weight and the overall elevator moving mass.
Indeed, Kone says Ultra Rope’s lightweight carbon fibre core cuts elevator moving masses by up to -60% compared to steel – a fact that it says has opened up a world of possibilities in high-rise building. The lifetime of carbon fibre is also said to be at least twice that of conventional steel rope, and no lubrication is required to maintain it thanks to its coating.
As well as playing a significant part in the internal workings of a completed high-rise structure, hoists and winches have a key role during the construction process. Alexandre Chanteclair, tower crane product manager for Europe, Africa and the Middle East at Potain, said it was important to plan the length and strength of hoists and winches on high-rise projects.
“The tallest high-rise tower cranes need vast lengths of rope to carry loads to such great heights, and often work with two or more falls,” Mr Chanteclair said. “A special study is carried out before erecting a crane beyond its maximum free standing height. Calculating the weight of hoist rope needed is an important part of this planning. Certain projects require drums with more than 1,000 m of winding capacity and we offer models with more than 1,100 m capacity.
“Another key aspect of working at height is the winch and its working speed. A weak winch can make for slow progress at a jobsite. And the strain placed on the winch can cause problems and delays,” he explained.
Potain has introduced a new range of high performance winches, one of which (the 75 HPL 30) can reach speeds of up to 225 m/min, making it the first to break the 200 m/min barrier, according to the company. The latest new winch to be introduced is the 270 LVF, a 200 kW-rated unit which can handle loads of up to 40 tonnes in four falls at a maximum speed of 162 m/min.
Keeping to tight schedules and avoiding potentially costly project overruns are key challenges on high-rise developments. Manufacturers are demonstrating that they are prepared to work closely with contractors to make sure the right tools for the job are on site at the right phase in construction.
The fabrication of concrete elements plays a central role in the construction of most skyscrapers, and formwork companies are constantly working to improve the efficiency with which the core and floor slabs of a building can be put in place.
Peri, for instance, is working with contractor CJSC Renaissance Construction to ensure that the Evolution Tower, a new high-rise landmark in Moscow, Russia, gains 4.3 m in height each week during the peak of construction.
The tower will be 249 m when complete in 2014, and form an iconic part of Moscow City – a new business district. Each floor of the tower twists 3o in relation to the preceding one, arranged around the central core of the building, making the entire structure twist clockwise from its base by more than 150o.
Peri engineers developed a crane-independent formwork system on the basis of its RCS and ACS self-climbing ranges. The ACS system was used with Peri’s Vario GT 24 wall formwork for the building core, while customised Uniportal slab tables were used to form the floor slabs and a diagonally climbed RCS climbing protection panel and landing platform accompanied every phase.
Core walls and floor slabs were concreted in one pour, with each floor divided into three concreting sections. Peri said the special feature of its solution for the Evolution Tower was the combined climbing formwork for the vertical core walls and twisted corner supports, together with the diagonal protection panels and landing platforms.
This bespoke approach has allowed the slab and column formwork to progress quickly and smoothly up the tower, and is helping the project stay on-track for completion, according to the company.
Doka is also working on high rise projects around the world, and is supporting contractor Tidhar Construction on the Shahar Tower in Tel Aviv – a 200 m building that will become one of the tallest in Israel once complete in 2016.
Most of the foundation castings for the project had to be completed during the night as the construction site is located at the centre of Givattayim City, a major intersection at the heart of metropolitan Tel Aviv. Doka said around 3,500 m3 of concrete were supplied to the site in the space of twelve hours.
Once the foundations are complete, climbing formwork from Doka including SKE50 automatic, Top 590 large-area, MF240 and Frami Xlife will be used to cast sections of the tower. The manufacturer’s Xclimb 60 self-climbing protection screen will also be used to help ensure a safe working environment on higher levels of the building.
Indeed, safety is another crucial aspect for contractors to consider on high-rise developments, not only for workers at the top of the building, but for anyone on the ground below. Many high-rise developments are, by their very nature, being constructed in urban areas, and this is certainly true of Saudi Arabia’s US$ 8 billion King Abdullah Financial District, where 40 multi-storey towers are currently under construction across a 1.6 km2 site.
Scheduled for completion in 2016, the development will host banks, financial institutions and professional service companies. But construction is presenting a logistical challenge, with almost complete multi-storey buildings under construction next to foundations where piling work has yet to begin, according to manufacturer Combisafe.
A total of 1,450 steel mesh barriers and multi mesh barriers have been supplied by Combisafe across the King Abdullah Financial District. With so many people at work across clusters of buildings, Combisafe said edge protection and fall safety systems were vital to ensure optimum safety at all times.
Offering a projection of 3.3 m, these safety nets are designed to absorb falls from heights of up to 6 m. In addition, Combisafe supplied 18 Preston Superdeck platforms, which provide access for heavy building materials to be delivered by crane to high-rise buildings. The platforms extend 4.5 m out from the side of a building and can carry up to 5 tonnes.
As work on any high-rise development progresses, contractors will face new sets of challenges. These include how to remove the equipment that has been climbing with the building as construction nears completion.
Contractor Larsen & Toubro (L&T) used a Liebherr 200 DR 5/10 Litronic Derrick crane to dismantle a tower crane that had been used to help construct the country’s tallest commercial building – the 220 m Kohinoor Tower in Mumbai, India, which topped out this year.
According to Liebherr, towers above 200 m tall are becoming more and more common in India. The 200 DR 5/10 can dismantle cranes weighing over 300 tonnes, and can lower heavy parts from great heights while preserving a safe gap between the part and the building.
Once the Kohinoor’s tower crane had been dismantled and lowered to the ground, the derrick crane was stripped down in to its individual parts and lowered into the buildings lift shafts.
The maximum dimensions of the individual components are 2.2 by 1.1 m by 1.1 m, and the maximum weight of any one component is 1,000 kg.
David Griffin, sales director at Liebherr-Werk Biberach, said, “We see huge potential for the execution of several dismantling projects using the Liebherr derrick crane on L&T sites. In fact, there would appear to be enough work for additional derrick units in India.”
Nearly 600 buildings of 200 m or more are currently under construction or planned to be built around the world over the next few years, according to the Council on Tall Buildings and Urban Habitat. And plans are already in place for 20 more 500+ m towers to be built in the future.
With new records being broken in the high-rise sector every few years, it will certainly be interesting to see how manufacturers continue to experiment with very strong, but light-weight materials like carbon fibre in the coming years.