High-rise construction: View from the top
By Laurel Henning07 September 2011
A key challenge to many new high rise developments in urban areas is finding the space to work while avoiding disruption to city life. This need to work in a limited footprint is one of the factors forcing equipment to progress.
New York's iconic One World Trade Center, for example, will stand at 541 m on completion of structural work this month - making it the tallest building in the US.
When construction began in April 2006 with the 60 x 60 m excavation of a 24 m deep hole, a single slab from the original tower separated the construction site from an existing subway line and 300000 daily commuters. Tishman construction, the contractor for this project, used a Schwing S 58 SX truck mounted concrete pump to start work on the site in summer 2007. This is Schwing's longest reach and most advanced concrete pump - without its Super X curved outriggers, mass pours of slabs, core walls and columns would have been very difficult in this crowded space.
Pump placement was critical for bringing the ready-mixed concrete to downtown Manhattan. A two pump, two boom, two pipeline system was used, which meant that a deck could be poured at the same time as a core pour was taking place on a different level.
The history of the site has drawn many spectators as it has progressed to 105 floors. The estimated cost of the building is US$ 3.1 billion, with 46000 tonnes of steel and 200000 m³ of concrete used in construction.
Logistical challenges due to crowded construction sites must also be dealt with in Europe. The narrow streets of Paris, France, can prove extremely problematic when a transport platform is needed in the renovation of an old building. This was the problem presented by Chastagner, a French rental company specialising in lifting equipment, to Bavarian hoist manufacturer Geda.
As well as the issues surrounding space limitation, there is no high voltage electricity supply in many old Parisian buildings.
To overcome such issues, a Geda 300 Z/ZP transport platform was chosen. With dimensions of 1.3 m x 0.8 m, it is designed for narrow spaces. The platform can also transport three people and material with a total weight of 300 kg, and has a lifting speed of 12 m/min. 400 V and 230 V versions are both available, removing the need for unusual electricity supplies.
Other companies are also developing their products to be more compact, which coincides with the difficulties of inner city construction. Linden Comansa's new LCL luffing jib range was completed this year with the launch of a fourth model, the LCL 165 crane. It incorporates all the characteristics of the rest of the LCL series - modular, light and compact design - as well as mechanisms which guarantee soft movements and electronic coordination between the luffing and hoisting movements, known as level-luffing.
Maximum loads range from 8 tonnes and 24 tonnes for the LCL 165 and the LCL 310. All mechanisms featured in the new series will also include the Effi-Plus system, which increases the hoist speed with light loads, improving productivity.
Easier and more precise assembly was the aim of Liebherr when it redeveloped its 200 EC-B 10 Litronic Flat-Top crane. Its successor, the 202 EC-B 10 Litronic has a lifting capacity of 2.2 tonnes at a maximum radius of 65 m, with an maximum load of 10 tonnes. The Liebherr 256 HC tower system allows for a free-standing hook height of 63 m.
One new feature is the single piece counter-jib, which is
2 tonnes lighter and can be pre-assembled on the ground.
Design adaptations to the slewing platform have reduced assembly weights by 1.6 tonnes, taking a total weight of the complete compact head to 8.8 tonnes. This weight reduction means that assembly can be carried out with small mobile cranes.
In Mumbai, India, building height restrictions are being eased. This change in a fast growing city suggests that Mumbai will soon be experiencing the difficulties with confined spaces that are already common in New York and Paris.
Developer and contractor NL Pvt has selected a Liebherr 71 EC-B 5 FR tronic flat-top tower crane to build a 30 storey apartment complex in Mumbai.
The Avrat residential building will reach a height of 110 m, and Liebherr's 71 EC-B 5 FR tronic crane will climb with the structure as it grows.
Although the site is on the fringe of open countryside, it is bounded on three sides by residential buildings of eight and 12 storeys.
"The excavation for the foundations is about 10 m deep," says NL's chief on-site engineer Prakash Parab. "The crane stands at about 45 m in height, so to comply with safety requirements for the surrounding buildings, we constructed this base on the site, and mounted the crane on that." The base is 5.5 m of steel and stands on a 2 m concrete block.
Construction time for the building is scheduled at two-and-a-half-years.
At the National University of Singapore (NUS), meanwhile, a residential complex comprising three high-rise buildings is being constructed.
In order to maintain a tight schedule, contractor Tiong Seng has been working with the latest formwork and scaffolding systems from Peri.
Wall sections, of up to 16.5 m in height and rectangular columns which stretch over five floors, have been constructed using Maximo panel formwork, while slabs were made with Skydeck panel and slab formwork.
Maximo is a system that can be adapted to match different building dimensions. The system uses MX Tie Technology, which is said to save time and resources using a newly developed conical tie system that does not require any spacer tubes and can be installed by one man from one side of the panel.
Together with the RCS rail climbing system, the Maximo wall formwork created moving units that were connected to the structure at all times. With the use of mobile climbing hydraulics, no cranes were needed.
The increasingly complex design of high rise towers poses challenges. As the number of skyscrapers increases, so too does the desire to be unique.
Following its involvement in the construction of the Burj Khalifa Tower in Dubai, Doka formwork will be used in the construction of a new series of super towers. The Lotte Super Tower in Seoul, South Korea the CMA Tower in Riyadh, Saudi Arabia and the Lamar Tower in Jeddah, Saudi Arabia are all to join the list of the world's tallest buildings.
The Lotte Super Tower in Seoul will reach 555 m. The core breaks down into three sections which are roughly equal in height but geometrically completely different. From August 2011, 117 SKE100 automatic climbers have provided support for the cast in-situ concrete core. They will also raise some 2500 m² of large-area formwork Top 50 and three concrete placing booms while situated here.
Gigantic cast in-situ concrete columns run up the outside of the structure, with a crane attached to each one for lifting in the rebar and speeding up construction workflow further.
The 400 m tall CMA Tower is characterised by its colossal nine-sided core, measuring over 40 m across the diagonal. Over
10000 m³ of concrete went into its foundations, and its dimensions remain unchanged from bottom to top, making its shaft core alone similar in size to a conventional skyscraper. Roughly 3000 m² of timber-beam formwork and 105 SKE100 automatic climbers have also been used.
It is hard to believe that the global fascination with skyscrapers is coming to an end, particularly after the Kingdom Tower was granted preliminary approval this year by the Kingdom Holding Company, headed by Prince Al-Waleed bin Talal Alsaud. The 1.6 km tall tower has been designed by Adam Smith, the same architect of the Burj Khalifa, which will be dwarfed by the new tower - making it the tallest building on earth upon completion.
The technology is clearly available, or if not it will adapt - as equipment manufacturers and contractors have been quick to demonstrate in the past. But surely there is a limit? This may be found in the risk to personal safety in cases of emergency evacuation.
In addition, the growing preference for sustainable building designs in Europe and the US may also begin to catch on in emerging markets, resulting in more use being made of wide expanses of land for horizontally building - allowing people to once more have their feet firmly on the ground.