High-rise construction - reaching for the sky
By Chris Sleight09 September 2015
The last decade or so has seen the construction of high-rise buildings take a leap forward, or maybe upwards. The defining project has been the 828 m tall Burj Khalifa in Dubai, UAE, which smashed all previous records for tall structures. It opened at the start of 2010 after a six-year construction period.
But even that achievement looks likely to be eclipsed in the coming years, as the Kingdom Tower rises from the ground outside Jeddah, Saudi Arabia, to its eventual height of 1 km. Completion is due in 2019.
The striking thing about these towers is how much taller they are than the previous generation of skyscrapers, competed in the late 1990s and early 2000s. At just over 500 m, Taipei 101 in the Taiwanese capital was the tallest building in the world when it opened in 2004, but just 15 years later a building almost twice its height is moving towards completion.
So what has happened in the intervening years to allow the construction of buildings so much taller than their predecessors? To find out, iC spoke to Dr Andy Davids, global director of tall buildings at consultant Aurecon, who has worked on numerous high-rise schemes, including the Burj Khalifa.
Dr Davids said, “The big advance on Burj Khalifa was the use of a hexagonal core which reinforces the three buttresses that form the distinct Y-shaped cross-section of the building. The hexagonal core offers better lateral strength, and many future super-tall building will replicate this in their designs.
“In more practical terms, the introduction of technologies such as double-deck elevators, which comprise unconnected cabins operating within the same lift shaft, allow for the movement of greater numbers of people efficiently which is necessary in super-tall buildings.
“From an engineering and construction standpoint, the use of modern materials that can withstand extreme weather, primarily the heat and the wind shear forces, has been important. The high strength concrete used in the job was not only resistant to the conditions but it also meant minimal rebar was required.
“In terms of equipment, the project made use of high pressure concrete pumps capable of delivering poured concrete at up to 200 storeys and tower cranes with the capacity, rope length and design to reach the required height.”
So what will be the limiting factors for the height of buildings in the future?
“The most significant limit is the attention span of the owner,” said Dr Davids. “Burj Khalifa took seven years to design and build before the owner began to see a return on investment. It’s unlikely that owners would wait much longer than say, 12 years, certainly not 15 years. So the real question then becomes, how high can I build in 12 years?”
Speed of construction
Clearly this is an area where advances in construction techniques and materials could contribute.
“A reliable speed of construction is crucial and we need to keep simplifying the typical daily construction activity,” said Dr Davids. “Development of a concrete-like material which did not need complex reinforcement would be a great help, as would increasing the grade of concrete to reduce the volume of material required each day.
“One solution to this might be in modularisation. In China there is a company working on a modular design and construction for an entire super-tall building, while at Aurecon we’re working with developers on plans where super-tall buildings can be constructed in stages, making them flexible to change in use, especially during construction. This will make them more viable over a longer term.”
But while modularisation might make a contribution, Dr Davids warned the time and cost savings promised by those at the forefront of this technology should not be taken at face value. Construction time on site might be shorter, but there is the addition of the manufacturing time for the construction modules themselves.
These techniques might be something for the future, but at present, the world’s tall buildings are being built by traditional means. On the 1,000 m, 240 floor Kingdom Tower for example, Doka has provided formwork, Liebherr the tower cranes and Schwing the concrete equipment.
Offering 530,000 m2 of floor space, the tower will be divided into two parts. The Residential Tower comprising 167 floors up to a height of 674 m will be followed by the ‘Spire’ between floors 168 to 240. This will take it to a height of 962 m, and the structure will be reinforced concrete. The final 40 m or so will be a steel pinnacle.
The main contractor, Saudi Binladin Group, chose Schwing Stetter as the concrete equipment supplier. The machinery supplied to the project includes two Stetter HN 3.0 batching plants to produce the concrete on site, along with four Schwing SP 8800 D stationary concrete pumps. These have an engine power of 450 kW each and a maximum feed pressure of up to 243 bar.
A high-performance, C85 self-compacting concrete will be used for construction up to a height of about 400 m, and a sophisticated on-site trial had to be carried out to ensure the pumpability of the mix. The next construction phase will extend up to a height of 675 m and will also be carried out with a high-performance concrete, but with a lower compressive strength. At the top of the second construction phase, a concrete pump will be installed for subsequent project stages, to transport concrete to the higher floors.
Schwing has also supplied five concrete placing booms – three SPB 35s and two SPB 30s booms, and the company’s order also includes over 1,000 m of pumping line for the first construction phase up to 200 m.
Meanwhile in New York, US, Manitowoc supplied a Potain MR 415 tower crane to the iconic 432 Park Avenue development. At 1,396 ft (425m) this strikingly slender structure is the tallest residential building in the world, although it will be overtaken by the Kingdom Tower in a few years.
As Tony Rodrigues of lifting contractor Roger & Sons Concrete explained, the company wanted to make use of the MR 415’s electric power and high line speeds that can hit speeds approaching 900 ft (275 m) per minute.
“When you’re picking loads off of an NYC street and lifting them 700 ft (210 m) or more in the air, a quick line speed and sturdy winch can really cut down on the amount of time spent on the job,” he said. “Since the construction was scheduled around the crane’s ability to lift, this meant the entire project was completed sooner.”
Near the completion of the project, the MR 415 was some 1,500 ft (455 m) above the street. At that time, line speed became crucial to the success of the project. When working with a single fall of wire rope, the on-board 215 LBR 120 winch can lift loads of 2.4 tonnes at speeds of 840 ft (256 m) per minute. Another useful feature is the winch’s ability to accommodate up to 1,903 ft (580 m) of rope on the drum.
The building has a 90 x 90 ft (27.5 x 27.5 m) footprint from base to roof. It was constructed “Chicago Style,” meaning without a façade or solid walls. The frame was built in concreted columns, to which windows were popped in. It was constructed on the former site of the famed Drake Hotel, which was demolished to make way for new development.
San Francisco skyscraper
Meanwhile in San Francisco, US, Wolff has supplied a
700 B luffing jib tower crane to the 181 Freemont Street project, a 244 m skyscraper.
The project required a crane with high lifting capacities covering a wide working radius and fast line speeds, while at the same time being as space-saving as possible. Lifting contractor Maxim Crane Works opted for the Wolff model, which has a lifting capacity of 50 tonnes, or 16.5 tonnes at a 50 m radius, and which offers a 190 m per minute line speed. Another plus was its compact footprint – it stands on a 2.3 m square tower section.
The Thai capital Bangkok is also a hotbed of high-rise construction at the moment, as evidenced by a series of prestigious projects. Liebherr has had a successful year, supplying tower cranes to the Thai Parliament building project and a further four to the construction of the new Supreme Court.
The new Supreme Court, along with an office for the Courts of Justice, is being built on the site of the earlier Supreme Court complex that had been built in phases, starting from the early 1940s and ending in 1963, in Bangkok’s Rattanakosin conservation area.
Tight restrictions are placed on any building projects in the district, and the only type of tower crane allowed for the new Supreme Court was a luffing jib model, to ensure the crane booms do not overfly the Sanam Luang ceremonial ground in front of the site, or the city moat behind the building.
Two Liebherr 125 HC-L 6/12 Litronic cranes are being used on the project along with two 112 HC-L units by contractor Sino-Thai Engineering.
“These four cranes were previously used by Sino-Thai on a four-storey hospital project in Bangkok, where the footprint of the building was large, and stringent no-overfly restrictions prevailed,” said Chupak Jirarojveerakul, Sino-Thai’s project manager at the Supreme Court.
The 125 HC-L has a maximum lift of 12 tonnes and a 50 m jib that can be angled anywhere between 15° and 70° and slew through 360° under load at only 7 m slewing radius. The 112 HC-L has the same jib angles and slewing ability, with a 45 m jib that can also lift a maximum load of 12 tonnes.
Elsewhere in the city, Linden Comansa supplied two tower cranes to the construction of the MahaNakhon tower, which at 314 m and 77 floors is the tallest building in Thailand.
A luffing jib LCL310 24 tonne capacity model has been on site at the base of the tower since 2012, and is used for unloading and distributing supplies.
A more recent addition to the site was the 21LC290 flat-top 18 tonne capacity model at the top of the tower, which was fitted with a 40 m jib. This features Linden Comansa’s internal climbing system, which is tied to the structure of the building. This allows the crane to climb quickly and safely while maintaining two ties to the structure. The manufacturer said it also saves money as it only needs 11 mast sections, while a external crane would need more than 60 mast sections to reach the height of 340 m.
Across the Pacific in Hawaii, the 45 storey Symphony Honolulu is rising to a height of 400 ft (122 m) to be the island’s tallest building. Putzmesiter supplied concrete contractor Ohana Concrete Pumping with 43 m and 47 m reach truck-mounted placing booms for the complex foundation construction phase, as reaches of up to 46 m were required on the 82 x 84 m footprint of the concert hall and residential tower.
Following that, the first three floors were pumped using truck-mounted boom pumps before a detachable 38 m placing boom was installed on the self-climbing formwork to take over concrete placement.
Tim Rippy, superintendent for Honolulu-based general contractor Nordic PCL Construction said, “We selected this new system because of its self-jacking formwork that meant we didn’t need a crane to climb.”
Joe Frederick, operations manager at Ohana, added, “We supplied the cross frame to Nordic who mounted it, which is an easy process as it only requires four long bolts. Now that the new system is in place and the tower rising, it means one less step for us, as we don’t have to jack up the placing boom tower for each level. We just show up and start pumping concrete.”
Climbing in Sydney
In another application of self-climbing formwork, Peri has supplied its LPS climbing protection panel system to the Barangaroo Redevelopment Project’s International Towers Sydney (ITS) structure in Sydney, Australia. The ITS high-rise complex consists of three towers with 39, 43 and 49 storeys, the tallest of which will be 217 m.
Peri designed the formwork and safety solution around the LPS self-climbing system to provide protection against falling as well as weather conditions in the work area. The girder grid units can telescope to adapt to the changing floor plan, while foldable covers at the base of the climbing protection panel provide safe working conditions in the areas below. The Peri system also accommodates ceiling heights which vary between 3.8 and 5.5 m.
LPS stands for Light Protection Screen and Peri describes it as a weight-saving alternative to conventional, closed enclosures. It is similar to the company’s rail climbing system (RCS) as it also self-climbs
There is a similar safety requirement for Bouygues subsidiary Dragages Macau on the construction of the City of Dreams project in Macau. All of the formwork climbing units must be able to withstand the force of a typhoon wind reaching 250 km/h. In addition, the perimeter walls are being erected in
a manner that does not disturb the hotel which next door.
In order to avoid any noise transfer via contact, the Meva Guided Climbing (MGC) formwork was modified to allow the platforms to carry both sides of the formwork for the 1 m thick walls. Gallow suspension, formwork connections and climbing on complex geometries were custom designed.
The Meva Automatic Climbing (MAC) system on the project provides formwork for the core and the walls in one, which makes for faster cycle times. The company’s heavy duty Mammut 350 formwork was used on the project to accommodate the high pressures from the self-compacting concrete.
This illustrates that innovation form construction equipment suppliers is not only making even taller buildings possible,
but also improving safety and productivity into the bargain.