The only way is up

Despite the tragedy of the 9/11 attacks and the collapse of Madrid's Torre Windsor following a fire in February this year, tall buildings are as popular as ever. Richard High reports on the latest equipment available, the techniques used, and some of the projects currently taking place and in the pipeline.

In Dubai, United Arab Emirates (UAE) last year, according to the UK's Chartered Institute of Building, there were over 343 multi—storey buildings under construction.

King of the iconic high—rise buildings currently emerging from the sands of Dubai is property developer Emaar's Burj Dubai Tower (see this month's site report). Designed by Skidmore Owings and Merrill (SOM), the Burj will be at least 800 m tall, although Emaar is keeping the final height a secret.

In the US, SOM is currently involved in the re—design of the 1776 ft (541 m) high Freedom Tower, which will be the centre piece of the new World Trade Center. It has also signed letters of intent with Moscow's construction chief Vladimir Resin to jointly design skyscrapers in the city.

The city is currently undergoing something of a renaissance in high—rise development. The US$ 12 billion Moskva—City project, for example, will see several towers built, including the 85 and 57—storey Federation Towers (see IC July—August 2005), the Eric van Egeraat designed US$ 250 million Gorod Stolits (The City of Capitals) towers (62 and 73 storeys), the 116—storey, 648 m Russia Tower and the 265 m Triumf Palas.

The Dutch architect has also designed the US$ 175 million Russian Avant—Garde residential complex. It features five towers, from 10 to 17—storeys, named after 20th century avant garde painters — Kandinsky, Malevich, Rodchenko, Popova and Exter.

Seismic design

In Beijing, SOM, in partnership with Wong Tung, is the architect of Phase Three of the China World Trade Center (CWTC), part of a long—term project in the city's Central Business District. Ground breaking took place in July this year and completion is expected in 2007.

The centrepiece is a new 330 m tower that will become the tallest building in Beijing. It will feature office accommodation, a five—star hotel at the top, and retail and entertainment venues.

Structural engineer Arup faced a huge challenge in proving that the new tower would be able to withstand the high seismic design intensity (Intensity VIII) in the area, as the height and the scale of the tower go well beyond the limits of previous structures in the city.

“The project team undertook an intense period of analysis to prove to the client that the building was robust. They developed new analysis methods that included non—linear time—history analysis. This has provoked a great deal of interest in the Beijing planning community as such comprehensive tests have never been undertaken before,” said a company spokesman.

Arup studied the feasibility and cost—effectiveness of a number of structural systems. Structural steel perimeter frames, together with a central braced service core, were chosen as the main lateral system, which will be combined with concrete for the lower portion of the building.

Also mooted for construction in Guangzhou is a Richard Rogers Partnership (RRP) designed sightseeing/television tower. RRP's design is 475 m tall and sits on the southern bank of the Pearl River, while two 350 m towers sit on the opposite bank. At the top of the tower is an oval glass ‘eye’ that will give panoramic views of the city.

“Already in the preparatory phase, PERI offered the best formwork concept. We chose PERI due to its experience with climbing form—work and the excellent formwork systems. During the construction phase, we had great support from PERI Netherlands. The core was climbed in weekly cycles and slab forming with PERI SKYDECK and UNIPORTAL tables functioned well.”

Main contractor TNSS Consortium is using four Kroll K—320 tower cranes during construction of the ‘Mega Bridge’ contract, part of the 13 km long Industrial Ring Road, Bangkok, Thailand. The cranes are being used to transport materials and Peri formwork up the bridge pylons.

US expansion

In the US, construction has begun in New York on the Durst Organization and Bank of America's 195000 m²,54—storey, 945 ft (288 m) high Bank of America Tower at One Bryant Park. Ground breaking took place in August 2004 and completion is due in 2008.

The US$ 1 billion glass, steel and aluminium skyscraper is inspired by the city's Crystal Palace, the first glass and steel building in America, erected in Bryant Park in 1853. What will make this building different from any other in the US, however, is that Cook+Fox has designed it to be an “environmentally responsible”building.

Also in New York is the Santiago Calatrava designed 80 South Street Tower, the first residential building he has designed in the US (see IC September 2004). Other US—based projects currently under construction include the Daniel Libeskind designed, US$ 40 million, 300 ft (92 m) high Ascent at Roebling's Bridge on the banks of the Ohio River.

Mr Calatrava has also proposed a residential tower design for Chicago's lakefront that could become the tallest building in the US. The 115—storey glass and metal—clad building, dubbed the Fordham Spire, spirals at 2° per floor to its rooftop mast, which is included in the building height of 2000 ft (610 m).

Discounting the mast, the building's roof is actually 1458 ft (444 m), just 8 ft (2.4 m) taller than the current record holder, the nearby Sears Tower.

Tight schedules

Also in the US, and currently under construction, is a new 122 m hotel tower on the Palms Casino &Hotel site in Las Vegas. The expansion includes a new hotel and bigger casino located on a 13 ha site.

Construction of the new 30—storey hotel tower started in mid 2004 and is expected to finish later this year.

Like many high—rise developments in the area, and there are currently an estimated 80 towers either in construction or in the planning stages in Las Vegas, it is constrained by a tight construction schedule.

To meet this challenge, the project was commissioned in phases with very short construction times. To help meet these tough time demands main contractor Isaac Construction turned to Conesco Doka for use of its self—climbing formwork systems.

“In Las Vegas it's all about speed,” said Jack Oldfield, senior account manager at Doka. “Therefore we recommended three key Doka formwork systems to Isaac Construction; the SKE 100 automatic climbers, Top 50 large—area formwork and Framax column forms.”

Doka has had equipment on site since work started on the substructure of the building in September 2004. Its Framax system, which was chosen, according to Mr Oldfield, for speed of assembly and versatility, was used on the first lift of the core. The SKE automatic climbing system was then used in conjunction with Doka's Top 50 formwork for the core projects.

Main contractor Taisei Corporation of Japan is currently conducting pile load tests at property developer Nakheel's Al Mas Tower, Dubai. The 350 m high, 65—storey, 160000 m² tower includes a four level basement with parking for 1700 cars. Part of the Jumeirah Lakes development it will be the focal point of the Dubai Metals and Commodity Centre. It will house the region's only diamond exchange — the Dubai Diamond Exchange (Almas means ‘diamond’ in Arabic). Construction is scheduled to finish in 2007. Faithful &Gould is the project manager and WS Atkins & Partners is the consultant.

Space on—site is extremely restricted. According to Mr Oldfield, it is one of the most cramped workplaces he has ever worked in. The very small footprint posed several challenges, particularly at the start of the project.

“Electrical power lines very close to the new building meant we had to prepare the formwork sub—assemblies just outside the building area and then slide them under the power line close to the building where they could be positioned by tower crane,” he said.

One of several challenging aspects of the formwork is that one third of the columns are of different sizes. The Framax system's flexibility, said Mr Oldfield, means the different sizes can be handled without applying different modules.

Unusual core

The core of the tower contains two sections with four elevator shafts, with three elevators in each shaft. Both sections standing at an angle to each other and together with the walls form an unusual shaped core.

Construction uses Doka's Top 50 formwork system, which is designed to accommodate a 4.3 m floor—to—floor height, mainly for the upper floor suites in the new hotel tower. For the lower floors, the same Doka ganged wall forms are being used, but are only poured with concrete to the specified height for the lower floors 3 m floor—to—floor height.

Not having to change the ganged wall forms simplifies the work, speeds up production and saves money, said Mr Oldfield.

Fourteen SKE 100 self—climbers are used at the core and six at the staircase to lift the formwork. Most of the steel superstructure frames for the gantry style self—climbing SKE systems are out of sight, hidden within the elevator shafts.

“After the floor has been poured in the morning, it is left for approximately six hours to settle, after which the core is poured. The formwork is then stripped and lifted during the night. The system is very user friendly,” explained Rex Taylor, assistant superintendent at Isaac Contractors. “When we started, it took us eight hours to strip and climb. Now we can do it in four—and—a—half hours.”

Materials handling

Of course construction of any high—rise project would not be possible without efficient materials handling, and hoists and tower cranes are the most obvious ways to transport material around a site. A fixed, or saddle jib is the “normal”tower crane configuration for most projects, however, if the site is cramped a luffing jib configuration is more suitable.

In the heart of Dubai's Sheik Zayed Road, for example, two Liebherr 112HC—L luffing jib cranes are providing lifting power for the 42—storey Golden Sands

Tower. The compact site is ‘wedged’ between two existing high—rise towers; posing severe space restrictions on crane configurations.

Main contractor Al Shafar General Contracting opted for a luffing jib crane following experience with its two 112HC—L's on the Jumeirah Beach Residence Sector 6 Project, which also experienced similar cramped conditions.

The 112HC—L is designed specifically for sites with restricted space. With the steep luffing jib angle (15º to 70º) it is able to avoid on—site obstruction with other working areas and slew through 360º under load. A slewing radius of just 7 m is also possible, which makes it ideal where several cranes have overlapping slewing radii.

Both cranes will climb within the building's concrete pouring cycle, with one floor being completed each week.

The cranes are ‘jacked—up’ toThe Eric van Egeraat designed US$ 250 million Gorod Stolits (The City of Capitals) consists of two towers, 63 and 73 storeys respectively, which symbolise Moscow and St. Petersburg.

Work on the 42—storey residential Golden Sands Tower is scheduled for completion by 2006 and will be clad in curtain walling.

Lack of space also influenced the choice of tower crane configuration in Bangkok, Thailand. However, this time it was space on the ground for a new road. To overcome this the city's transport authorities designed the new 13 km long Industrial Ring Road (IRR) so parts of it will be 50 m above the surrounding area.

As part of the ‘Mega Bridge’ contract, main contractor TNSS Consortium (Taisei, Nishimatsu, NKK and Sino Thai) turned to Kroll Cranes for a solution to the material handling duties at the site. Kroll supplied four K—320 tower cranes for the project, which comprises two cable—stayed bridges with lengths of 702 m and 582 m.

Both bridges, with main spans of 326 m and 398 m respectively, are supported by two pylons each. These are designed to form a diamond shape, with heights of 173 m and 164 m. As the pylons rise from the city below, so do the tower cranes. Topping out the pylons will mean jacking up the cranes as construction progresses, giving a final height under hook of 186 m. Maximum lift at 63.4 m is 4.3 tonnes, or 18 tonnes at 19 m.

Windy city blues

Sub—contractor Goebel Concrete Forming Inc. has used Meva's Imperial wall formwork system in combination with its KLK climbing system, during construction of the 21 storey, 250 ft (76 m) high Grand Orleans Condominium, Chicago, US.

The Condominium's lower seven levels provide parking space for about 110 cars. On top of this are 14 storeys of condominiums, seven per floor. The entire perimeter walls were formed using 8’ by 1.5’ (2.44 by 0.46 m) panels to reach the wall height of 9.5’ (2.90 m).

Innovative solution

Another innovative solution to cramped site conditions, and a tight construction schedule, was provided by formwork manufacturer Peri, working in close cooperation with maincontractor Sorbara Construction Corporation (SCC) at the World Trade Center, New York, US.

Currently under construction in direct proximity to the Ground Zero Memorial Site, 7 World Trade Center (7WTC) is the first high—rise building to be erected as part of the WTC master plan. It will reach a height of around 210 m and provide almost 158000 m² of space on 52 storeys.

Since the attacks of 9/11, escape and rescue from multi—storeyed buildings in emergency situations has been the subject of much discussion. Developer Silverstein Properties insisted on building standards that would provide the highest possible level of fire resistance and safety against a terrorist attack.

In order to meet these requirements, the first 25 m of the building is designed with massively reinforced concrete. Over this, there is a 29.23 x 21.26 m reinforced concrete core, which forms the “load—bearing backbone”of the whole construction. The storey slabs and external walls are formed using a steel framework.

SCC is responsible for the concreting work and it has worked closely with Peri in the planning, design and delivery of a suitable formwork solution.

The rectangular reinforced concrete core of the 7 WTC contains six — in the ground plan — almost square—shaped shafts, which are separated by a connecting passage. Internal wall thicknesses are 250, 360 and 440 mm, with 690 mm thick longitudinal external walls. Depending on the floor, up to 30 lifts are accommodated in the shafts. Using its ACS—P (platform) self—climbing formwork as a base unit, Peri's engineers designed a 76 m² platform for each of the six shafts. Only two crossbeams are required to hold each platform, which can be independently climbed.

The ACS 100 climbing system is the central element. It allows crane—independent climbing and its large—volume 100 kN lifting power provides a high degree of safety. The platforms are controlled via a total of six four—fold hydraulic pumps.

During the construction process all of the steel components for the reinforced concrete core are placed in advance. During the design of the wall formwork operations this presented some physical problems, not least a limited space of just 500 mm when striking the Peri Vario external wall formwork.

The formwork also has to be raised as the reinforcement is brought in from outside using electric chain hoists, which are attached to specially designed gallows. Peri's engineers positioned these on the elevated working platforms on level +1.

However, with the steel structure running through the entire core, the formwork for the area where the reinforced concrete and steel structure meet, had to be designed with low dead weight. This, it was discovered, was the only way for the construction crews to efficiently carry out forming manually.

The formwork design allows completion of a single storey in a four—day cycle with concreting taking place every two days.