Challenges in concrete construction...

By Chris Sleight10 May 2011

The twisting tower of the Absolute World City Center in Mississauga, Canada.

The twisting tower of the Absolute World City Center in Mississauga, Canada.

Increasingly complex designs, tight deadlines and higher tolerances are pushing equipment suppliers to develop more sophisticated, and more user-friendly products for the concrete construction sector.

Complex designs, be they for tower blocks or road layouts, make for challenging construction projects, and contractors are increasingly looking to equipment suppliers to help overcome not only the technical challenges they are presented with, but also demands for increased quality and fast construction cycles.

A good example of this type of partnership is the Absolute World City Center in Mississauga, Canada, where Peri has supplied its RCS climbing protection panel formwork system to the complicated build. The 170 m high south tower and 150 m north tower both twist as they climb, with constant rotation on the north tower, and varying changes between floors on the south tower, which makes for a complicated construction project.

Due to the different rotations by different degrees at different levels, Peri developed two unusual climbing methods from standard, modular components adapted to suit the project requirements and building geometry.

The 170 m Absolute Tower South has an elliptical ground plan and rotates by 208° over the course of its 56 floors, with twists of between 3° and 8° from storey to storey. During construction, Peri's RCS climbing panel completely encloses the uppermost three floors to ensure a safe environment, and the system also climbs independent of cranes, thanks to the company's hydraulic self-climbing system.

Construction of the 150 m high, 50-storey north tower began a few months after the south, and presented a slightly simpler challenge thanks to its constant 4° per floor twist. For this elliptical building, Peri designed a cost-effective variant of its RCS system.

The general contractor on the scheme is Dominus Construction from nearby Toronto, and the structural contractor, Premform Limited, is also from the same city.

In Rome meanwhile, two new high-rise developments are underway in the city's emerging Europarco business district. Currently under construction are the 110 m Europarco tower and the slightly larger 120 m Eurosky, which will be the city's tallest building when complete.

General contractor Parsitalia Costruzioni SRL is using a variety of Doka formwork on both towers, including SKE 50 and SKE 100 climbing systems and the company's Xclimb 60 protective screen. Previous projects in Italy to use Doka systems have included the 160 m Palazzo Lombardi in Milan, Bologna's 125 m Torre Unifimm in Bologna and the tallest building in Italy, the 165 m Intesa San Paolo high-rise in Turin.

Building in the other direction meanwhile, Constructora Internacional chose Efco formwork for its work on the extension of Line 5 of the metro system in Santiago, Chile. The company's contract to build the underground Estacion Del Sol - one of seven stations on the extension - required a formwork supplier that could provide a range of solutions, durable formwork that would provide a high quality finish as well as technical assistance with erection and assembly drawings.

A combination of Efco's Hand-E-Form and Super Stud forms were used for one-sided walls, while its Plate Girder system was employed for the columns and E-Z Deck for the slabs. Construction of the station began some 17 m below ground, and it consists of three levels with a combined floor area of 10000 m2.

A particularly difficult area was the construction of two parts of the mezzanine level, where the slab forms could not be supported directly from the railway level. For these areas, Efco designed special structures combining E-Z Deck towers and Plate Girder panels to span the railway.

In Germany meanwhile, Meva supplied its KLK 230 climbing formwork to the renovation of the Klingenberg dam, which was built in 1914 and damaged during the floods of 2002.

The company's engineers designed and constructed a special adapter beam that could be mounted to anchors set into the dam. The curve of the face meant that the anchors were not always parallel, so the beam had to be able to cope with these tolerances.

The work involved sealing the dam's upstream face and installing new drainage systems. This meant adding four layers of material, a 400 mm to 800 mm layer of concrete to even out the stone surface, followed by a bitumen foil to allow this equalising layer to move independently of the sealing layer. This was then followed by a 130 mm thick course of hollow drainage bricks, and then a 400 mm thick layer of sealing concrete.

"Thanks to the special design of the climbing formwork units, we were able to work in parallel and perform several jobs at the same. This has enabled us to precisely control and fine-tune all work steps during the complex renovation," said site manager Marko Würker of main contractor Züblin.

In Oman, meanwhile, one of the elements of the € 2.6 billion (US$ 3.8 billion) new iron ore processing plant in Suhar is a 35 m high, 16.4 m diameter storage tower, with walls from 1.5 m thick at the base to 1 m at the top.

Main contractor Galfar Engineering & Controlling used Paschal's TTR circular trapezoidal girder formwork for this challenge. The climbing system allowed the tower to be constructed in 12 3 m pours. Due to temperatures of over 40° C during the day, concreting work was only carried out at night.

Paving

But it is not just in high rise construction that concrete equipment manufacturers are being challenged. In Australia, a road safety project called for an unusually large concrete barrier to be slipformed at the bottom of the winding Bulli Pass near Sydney.

Concerned with the potential for trucks to lose control at the bottom of the road, the local authority decided on a 2 m high wall, anchored to a 1 m x 1 m footing, resting on 8 m deep piles. Main contractor BMD Construction sub-contracted the work to Nation Wide Slipforming, which used its Power Curber 5700-C-MAX to get the job done quickly and minimise the disruption from road closures.

Construction Manager Warren Scattergood used the C-MAX's low speed torque hubs to crawl the machine at 300 mm to 400 mm per minute, allowing for the necessary concrete compaction and vibration in the behemoth mold. "Even with the auger at full speed, a 3500 kg mold attached, and running all nine vibrators I had plenty of horsepower" noted Mr Scattergood. "I checked the engine stats while paving and was running at 70% of capacity."

In the US meanwhile, Iowa-based paving contractor Manatt's used its 2004 model GHP-2800 Gomaco slipform paver with a new 5400 series mold and bar inserter for a 12.5 mile (20.1 km) stretch of Highway 30 in Iowa. The company also upgraded to a G22 controller and new software to help ensure it met the state's exacting requirements for surface smoothness.

Two pan-mounted Gomaco Smoothness Indicator (GSI) units were used to monitor the paving results, which were recorded on the G22. After three days, with the help of Gomaco engineers, the software and paver were fine tuned.

Mannatt's paving superintendent, Kevin Hogan said, "We always have different variables popping up while we pave, from temperature variations, concrete slump changes, to everything else. The new G22 and the GSI work together to help us overcome those variables and solve any problems immediately. It's a huge asset for a contractor to have.

"Before, if we were getting questionable numbers, we didn't know until 24 hours later when the ride report was output from the profilograph readings. Now, the GSI is constantly tracing throughout the day and alerts us to any imperfections. It eliminates a lot of guesswork."

Wirtgen meanwhile has launched its Autopilot 3D control system for its SP 15 and SP 25 slipform pavers. The company says this machine control system is user-friendly and cost-effective, while guaranteeing high precision and efficiency, regardless of whether straight profiles, highly complex curved profile paths, or even closed profile configurations need to be paved.

The system comprises a computer integrated in the machine as well as a control panel that allows intuitive operation. Two GPS receivers, which are mounted on masts on the machine, communicate with an additional GPS reference station positioned on site. The machine control software is a proprietary Wirtgen development.

Wirtgen says programming the system takes just a few minutes. All the operator has to do its select a profile configuration, length, width and radius. This establishes the paver's steering configuration. A starting point is then specified, followed by an elevation profile and any cross-slope. Laser and ultrasound sensors are then used to scan the ground to make sure everything is level before paving begins.

Pumping & placing

August saw Putzmeister called in to provide equipment to construct a narrow motorway junction where the A9 and the A92 meet north of Munich, Germany. The job, which is due for completion this October, demanded the maximum reach of some of the company's largest placing booms.

Two large Putzmeister boom concrete pumps, the M 58-5 and M 62-6, were drafted in by contractor Hentschke Bau to help with replacing the current, single-lane exit with a flyover that channels a two-lane carriageway from the A92 to the A9 towards the south.

For the first 120 m section of the flyover, a total of 2000 m3 of concrete was placed over a 24 hour period - enough for the entire cross-section of the structure.

The second section - a road segment that is 80 m long - will be completed later this year and the complete superstructure will contain 2300 m3 of concrete.

The high level of flexibility of the machines' booms were key criteria in their selection for the task - Putzmeister claims the

M 62-6 and the M 58-5 have the longest horizontal reach of any pump in the wider Bavaria region. The M 58-5 features a five section RZ folding boom with a maximum vertical reach of

57,6 m, while the larger M 62-6 features a six section RZ boom with a total vertical reach of 61,1 m.

Each of the two truck-mounted concrete pumps used the full extent of their horizontal reach in order to pump concrete to the 12 m-high placement site. All the while, traffic was flowing freely on the circular paths of the exits and under the structure.

New booms

Zoomlion has been unveiling new models for key export markets this year. For example, March's Samoter exhibition in Verona saw it unveil a new 33 m truck-mounted concrete pump targeted at Europe. The Zl33 is a Z-fold unit produced in China and Assembled by Zoomlion's Italian subsidiary Cifa, which offers parts and services for both the Cifa and Zoomlion ranges via its dealer network.

April's Kommatek show in Turkey meanwhile saw the company unveil the 37 m 37X-4Z, mounted on a Volvo chassis. Again, it is a Z-folding boom, offering 120 m3/hour of output and pressures up to 70 bar - the same characteristics as the ZI33.

Sany, too, presented new equipment at the Samoter exhibition. The Chinese manufacturer revealed its first 30 m class RZ five-section concrete placing boom.

Coupled with a SYG 5260 truck-mounted concrete pump, the boom can be mounted to standard three-axle chassis as well as four-axle trucks with wheel bases as narrow as 2.3 m. Sany has also redesigned the boom's self-supporting, stress-free sub-frame with X-shaped outriggers in front, and straight outriggers in the rear.

Added value

These case studies and new equipment launches go to show how manufacturers are rising to the challenge presented to them by contractors and construction clients alike. It is not just about the equipment, but also the services and support that leaders in the field can provide when particularly difficult projects come up.

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