Two Liebherr luffing jib cranes construct Latin America's tallest tower

Project owner Cencosud has purchased 12 of the total of 14 cranes on the site from Liebherr's distributor in Chile, Maquinarias Cruz del Sur SA (MCS), while MCS's rental division is supplying the other two units.

The US$ 500 million Costanera Center is being built in the Central Business District of Santiago, opposite the World Trade Center, construction having begun in 2006. There are four towers to the project, the tallest of which is the Torre Gran Costanera, designed by César Pelli, which at 300 m will have 70 floors, making it the tallest building in South America.

Also involved in the design of the Torre Gran are Chilean architects Alemparte Barreda y Asociados and Canadian company Watt International. Structural engineering is being undertaken by the Chilean company René Lagos y Asociados Ing Civiles Ltda.

Two of the projects towers, Costanera 1 and Costanera 3, are both 41 storeys in height, measuring 170 m (558ft), while the Costanera Hotel tower is 25 storeys, measuring 105 m (344ft). The Costanera Mall will be five storeys, at a height of 30 m (98ft).

Within the project will be two hotels, one four-star and the other five-star, two department stores, office accommodation, and a shopping mall with more than 300 stores and a food court.

Project director Bernado Hopp says the decision to use only Liebherr cranes on the project was made by Cencosud after lengthy discussions with Liebherr and MCS; during which engineers from Germany visited Santiago several times and together with MCS engineers, made suggested modifications to the project, which will have a total constructed area of 694,000 sq m, to maximise the tower crane deployment.

Initially, Cencosud had considered using three tower cranes for the Torre Gran Costanera, but Liebherr demonstrated that with correct deployment, two cranes could be just as effective, thereby saving the owner the cost of a third crane.

Hopp says that the joint decision to use Liebherr HC-L luffing jib cranes for the highest tower was made to save crane space. The short counter-jibs of the cranes take up far less space than the more conventional flat-top or hammerhead crane design, allowing the cranes to work freely through 360 degrees without the risk of obstructing other crane jibs on the site.

Their small slewing radii and raised jib angles of 15 to 70 degrees, even when not in operation, make these cranes particularly advantageous in operations on tight sites containing numerous cranes with overlapping slewing areas.

Both the luffing jib units are Liebherr type HC-L models. One crane, a 335HC-L, has been anchored to the outside of the tower and will climb all the way up to the maximum building height of 300 m. This unit has a 55 m jib with 5,500 kg tip load, and a maximum hoist speed of 170 mts/min.

The second, a model 224HC-L, has been located inside the building in the elevator shaft, and will also be used to the full height of the tower, after which it will be dismantled and removed by the 335HC-L. This second crane also has a jib length of 55 m, and has a tip load of 3,200 kg. Maximum hoist speed is 240mts/min.

Floors 1 to 10 of the Torre Gran will have a floor-to-floor height of 6 m, while floors 11 to 60 will have a floor-to-floor height of 4.1 m.

Hopp says that the speed at which the cranes can lift heavy loads was a vital factor on a project this size, because a crane with even a slightly slower lift speed or lower lift capacity would eventually lead to a much longer construction period on such a tall tower.

Lifting speeds and jib lengths were important factors in selecting the cranes for the other elements of this complex project, unit specifications having been matched carefully to the required construction cycles by Liebherr and MCS engineers.

Seven of the Liebherr tower cranes are top-slewing types, designed to give an exceptionally high load capacity at full reach. Three cranes purchased by Cencosud are 200EC-H10 Litronic models, with a jib length of 60 m a tip load capacity of 2,650 kg and a maximum hoist speed of 100 m/min.

Two are model type 200EC-H10, with a 55 m jib length and 2,850 kg tip load, and a 100 m/min hoist speed.

The two remaining top-slewing cranes are model types 154EC-H10, one equipped with a 55 m jib and the other a 60 m jib, with 1,850 and 1,400 kg tip load respectively. Both units have a maximum hoist speed of 100 m/min.

The three other cranes belonging to Cencosud are flat-top design, whose compact head incorporates the hoist gear, the slewing gear, the central switchgear and the complete ball-slewing ring support.

Quick-release fastenings make pinning the jib and counter-jib considerably easier, and the cab can likewise be attached and removed using quick-release fastenings. These three units are all model type 90EC-B6, with a jib length of 50 m and a 1,500kg tip load. These units have a 70 m/min maximum hoist speed.

One of the two Liebherr cranes supplied by the MCS Rental Fleet is also flat-top unit, a model 99EC with a 50m jib, 1,600 kg tip load and a 103 m/min maximum hoist speed. The second rental unit is a top-slewing 98.3HC with a 50m jib, 1,500 kg at tip, and a 114 m/min hoist speed.

Chief executive officer of MCS Raul Montt says that the two rented units are being deployed on the shopping mall construction, which will be the first element in the project to be completed. As soon as the construction work is done, they will be removed.

Montt says that a buy-back option has been included in the contract for the 12 cranes purchased by Cencosud. If this option is taken up after the project is completed, the probability is that the two luffing jib cranes, whose size would give them a very limited market in Chile, would be re-exported. The other 10 units would join the MCS fleet.

MCS is providing an on-site operating and maintenance team of 25 people, and Montt says that the longest unscheduled shutdown of a crane would be no more than 45 minutes.

Routine maintenance on the cables, pulleys, gears and other moving parts is undertaken every 200 hours, when the cranes are stopped for a period of four hours. The aim, says Montt, is to ensure that the cranes are continually functioning at 100 percent efficiency on this very complex and prestigious site.

Montt adds that MCS has developed an emergency service to rescue a crane operator or service engineer should he find himself in any kind of difficulty. This was initiated early last year on the advice of Liebherr, who recommended the system developed by the Austrian company, Save A Life (SAL), in which a safety harness is used to bring the operator to the ground.

MCS, which has now assimilated this system into its operating manual, has actually had one instance on a different project last year, when an operator suffered from dizziness and fainting while working at a height of 36 m. A three-man MCS rescue team, using the SAL system, had climbed swiftly to the crane cab and strapped the operator into the safety harness, bringing him safely to the ground so quickly that the city fire service was still in the process of erecting its ladders.

MCS has been Liebherr's distributor in Chile only since 2003, when the company was founded with just 27 cranes in its rental fleet and a staff of 30 people. Chile's burgeoning construction sector has resulted in rapid growth, and MCS now has more than 100 cranes and a total of 240 people.

Montt says that previous to the Costanera Center, the largest project that MCS had worked on was the new Santiago Justice Center, which used 13 cranes and which was completed in 2005.

"We built our reputation on that project," he says, "The Costanera Center is going to be very much a learning experience for everyone involved, and of course, everyone is determined that it will be a great showpiece of a project."