Designed to withstand avalanches and wind speeds up to 220 km/h, two free-standing Wolff tower cranes will be fully erected on high mountain operation sites in the next four years.
The Swiss energy company Kraftwerke Oberhasli (KWO) has commissioned the Swiss construction company Arge Grimsel to replace the Spitallamm Dam on the Grimsel Lake near Grimsel Pass in the Canton of Bern, Switzerland.
The existing dam wall is about 90 years old and will be replaced by a new dam wall by 2025. The old wall must first be renovated. Once the new wall is built, it will be submerged. The new wall aims to provide unrestricted water and electricity supply.
Two free-standing Wolff 1250 B luffing jib tower cranes from Wolffkran, a Swiss-based tower crane manufacturer, will be used for the project over the next four years. A key job of the crane is to pour concrete from the 20-ton hopper into the formwork to build the new dam.
The crane will remain erected throughout the four-year period and will therefore be affected by the harsh alpine environment as the site is approximately 1,900 meters above sea level.
The cranes will stay in place because it is neither practical nor economical to disassemble, transport and store them every winter.
In order to withstand harsh mountain conditions, which can mean wind speeds of up to 220 km/h, avalanches and thick ice in winter, Wolffkran used 14 XXL TV 60 tower sections specially developed for this project.
The length of the XXL section is 6 meters, while the length of the standard TV 33 tower section is 3.3 meters.
Each tower crane uses 7 XXL segments with a height of 35 meters, providing a stable base for the free-standing tower crane. Then ten smaller TV 33 sections were used on one crane, resulting in a final tower height of 92.1 meters, and nine TV 33 sections were used on the other, resulting in a tower height of 87.1 meters. The taller crane has a jib length of 70 meters, and the lower crane has a jib length of 75 meters.
Crane parts are delivered on time
An eight-person Wolffkran team completed the installation in just two weeks. Due to site constraints, most crane components must be delivered "on time". This involved 70 trucks arriving at the site through winding mountain roads.
The constraints of the construction site also posed challenges for the installation team, who used 500-ton and 150-ton mobile cranes to pre-assemble the components on the ground.
In order to connect tower crane parts of different sizes, Wolffkran developed the VR 3360 connection frame. It has also developed and used TV 33 S-an enhanced version of TV 33, specifically designed to meet the high static requirements of the transition from the connection frame to the TV 33. Snow, wind.
Rolf Mathys, Managing Director of Wolffkran Schweiz, explained: “Ice surface, etc., known as rotating parts and ice flags on towers, must be taken into account as additional wind surfaces.” “In addition, snow and ice are actually heavy, so Has static relevance."
In order to provide the required stability for each crane, specially manufactured foundation anchors and more than 600 cubic meters of concrete are also used.
Wolffkran says this is about ten times the amount of concrete used for the foundation of a normal crane.
"Lapping on rock masses or dams is neither a technical nor economic option," Matisse added. "The stand-alone crane has a maximum lifting capacity of 20 tons in a single fall operation, and a maximum lifting capacity of 11 tons at a boom radius of 75 meters. It must be able to withstand wind speeds of up to 220 km/h, avalanches and icing. For The conventional Wolff tower system and standard calculations of the Wolff 1250 B are simply not feasible. Everything needs to be recalculated from scratch. At Grimsell, we are dealing with conditions that are completely different from standard construction sites."
The construction work will be carried out in double shifts in order to make full use of the short construction window before the return of winter. The crane operators for this job received extensive training from Wolffkran.
To keep the cranes moving, even if the mountain pass was closed due to snow, Wolffkran (in cooperation with a cable company) installed a cable system between the existing (old) dam and the crane.
In order to prevent the slewing parts of the crane from freezing, the slewing gear transmission and the motor are equipped with heating pads. The switch cabinet and engine room are also heated, and the slewing ring, winch and luffing rope are all coated with grease before the cold wave.
The automatic rotation procedure will be performed 2 to 3 times a day to loosen the icing-this process is poetically described by Mathys as a "crane ballet without spectators".
"This is a major effort, but it is still much more economical than disassembling and dismantling cranes every winter and reassembling them in the summer," Matisse concludes. "I believe our Wolffs will manage their alpine trip well. We are fully prepared for everything and are already in the planning stage of another alpine project."
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