Futuristic mega project in Frankfurt: FOUR

In the heart of the city of Frankfurt, the visionary skyscraper project “FOUR” is rising higher and higher with each passing day. This is being made possible by Liebherr’s state-of-the-art luffing jib cranes, including the world's first to feature pioneering fibre rope technology. Liebherr and its partner Nagel Baumaschinen are working hand in hand with project developer Groß & Partner to bring the vision to life.

Situated along the Main River, Frankfurt’s impressive high-rise panorama has led to the city being dubbed as “Mainhatten”. The skyline is already dominated by an array of skyscrapers and now four more towers, ranging from 100 to 233 metres in height, are set to join them. “FOUR” impresses with its future-oriented architecture and sustainable urban development concept. The site in question is located in the banking district, right next to the Commerzbank Tower; the tallest skyscraper in the European Union.

But the project is about much more than just building more high-rises. “Our approach is what I like to call clockwise planning. We ask ourselves how people live their day: when do they get up, what routes do they take, what infrastructure do they use, where do they spend their time? This helps us determine which spaces we need to create so that people feel comfortable in the FOUR,” says architect Ben van Berkel.

He and his team from UNStudio were faced with the challenge of reconnecting and revitalising an area that had been cut off from urban life for decades. Led by the maxim “Live the city”, they aim to achieve this with a concept that offers something for everyone: offices, apartments, restaurants, cafés, hotels, public spaces and new connections to the city centre will be created on the site. “FOUR” thus breaks with single-use thinking and caters for a variety of purposes.

Variety is also an apt choice of word to describe the Liebherr tower cranes being used. At peak times, up to nine luffing jib cranes of different sizes can be working simultaneously on the towers: two 357 HC-Ls, two 280 HC-Ls, four 230 HC-Ls and one 258 HC-L Fibre. Having so many HC-L cranes on one construction site is something quite unusual, especially in Germany. With maximum lifting capacities of 16, 18 or 24 tonnes, they are ideal when it comes to transporting various building materials such as steel, prefabricated parts, and glass. In addition, an 85 EC-B flat-top crane on one of the high-rise roofs is helping with smaller lifting and façade work in the completion of the smallest building tower.

Nagel Baumaschinen and Liebherr assembled the first crane back in January 2021. The last crane is expected to finish its work on site in spring 2024. High lifting capacities, high-quality in-house manufactured drives, and impressive hook heights – all this and more supports the customer with efficient construction site operations. HC-L cranes are a particularly good fit in a large city like Frankfurt, which has a wealth of projecting edges due to its tall buildings. Thanks to their tight working radii and flexible jibs, they make optimal use of the limited space available. Nagel Baumaschinen and the Liebherr Tower Crane Center have both invested in this state-of-the-art equipment: four HC-L cranes belong to Nagel Baumaschinen, five to the Liebherr Tower Crane Center.

The use of a 258 HC-L 10/18 Fibre marks a world first. “FOUR” is the first construction site ever to have a Liebherr luffing jib crane with fibre rope. Fibre cranes achieve significantly higher performance values compared to their steel rope counterparts. In general, HC-L cranes specialise in high hook heights, and the advantages of the lighter rope are particularly evident at such heights.

Fibre rope is more durable, easier to handle when reeving due to its lighter weight, and maintenance is less complicated as lubrication isn’t required. And on top of all that, operational safety is also increased; crane operators are able to see at a glance when the fibre rope needs replacing due to wear or damage. The components of the rope’s cover wear out at different rates – when the red coated core becomes visible, it’s a sign that the rope has reached the end of its service life.

Liebherr began supporting project developer Groß & Partner long before the first crane was erected. Liebherr’s project department Tower Crane Solutions specialises in providing advisory services and planning crane operations for projects like “FOUR”. Holistic concepts, developed by experts in close consultation with sales partners and customers, ensure economical crane deployment planning. Tower Crane Solutions maintains a constant dialogue with all parties involved until the crane assignment is completed, in order to factor in crane positions, climbing stages and possible changes to workflows on site as early as possible.

“I’ve been involved throughout the project to varying degrees since 2017," says the Liebherr project manager in charge, Julia Scherzinger. “FOUR is my baby.” She regularly takes a look at the webcams or visits the construction site to observe the progress and, if necessary, coordinate any technically necessary adjustments in the construction schedule with the responsible planners from Groß & Partner. “Everyone who gets to be part of this project is passionate about it. Working with Groß & Partner is on equal terms, fair and transparent,” says the Liebherr project manager. “Just like a family, we put our heads together when challenges arise and collectively come up with a solution.” This close and deep cooperation is a central factor for the success of the entire large-scale project.

Hardly a month goes by without at least two cranes increasing their hook height further. The tallest crane is working at a tower height of 243 metres, the lowest climbed crane at 132 metres. The luffing jib cranes climb on the inside and outside of buildings. This concept, which has also been developed by Tower Crane Solutions, has a number of advantages. The outside-climbing cranes can dismantle the inside-climbing cranes at the end. So no additional lifting equipment is required. The cranes climbing externally on the building climb down independently to a minimum structure height and can then be finally dismantled cost-efficiently with a mobile crane.

The concept also requires fewer tower sections than if all cranes were to climb on the outside. This saves costs and CO2 emissions that would have resulted from the delivery of additionally needed tower sections. Experienced service technicians from Nagel Baumaschinen and Liebherr carry out the climbing stages to ensure a safe process and as little downtime as possible for the crane concerned. As of the end of April, 40 climbing stages have already been successfully completed.

Senior site manager Roger Schmitt from GP Con GmbH, a subsidiary of Groß & Partner, says, “Our collaboration with Liebherr has been characterised by great motivation, technical expertise and teamwork ever since we started construction work on the FOUR. (…) With nine cranes on a relatively small, inner-city construction site, coordination, simultaneous operation, and the sometimes weekly new climbing phases of these cranes have been, and continue to be, a huge challenge. It can only be done with exceptional preparation, joint planning, and punctual implementation. With Liebherr and Nagel Baumaschinen, we have reliable and competent partners at our side who contribute to the positive progression of this project through their own initiative and good ideas.”

Project Website Groß & Partner

The four new towers in Frankfurt are expected to be ready for occupancy by mid-2024, with the exception of a few smaller elements. By then, the Liebherr cranes will have transported a fair amount of material from A to B over a period of approx. 1,275 days:

- 60,000 tonnes of reinforcing steel

- 1,500 tonnes of steel girders and construction components

- 4,000 semi-prefabricated ceiling panels

- 2,000 semi-prefabricated beams

- 750 flights of stairs

- 1,152 prefabricated pillars for Tower 1 and 4