The 126 m tall Prime Tower's three concrete cores are being constructed with 51 of Doka's new SKE50

The 126 m tall Prime Tower's three concrete cores are being constructed with 51 of Doka's new SKE50 plus automatic climbers and 27 SKE50 plus shaft formwork units, all fitted with Doka timber-beam for

The latest addition to Zurich's skyline, the 126 m-high Prime Tower, is using Doka's new SKE50 plus formwork system and Xclimb 60 protection sheild to meet a strict construction timetable and saftey requirements. Richard High reports.

The international finance centre of Zurich has for years ranked among the world's top 10 most liveable cities. It also ranks highly as a prestigious business address, with many financial and insurance corporations systematically investing in property developments that promise potentially high yields.

Foremost among the latest generation of new developments is the Prime Tower, currently being constructed for Swiss Prime Site. At 126 m-high, the 36-storey tower will not only be the tallest building in Switzerland, but the undisputed landmark building of the new Zurich City West district.

Concreting work on the distinctive tower is using Doka's SKE 50 plus automatic formwork climbing system and its Xclimb 60 protection screen.

EPC contracting companies Losinger Construction and Karl Steiner are working in a consortium as lead contractor. Marti has been contracted to carry out the works on the structure shell with Doka's Swiss agents, Holzco-Doka, supplying 51 high-performing SKE50 plus automatic climbers and 27 SKE50 plus shaft formwork units, all fitted with timber-beam formwork.

The three cast-in-place (CIP) concrete cores are currently being raised in a weekly cycle to meeting the very tight completion deadline, which only allowed for 16 months for the shell.

"On this project, there are two factors that are absolutely critical for us, said construction supervisor Richard Mader, "fast cycle times in the in-situ concreting operations, and a high standard of safety throughout the shell construction phase."

The automatic climbing formwork and the protection screen were planned by the experts of the Doka Automatic Climbing Technology Competence Centre in Amstetten in close collaboration with the consortium's Site Management. Doka's involvement in the planning process from this early stage paved the way for fast, efficient forming operations.

Complex layout

The triple core of the Prime Tower presents challenges aplenty, including different layouts, pointed angles, narrow shaft dimensions and large wall thicknesses. Other requirements include the need to form the three cores separately to ensure maximum workplace safety, and fast cycles.

The totally remodelled SKE 50 plus unit is compact and boasts significantly longer lifting-travel than the SKE 50. It also comes with a new, integrated railing system, which, according to Doka, results in even shorter repositioning times and improved workplace safety.

Climbing the three cores independently has meant it's been possible to achieve a climbing cycle that is exactly matched to the progress of work, which boosts efficiency even further, said a Doka spokesman. What is more, he added, the climbing steps are timed so that all the outside platforms are moved up together, meaning that they are always located at the same level.

Shaft formwork efficiency

The new SKE50 plus also delivers efficiency gains when it comes to forming the inside walls of the shafts, added the spokesman. The SKE50 plus shaft system, another entirely new development, comes with a centrally positioned climbing profile that is fixed in the concrete by horizontal shaft beams with lever-latches, which rest in previously installed latch-box recesses.

Using the SKE50 plus shaft system means only one automatic climbing bracket is now needed in narrower cross-sections. This has given the consortium a substantial saving on equipment costs and improved productivity on the narrow cores. The wall formwork is fixed to Framax stripping corners I to make formwork boxes that can quickly be backed off the concrete in a few simple steps.

Swift progress

To ensure a "cost-saving work sequence", a 35 m-reach concrete placing boom is also being "jumped" from one casting section to the next in tandem with the formwork, by four SKE100 climbing brackets.

A major priority here has been to provide easy and safe access to this self-climbing "site within a site". A stair tower therefore extends from the top platform all the way through the self-climbing scaffold and down to the following floors. It is also moved upward hydraulically.

All the workplace access routes were planned to fit perfectly with the platform layout at a very early stage in the planning process. "This is a crucial factor for achieving fast cycle times on high-rise structures with repetitive working cycles", explained Doka project manager Manfred Wenger.

Protection screen

To safeguard the slab-forming operations, Marti decided to use the Xclimb 60 protection screen, which completely encloses the four top storey levels at any one time. Measuring around 2200 m², the protection screen is "climbed" up to the next level by easy-to-operate hydraulic cylinders.

The four split-level slabs, all with different widths, in storeys 9, 11, 18 and 27 are also no problem for the Xclimb 60, which is dealing smoothly with these areas using an ingenious adaptation method.

"To fix the protection screen to the building, we need two floor slabs directly above one another. When we have a floor-slab that cantilevers out further, we have simply used a steel construction to extend the floor-slabs below it out as far as the cantilevering slab. This enables us to safeguard all the storeys, without interruption", explained Holzco-Doka's technical manager and "formwork expert" August Morf.

There are also three loading platforms integrated into the protection screen. From these, the floor-slab formwork can easily and safely be picked up and lifted by crane.

Great support

The limited space available at this busy, dense location and the tight timetable, have necessitated both efficient site logistics and rapid construction progress. Meeting these requirements has seen Holzco-Doka ssupply many formwork elements with a high degree of pre-assembly, which has made a major contribution towards shortening the work preparation times.

By delivering to the site just-in-time (JIT), Holzco-Doka has also minimised the amount of onsite storage space needed, and considerably simplified the site logistics.

During the start-up phase, Doka foremen also instructed the site crew in how to erect and operate the automatic climbing formwork, which helped the forming operations on the CIP concrete core get off to a very quick start.

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