Towering expectations met without a hitch

This was not the first time the contracting company had worked in this Brussels neighborhood. It had already built the Dexia Tower, the Zenith Tower, the North Galaxy Tower in the immediate vicinity and the MG Tower in Ghent. With a height of 137 meters, facade skeleton included, the imposing office tower falls under the category of 'High Buildings'. This makes the Silver Tower the fourth tallest building in the country after the Zuidertoren, the Financiers Tower and the UP-site.

Bumpy preliminary process

The construction of the tower was not without controversy. The original building permit was delivered to construction promoter AG Real Estate back in 2010. Uncertainties surrounding the occupation of the building, an asbestos contamination on the site and doubts surrounding the awarding procedure threw a spanner in the works. The project was on hold for several years until AG decided to sell to Ghelamco. The latter quickly found a tenant (Brussels Capital Region) and was able to put the project on track. This allowed CIT Blaton to start construction work at the end of 2018. The construction time for erecting the shell was estimated at 18 months but was finally delayed by 5 weeks due to COVID-19.

Impressive figures

The Silver Tower, executed in an elliptical lens shape, was built on a rather narrow plot in Saint-Josse-Ten-Noode near the North Station and is enclosed between a major thoroughfare and the rail infrastructure of the North-South Junction. The footprint of the tower measures 28 m wide by 69 m long. The tower has 7 underground levels, a ground floor, 33 upper floors and 2 mezzanines. In total, as much as 16,000 m³ of concrete was largely poured on site and 2,000 tons of reinforcing steel was incorporated into the building, supplemented by precast columns, beams and vaults. The total surface area covers 45,000 m² and, once finished, will accommodate more than 2,000 civil servants of the Brussels Capital Region.

Time-saving construction method

Says Marjan D'Hose, project manager at CIT Blaton, "To save time, we applied the up-and-down construction technique (stross) here, a process we use more often on projects of this size. This stross technique allows us to work above and below ground simultaneously and avoids the prolonged presence of an inconvenient construction pit. First, the underground slurry walls were executed, which provide a "closed construction pit," and later the floor slabs were executed one by one. On the first slab (N-1), the above-ground construction could be started immediately. At the same time, work could continue on the underground floors: these were excavated level by level and the floor slab was always concreted on site. The excavated soil was removed through a small opening, without interfering with the construction work in the superstructure. Logistically, this was an immense challenge on this small construction site."

The superstructure of the tower consists of a central core, constructed by self-climbing formwork. "Around this were built column-beam-well structures that form the floors of the plateaus. A total of eight metal 'pulls' attached to the central core were provided from floor +16 to +18. They act as 'form-fixed' triangles, to create such a slender and tall building. The tractors are equipped with hydraulic dampers that will ensure that the settlement differences between the core and the facade are absorbed (slow deformations), but do not allow a deformation due to sudden, large forces such as wind, for example. This technical feat was devised by the engineering firm Greisch and acts as a 'smart elastic' alternative to a form-fitting triangle, thanks to the use of hydraulic dampers in the tractors."

CIT Blaton is a family company with independent shareholding and has grown to become one of the country's leading construction companies over a span of 155 years. In doing so, it couples traditional techniques with advanced technologies, with a strong focus on sustainability. With the realization of the Silver Tower, they also easily met the sky-high expectations of all parties involved.