World Trade Center IV in Brussels

Construction of a 26-storey fourth office tower (± 100 m high) of ± 35,000 m² floor area on an existing structure constructed at the beginning of the 1980s.

The main structural constraints are dictated by the shape and the strength of the existing structure and, in particular, the position of the core and of the columns.

The structural design has been guided mainly by these constraints. The basic option consists of demolishing to a minimum the existing structures in order to gain as much advantage as possible of the existing elements and, especially, of the foundations, but retaining the objective of not being restricted by the existing building.

The suspended floors therefore need to be designed using very high-performance techniques in terms of weight. The suspended floors have a mixed steel/concrete structure, in order to combine the best qualities of these two materials.

The ground area occupied by the new tower is greater than that of the original tower. Parts of the foundations (those on grid line 36) are indeed insufficient to take the new loads. Therefore, the use of complex structures allows the excess loads to be transferred to foundations that can support them. These structures are steel and triangulated. They are located on the roof in mainly technical areas, in order not to penalise the flexibility of fitting out of the lower floor levels. This kind of structure requires cutting-edge design and construction techniques that take into consideration both problems of deformation and strength and of erection.

The additional floor levels added to the smaller building on the site have been designed so as not to need the strengthening of the existing upper floor levels. Strengthening walls will only be required at level -2 on the raft, to be compatible with its strength.

All the new horizontal forces (tower and smallerbuilding) are taken by the new core, especially designed to contain the various technical, architectural and structural functions. Cutting-edge design using complex structural design software, allow the sections of concrete and of reinforcement to be optimised.