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Rabobank’s executive centre building has been renovated in a highly sustainable way. The new design consists of two 105 meter heigh towers, placed at a slightly different angle, connected with a skin of glass.
Originally the Rabobank’s executive centre building consisted of two practically independent towers that were to be connected by just a few walkways. From a structural point of view this did not appear very efficient. A great deal of space would then be lost to the additional necessary stabilizing elements. Constructively it was better to couple both towers across their full height. The two concrete cores could then provide the required stability. This basic principle was adopted by architect Rob Ligtvoet van Kraaijvanger in order to increase the plasticity of the towers.
The so-called Plaza with all kinds of public functions and meeting facilities is located below the towers. It was to become a monumental space in which the use of columns seemed unavoidable. The forces from the tower had to be transferred to the foundation. ABT conceived of a structure that keeps the Plaza free from columns.
This of course had a potential impact on the thickness of the Plaza’s ceiling roof. After all, it had to reroute the forces. However, the architect wanted this floor to be of the same thickness as the other floors in the tower, which due to the exceptional glass construction retained their visibility. This is why it was decided to install a truss floor, so that the floor could remain 28 cm thick. By incorporating a lowered ceiling into the design, the truss structure has been eliminated from view.
These structural interventions in particular further enriched the architecture.
The idea of giving the building a different type of foundation has significantly reduced construction costs. A fairly strong load-bearing sand layer is situated under Utrecht that is sufficiently strong for constructing low-rise buildings on natural foundation. A ‘standard’ pile foundation is used for high-rise construction, however. ABT investigated the feasibility of founding the 105-metre tall towers on natural foundation as well. However, the subsidence proved to be significant: ten centimetres. This is why a pile plate foundation was conceived. A key part of the building rests on natural foundation. Piles were driven in areas where the forces would be too great. This means that only half of the normally required number of foundation piles is now required. By combining these two foundation principles, subsidence was limited to only two centimetres the same degree of subsidence as would have been the case when a standard pile foundation had been used.
The car park was also optimised during the design process. The initial plan included a car park spread over two floors beneath the entire complex. A study conducted by ABT clearly indicated that it would be cheaper to construct the garage deeper – it now has four floors – as a result of which it is of course much smaller in size. This made it possible to construct the garage adjacent to instead of below the towers. As a result, the construction of the towers was separated from the parking garage. This resulted in significant time savings.
Team Rabobank Head Office