The North-East Kirchberg water tower will be located at the edge of the Grünewald forest and at the focus of the curve of the Boulevard Pierre Frieden. As such, it will form a visual landmark built in dialogue with the nature that surrounds it.
It should also, and this is its unique character, constitute a reception area for wildlife. In our conception of the project, we wanted to take this last requirement as a basis for reflection rather than integrating it a posteriori. In other words, it is not a question for us of building a castle on which to implant various nests, but of achieving a construction that shelters the fauna and forms a structure capable of integrating the elements that make up a water tower. Just as when we work on a collective housing building, it is the different types of apartments for the different types of users that are initially the focus of our attention. Then, once these elements have been mastered, they are combined and declined to form a coherent architectural whole.
For the water tower, we have studied the way of making the different models of nests according to the particular criteria of the desired species, then we have developed them so that they form the blocks of a building set that can form a collective building, a hotel for these different species. This is the rear of a treated area where there is no nest.
The form we have reached with this simple and economical constructive system stems from the static constraints of the reservoir and wind load recovery, but also from the desire to present a different profile in all directions, in order to provide a real point of reference for observers.
As many birds form light, dancing clouds, this construction method, made up of hundreds of similar elements, and its no less peculiar shaping give the building lightness and elegance. The cut-out in the sky that evokes flight is extremely important from this point of view.
The blocks are arranged in an ellipse at the base at level 0.00 and in such a way as to follow as closely as possible the two tanks at the altitude of +31m. It evolves from one shape to the other between these two levels and then widens afterwards. The number of blocks on a continuous level is constant, the perimeter increases as one goes up and the blocks are more and more spaced. From the top of the reservoirs, the number of blocks gradually decreases until the +50.00 level, which gradually clears a platform for observing the entire Kirchberg Plateau and, far to the west, the City.
The ground projection of the whole is 298m2 but each level has a much smaller footprint. The surface area at the base is 150 m2 for example.
A significant proportion of the blocks are arranged as nests and receive untreated wood siding. This facing is ventilated and arranged in such a way as to best fulfil its function as a shelter for different species, particularly bats.
The sided blocks are distributed in a seemingly random pattern to emphasize the cloud effect. However, the modification meets the following proportions: 0% for the first 4 metres, 30% from 4 to 20 metres and 70% thereafter, and respects the layout of the nest types according to the compatibility, orientations and altitudes of each species.
The nests for swifts and bats are integrated into the blocks with wood facing via a reservation in the central part of the concrete block and integrated into the formwork.
The nest for the peregrine falcon is integrated in one of the spaces between the blocks. The orientation and the altitude allow a possible access via the access landing to the tanks.
These arrangements can be adapted until the end of the project's development according to the requirements of wildlife specialists. The project is flexible in this respect. We also believe that the interior volume accessible at altitude through the interstices between blocks may create a good potential for species, to be examined with the specialists.
Presentation of the structural party and the technical party
The supporting system and the castle facade are made of blocks measuring 200cm long x 50cm high and 40cm deep.
From a structural point of view, the contact surfaces between the blocks are continuous and in alignment with each other so that continuous lines of compressive stress are obtained, forming vertical "pillars". Even under wind loads, the calculations made at this stage show that the uplift forces are few and only present in the upper parts where few gravity loads are applied.
In order to ensure sufficient strength and to avoid disorder in the event of accidental loading, a connecting reinforcement is provided between the blocks. For this purpose, the blocks have an oversized vertical recess at each end providing an appropriate positioning tolerance. During assembly, the blocks are wedged in place and then cemented in mortar without shrinkage. The reinforcements will pass through the recesses in the blocks, which will then be filled with a non-shrink concrete grout.
The blocks will be numbered and a tracing in the workshop will allow to materialize the contours of the support line of the upper blocks. This is to assist in the erection process and avoid the need to systematically survey each stratum during erection. However, surveys will be carried out every three or four beds in order to check the general geometry of the structure, but they will not be necessary for the positioning of each block.
The upper face of the blocks incorporates a slope to avoid water stagnation.
In the lower part of the tower, for the first 4 meters, the space between the blocks will be closed by a filling to ensure that any catch that could invite potential climbers is eradicated.
The advantages of working with prefabricated blocks of this type are :
-System repetitive and simple as some children's games,
-Low cost and simple and controlled technology as it is linked to the cost and the realization of simple geometric elements in reinforced concrete.
-Perennial and good patina in time
-Pre-fabrication allows off-site work to be prepared off-site, which allows upstream work to be carried out under good quality conditions in the workshop and with limited waste. It also allows a quality and aspect control before implementation.
-Allows to avoid complex formwork in height.