Roof of Mairi Sewage Works Vienna

Walter Dürschmid

Subject | Timber is often used as a building material in environments where steel or concrete might be at risk due to the occurrence of aggressive vapours. This problem is frequently encountered in industrial situations. Here the emergence of laminated wood (glulam) has made the choice in favour of timber easier since this technology allows for large spans. Hence, timber is not only an extremely resistant material, but also suitable for large structures.

In Vienna the main sewage works are located relatively close to residential districts - which led to complaints from residents about strong, unpleasant odours. In 1987 the plant's operators decided to roof over the sewage facilities, to ventilate the ensuing enclosed spaces and treat the malodorous air in filters. The four sedimentation tanks, each with an outside diameter of 41.20 m, presented a particular challenge because for technical reasons, each tank had to be covered in one span. Laminated timber was chosen because of its ability to span such distances and because of its resistance to the extremely aggressive vapours given off by the sludge in conjunction with the very hot and humid atmosphere. The architect Walter Diirschmid was given the task of designing the roof and after considering a number of alternatives it was decided to opt for a single-span dome made from glulam ribs.

Location

Hauptkläranlage Wien, Haidequerstrasse 7, 1110 Vienna 11, Austria

Client

EbS - Entsorgungsbetriebe Simmering Ges.m.b.H., Vienna

Architect

Ing. Walter Dürschmid, Architect, Vienna Assistant Ing. Adamek

Structural Engineer Ingenieurkonsulent Dipl.-Ing. Peter Kramer, Vienna

Timber Construction Buchacher Holzleimbau GmbH, Hermagor

Date of Completion

Design and structure | The shallow dome with a rise of 6.85 m caused a considerable horizontal thrust at the supports which had to be resisted by an outside ring beam as ties across the base of the dome were of course unacceptable. The existing edge of the tank was inadequate, so a separately founded reinforced concrete ring beam was built around the outside of the tank. It is L-shaped in section and consists of 16 individual precast units supported by concrete columns. Anchored in the internal angle of the L-section are 20 mm steel bearing plates - exactly perpendicular to the incoming rib axis - as supports for the main ribs of the dome. Interesting is the fact that these support points are located at the joints between the precast concrete units making up the ring beam; this made the detail more complicated but meant that the concrete sections were not subjected to bending stresses due to the point loads.

Costs

The cost for all four domes, including all concrete works, was 48 million Schillings.

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