Abstract: A concrete structure in which a post-tensioned concrete slab is supported by columns, each column being surrounded or partly surrounded by an area of concrete in the form of a hollow inverted pyramid, the column passing through the apex of the pyramid. The area concerned is formed integrally with the remainder of the slab and is of substantially uniform thickness sloping downwardly from the surrounding concrete towards the column at an angle .theta. to the horizontal such that tan .theta. lies in the range of 0.1 to 0.25 or in the case of a column near an edge or corner of the structure 0.1 to 0.35.

Abstract: The invention relates to a structure, such as a cooling tower, comprising a waisted tubular envelope consisting of a membrane made of a material which is capable of supporting tension in all directions in its plane. The membrane is pre-tensioned and carried with its tubular axis upright from a support which provides the vertical component of the pre-tensioning.