Circular prestressed concrete tanks: a new approach to the analysis

Abstract

The behaviour of a circular prestressed concerte tank is closely dependent on its wall-to-base connection, which can be either monolitic or hinged. When the capacity of the tank is small or medium, a monolithic connection is widely accepted, due to construction, stability, watertightness and maintenance reasons. However, teh important fixed-end foces can jeopardize it's use on higher capacities. Within the different methods to analyse circular tanks with monolitic base-to-wall connection, it is usual to study the wall apart from the floor slab, assumuing the lower edge of the wall totally fixed. The course of the horizontal prestressing is equal to the course of the hydrostatic pressure. The solution of the problem is easily given by tables or by analitical expressions. However, some studies with analitical models that consider the soil-tank interaction show that the fixed-end forces are very sensitive to a small rotation of the connection. This paper presents a new approach to the analysis of the main forces of a circular prestressed concrete wall, with free edge at the top and monolitica wall-to-base connection, by comparison with the forces calculated assuming the base totally fixed, taking into account the movement capaciry of the connection (defined by the thickness of both the wall and the base slab and by the soil mechanical behaviour). The proposed method is based on an analitical linear elastic model that considers the soil-tank interaction under axisymetric loads. The important difference between the forces calculated with this method and those calculated assuming the lower edge of the wall totally fixed results in a considerable saving in materials and in a largest range of use of the monolithic connection.