Design criteria of the circumferencial prestress of circular concrete tanks with monolithic wall-to-base connection

Abstract

The main aim of the circumferential prestressing of the wall of a circular cylindrical concrete tank is to counterbalance the hoop tension due to liquid pressure, but also to counteract secondary hoop tensions due to other causes such as temperature, shrinkage and assymetrical loading. For a wall with a monolitic wall-to-base connection, the displacement at the bottom edge is restrained, and the prestressing near the base does not produce hoop compressive forces. In fact, it produces high vertical bending forces. In order to reduce those fixed-end forces, many authors have propossed several imporved prestress distributions that redistribute the curcumferential prestressing in the lower part of the wall, placing the tendons where they are most effective in producing hoop compression. This paper presents a comparative study among five prestressing funcionts, proposed wither by the authors or in previous research works. The study is carried out with an analitical linear elastic model that considers soil-tank, and based on several basic design requirements previously defined. An optimization procedure for determination of the horizontal tank prestress is suggested, thus defining both the shape of the function and the minimum prestress force needed to ensure fully compressive membrane forces under the hydrostatic load. Furthermore, some significant differences are pointed out between some of the results in this study and those presented by other authors in the literature, basicly due to the fact of taking into account the real movement capacity of the monolithic wall-to-base connection in the analysis model.