ANALYSIS AND DESIGN OF R.C.C. OVER HEAD RESERVOIRS

Abstract

Overhead reservoirs being important civil structures, their safe and economical design is essential. There are divergent opinions among the various research workers and investigators regarding the economical proportions of the container and the staging made up of columns and braces. Most of the investigators have investigated one part or the other of over head reservoirs. Therefore, the problem of optimal design of complete overhead reservoir i.e. design of container, staging and foundation is taken for study in this thesis. In an Intze type container the vertical cylindrical wall and the conical dome account for 70 to 80 Y. of the cost of the container. These have been replaced by segmental cylindrical shells polygon and conoidal conical shells polygon respectively. The economical proportions of the container have been worked out considering overall minimum cost of container apart from minimum weight. To achieve this objective, the proportions of various parameters of the container have been varied over a wide range. In all six capacities of the container ranging between 350 KL to 1500 KL have been investigated. The design is carried out by the working stress method and on no crack basis for the forces obtained from the membrane analysis. A framework of vertical circular columns connected by horizontal braces of rectangular cross.-section is selected for staging. The staging is analysed by the equivalent tube analogy for the horizontal forces. The staging is optimised by varying the number of columns and panels. The effect of the staging height is also investigated for the above capacities and four heights between 12 to 21 m for all the five seismic zones and wind zone II have been investigated. The foundation consists of a ring beam whose design is governed by the staging, and an annular raft. The annular raft foundation is designed for five bearing capacities of the soil ranging between 50 kN/m2 to 150 kN/m2. The foundation is also designed for wind or seismic forces. From the results economic combinations for foundation are recommended in the last Chapter. The cost of the various water tanks have been compared in terms of the equivalent volume of M20 concrete. Design charts are also prepared to design the overhead reservoir of any given capacity; staging height and bearing capacity of