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Undergraduate Project Report - Design of Rainwater Storage Tanks for use in Developing Countries

S. J. Turner (2000)

This project is to investigate the problems associated with ferrocemnet water storage tanks in developing countries, with the aim of giving the engineer a series of practical tips that will help with tank construction in the field. Using the findings of the project a series of a construction rules have been produced. The aim is to overcome the problems that are particular to constructing ferrocement water tanks in hot dry climates.

In rural areas of many developing countries, there is a scarcity of water. Traditionally, rainwater collection has provided valuable source household water. Therefore there is a need to provide simple, economical storage facilities that can be constructed with semi or unskilled labour. Approximately 80% of the cost of a ferrocement tank is the construction material. Due to the high cost the majority of water tanks are financed through donor funding. To enable self-sufficient production material costs need to be reduced. This project looks at efficient ways of reducing material inputs.

The first stage is to carry out structural analysis. For this thin shell theory has been used. Excel spreadsheets have been produced to allow the designer to vary the range of tank configurations and material characteristics. Initial findings from the analysis show that cylindrical tanks with curved walls can withstand greater loads than cylindrical tanks with vertical walls. Comparing a Thai jar (figure 2.7(b)) style water tank to standard cylindrical tank (figure 2.7(a)) of a similar volume material inputs can be reduced by approximately 30% (assuming the material is homogeneous).

Little is known about the mechanics of shrinkage, therefore this has been the focus of the experimental work carried out on ferrocement tanks. The author’s new physical test shows how shrinkage can be reduced through the use of reinforcing. A range of reinforcing systems has been tested and results show that a thin-wire steel square mesh is the most effective of the three examined.

The report investigates how the environment in which the tank is constructed plays an important role in the degree of shrinkage and cracking. It is shown that tanks constructed in a hot and dry environment and tanks that are allowed to set at different rates are much more susceptible to cracking.

 

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