A Common Mistake in Design of Water Tank

In this paper a common mistake in calculating the thickness the wall and corresponding area of reinforcement in the water tank by working stress method have been discussed. Due to water pressure, wall of the water tank is subjected to Tension and Bending Moment. In most of the books, the thickness of the wall and area of reinforcement for bending moment is calculated by following formulae considering cracked section t = + effective cover and Ast = When the moment of resistance of wall section (which is the least moment of resistance of wall considering as cracked and uncracked section) is calculated from the above values of t and Ast, it comes out less than the applied moment, hence design is not safe. Therefore, it is necessary to determine thickness and corresponding area of reinforcement of wall section in such a manner so that it remains safe in cracked as well as in uncracked condition. To overcome this problem, a simple procedure for calculating the thickness the wall and area of reinforcement in the water tank by working stress method have been discussed. In this paper, the thickness of wall is calculated considering it as an uncracked section ignoring area of reinforcement and area of reinforcement considering it as a cracked section. At the end, effect on area of reinforcement due reduction in thickness of wall of tank have been also discussed.