Tanks

Reinforced concrete tanks have been used for water and wastewater storage and treatment for decades. Structural engineers are asked to design a variety of square, round, and oval reinforced concrete structures that may be above, below, or partially below ground. Design of reinforced concrete tanks requires attention not only to strength requirements, but also to crack control and durability. The challenge for the structural engineer is to design concrete liquid containing structures that will resist the extremes of seasonal temperature changes and a variety of loading conditions, and remain watertight.

Code Requirements

ACI 350-06 Code Requirements for Environmental Engineering Concrete Structures extends the basic ACI 318 Building Code Requirements for Structural Concrete with additional serviceability requirements for crack width control due to flexure, shrinkage of concrete, and temperature movement. The commentary of ACI 350 makes it clear that ACI 318 requirements alone will not produce watertight structures. ACI 350 serviceability requirements include:

• Reduced working load stresses, and requirements for size and spacing of reinforcement

• Increased minimum reinforcement for temperature and shrinkage movement, which is dependent on the grade of reinforcing steel and the length between shrinkage dissipating joints

• Waterstop requirements at all joints

• Concrete mix design requirements

• Increased cover requirements compared to ACI 318

• Commentary suggestions for use of shrinkage compensating concrete per ACI 223