Analyses and Design of Elevated Water Tank Components

The builders of an elevated water tank sought CTLGroup's help with its structural analysis and design. The elevated tank's composite design consists of a 2-million-gallon steel water tank, supported on a reinforced concrete dome and ring beam, which is elevated approximately 100 ft above grade on a cylindrical reinforced concrete tower.

CTLGroup's scope of work included:

  • Evaluation of alternate teel-tank-to-concrete-ring-beam connection configurations.
  • Structural analyses of the steel tank, concrete ring beam, dome and support tower.
  • Design of the steel-to-concrete connection plate and anchorage, design of reinforcement for the ring beam, dome and upper portion of tower concrete, and
  • Furnishing design drawings.

CTLGroup performed structural analyses that included axisymmetric finite element analyses of the lower portion of the steel tank and upper portion of the concrete pedestal (dome, ring beam, and upper wall) for loads due to dead load of the structure, water pressure, and differential shrinkage, temperature, and creep effects. The connection evaluation used a detailed model of the steel-to-concrete interface region and a complete triaxial stress-strain model (Amad and Shah) to account for increased concrete strength under a triaxial stress state. Temperature loading conditions included thermal analyses for rapid increases and decrease in ambient temperatures based on climate records and the resulting stress effects on an empty steel tank connected to a relatively massive concrete ring beam. Reinforced concrete design included buckling analyses for the dome and crack control reinforcement in areas of potential high tensile stresses.