ABSTRACT

Circumferential prestressing of circular-cylindrical concrete tank walls is intended to eliminate the hoop tension due to hydrostatic pressure and maintain residual compressive hoop stress σϕr (–1.0 to –2.0 MPa or –150 to –300 psi) that is constant over the wall height. This ideal objective can be achieved only when the wall edges at the top and bottom can slide and rotate freely. With these edge conditions, the circumferential prestress that can achieve the ideal objective must produce trapezoidal inward pressure, normal to the wall surface. When the wall has constant thickness, this prestressing alone or combined with triangular hydrostatic pressure over the full height of wall produces zero moments M and Mϕ in vertical and circumferential directions. The only internal force is normal force Nϕ in the hoop direction. For this reason, tank walls are often provided with sliding, or partially sliding, support (elastomeric pads) at the bottom edge, while the top edge is left free. The advantage gained is avoiding or significantly reducing the bending moments, at the cost of material, installation, and quality control to produce a nonleaking sliding joint.