The basis for the success of prestressed tanks is in two areas. The first is the steel shell diaphragm that is the heart of the wall and which makes the wall impermeable. The second is the bonded prestress wire which is applied under full load giving a uniform, measurable prestress force around the full circumference of the tank. Shotcrete, fully encasing the prestress wire, bonds it to the wall and prevents corrosion.Sectional information
The tanks can be divided into the following sections. Click each section for pictures and a description of that part of the tank.
Our standard floor is a 4" thick reinforced concrete slab designed to act as a flexible membrane slab in accord with AWWA D-110. The floor is vibratory screeded to consolidate concrete and obtain encasement of floor reinforcing steel. After applying a light broom finish the floor is water-cured until tank construction is complete. A highly reinforced 4" membrane slab is able to withstand a maximum differential settlement between the center of the tank and the wall as determined by y= 3 * 10-3 * r2/t (where y = settlement, r= tank radius, and t=floor thickness). Where site conditions generate a differential settlement greater than that allowed by the above equation, a structural floor should be considered. We design and build structural floors for many applications including piles, vibral compaction, rock anchors, tension piles (due to high water table), and ballast slabs (also due to water table).
After shooting the wall we construct a false work of shoring, ribs and plywood decking and pour a reinforced concrete roof in a thin shell spherical shape with a rise of one tenth of the tank diameter. The dome will be a free span, self supporting system with no interior columns of supports after the prestressing process is complete.
Prestressing is the process of wrapping the tank wall with a continuous steel strand under high tension to keep the tank walls in constant compression even when the tank is filled with water. The placement of the prestressing wire forms a continuous uniform helix of such pitch as to achieve the unit compressive stress required to maintain residual compression of the core wall when the tank is full of water. Extra prestressing in the dome band serves to counteract the radial thrust of the dome weight pushing the top of the wall outward, thus the dome is free standing with no interior supports.
Special exterior finishes may include architectural finishes, special painting formats or unpainted tanks.