Recently the growing community of Stansbury Park, UT, called upon its Improvement District to increase its water storage and live up to the expectation of providing quality water to its customers. In order to achieve that goal, the Improvement District hired Ward Engineering, a consulting engineering firm based in Salt Lake City, to design the project.
A circular tank was found to be the most efficient shape to contain the water. Prestressed concrete was chosen for the tank material. The goal was to provide a high quality, long lasting and low maintenance water storage structure. A prestressed concrete tank also gave the district the ability to bury the tank, reducing environmental impact.
Understanding the importance of a lifeline structure maintaining its integrity following an earthquake, the engineers incorporated a state-of-the-art seismic connection at the wall base and wall top to handle the potential high seismic forces that may occur in Tooele County.
This connection, typically referred to as a "free connection," allows each component of the tank (i.e. wall, wall footing and roof) to act independently of one another, which further enhances the ductile property inherent in concrete.
Gerber Construction, based in Lehi, UT, was awarded the general construction contract for the project, totaling $956,700, and completed the site work and tank floor, footing, wall, columns and roof concrete pours. The tank design consisted of a six inch thick membrane floor, perimeter ring foundation, a 10 inch vertically and circumferentially prestressed wall and round columns supporting a nine inch thick flat roof slab.
DYK Inc., El Cajon, CA, was awarded the tank prestressing contract, which consisted of vertically post-tensioning the tank wall with 84 high-strength threadbars and circumferentially prestressing the wall with over seven miles of galvanized seven-wire strand. The circumferential prestressing provided adequate force to resist the water load of the tank and account for the sloshing of the tank contents should the structure undergo an earthquake.
All stressing operations were performed with quality-controlled equipment that monitored and recorded the applied forces within a tolerance of 1.5 percent. The circumferential prestressing was then covered with several layers of shotcrete, an alkaline rich mix that will protect the strand from corrosion.
With an inside diameter of 105 feet, a 26.25-foot-tall wall and a column-supported flat roof, the new tank provides 1.6 million gallons of both fire and potable water storage for Stansbury Park, more than doubling previous storage.
