Design, Inspection, and Analysis of Wire-Wrapped Concrete Water Tanks, Prestressed Concrete Water Tanks, Post-Tensioned Concrete Tanks Design, Inspection, and Analysis of Wire-Wrapped Concrete Water Tanks, Prestressed Concrete Water Tanks, Post-Tensioned Concrete Tanks
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Design, Inspection, and Analysis of Wire-Wrapped Concrete Water Tanks, Prestressed Concrete Water Tanks, Post-Tensioned Concrete Tanks
Design, Inspection, and Analysis of Wire-Wrapped Concrete Water Tanks, Prestressed Concrete Water Tanks, Post-Tensioned Concrete Tanks


Terminal Island ESDs

Steven R. Close, when he was working with VSL Corporation in the late 1970s, helped design the post-tensioning tendons for the Egg-Shaped Digesters at the Terminal Island Wastewater Treatment plant, in Los Angeles, CA.


The horizontal tendons are the in-line Z 5-6, known as the “Z” anchorage system. Each circumferential tendon has 4, 6 or 12 - 0.5 inch diameter strands that anchor, each way, into large steel “blocks.” The “dead” ends anchor at the tops and bottoms of the anchorages, while the “live” ends pass through the centers of the anchorages, pass through a “banana nose” into the stressing ram. As the tendon was stressed, the anchorages moved within elongated horizontal “blockouts” (shown as dark areas in the photo) every 120 degrees.

The vertical tendons were L (for Loop) tendons. The bottom anchorage was a smooth steel tube with the inside edge flattened, in a “D” shape. The top anchorages were ordinary multi-strand anchorages. The vertical tendons were stressed at three horizontal construction joints and at the top of the egg. The number of strands in each vertical tendon varied with the height, and wall thickness, of the egg.


Jorgensen and Close Associates (J&CA) designed the concrete foundations and the gallery building for the four steel ESDs at the Theresa St. WWTP, in Lincoln, NE. J&CA were the structural sub-consultants to Brown and Caldwell for this portion of the work.

The ESDs were supported on piles with conventionally reinforced pile caps. The gallery building and access tower were also conventionally reinforced concrete.