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Rectangular tanks with rounded corners are a "best of both worlds" solution to the age old question of round vs. square tanks. Round is the ideal structural shape, the most economical shape to contain a given volume of water. Square uses the available site area most efficiently. Rounding the corners of these otherwise square tanks eliminates the highest wall stresses, in the corners, while allowing the site area to be used with minimal waste.
The rounded corners of these tanks allow the walls to be post-tensioned horizontally, using the same type of tendons used in our circular prestressed concrete water tank designs. Several other special features were designed into these clearwells to virtually eliminate cracking. A compressive force is applied to the monolithicly placed floor and roof slabs as soon as possible after the concrete placement by very early partial stressing of their post-tensioning tendons. Once the partial prestressing is applied, it is impossible for shrinkage cracks to develop. A special wall-roof joint detail allows the newly placed roof concrete to shrink without longitudinal restraint while still providing for the necessary transverse support at the tops of the walls.
(Note that these rectangular tanks have rounded corners.)
The rounded corners of these tanks allow the walls to be post-tensioned horizontally, using the same type of tendons used in our circular prestressed concrete water tank designs. Several other special features were designed into these clearwells to virtually eliminate cracking. A compressive force is applied to the monolithicly placed floor and roof slabs as soon as possible after the concrete placement by very early partial stressing of their post-tensioning tendons. Once the partial prestressing is applied, it is impossible for shrinkage cracks to develop. A special wall-roof joint detail allows the newly placed roof concrete to shrink without longitudinal restraint while still providing for the necessary transverse support at the tops of the walls.
(Note that these rectangular tanks have rounded corners.)
As part of an expansion and upgrade to the Indianapolis Water Company’s existing water treatment facility, we designed this 7.0 MG fully buried water storage tank to aid in treatment upgrades and provide additional storage to meet government regulations. This design-build tank included a rectangular post-tensioned concrete clearwell with rounded corners. It also has horizontally and vertically post-tensioned walls, and a post-tensioned two-way flat plate mat foundation designed for four feet of water uplift. This relatively large tank has a monolithically placed post-tensioned, two-way flat plate floor and roof in order to prevent cracking and possible water contamination. It is fully buried, with two feet of backfill over the roof. The corners are rounded to a 40-foot inside radius, a feature that also helps avoid wall and roof cracking.
