Construction of Cone Shaped Water Tanks using Post-Tensioning Systems
About 4.4 million people in the citystate of Singapore live on an area as small as 683 km2. Due to its geographical constraints and a population density of 6,400 inhabitants/km2, Singapore severely lacks sufficient natural drinking water sources. In the modern water processing techniques Singapore sees a possibility to solve its perennial water shortage problem.
The Public Utilities Board favors the term "recycling" for turning waste water into "ultra clean" water. This treated water called "newater" in Singapore will again have drinking water quality after elaborate treatment processes.
As a specialist subcontractor Utraco Structural Systems Pte. Ltd. (USS), DSI's licensee in Singapore, was significantly involved in the design and construction of two elevated cone shaped water tanks for the "Tampines Newater Service Reservoir" project. Construction of these elevated tanks was necessary to store recycled "newater" from a nearby water treatment plant. In particular, the storage capacities serve to supply nearby electronics chip manufacturing facilities with the ultra pure water they require.
The two elevated water tanks have a storage capacity of 8,448 m3 each and were 31.5 m above ground at their brims. The tanks have a maximum diameter of 43.0 m, a central access reinforced concrete core measuring 5.9 m in diameter and are capped at their top with a steel roof. The water tank walls were post-tensioned both radially and circumferentially using DYWIDAG Post-Tensioning Tendons. The tank walls measure 650 mm at their base, tapering to a lean 480 mm at their top. The internal wall surfaces were lined with HDPE in order to prevent contamination of the "newater" from its potential reaction with concrete.
The most challenging aspect of the water tank construction was the provision of a safe and fast in situ formwork and working platform system. Due to the planned height and degree of inclination of the tanks Utraco Structural Systems developed a modified jump form system that could handle fast concrete pours of up to 1.45 m in height. This modification allowed for the accommodation of the varying cast diameters after each pour and rendered the "fanning out" effect of the tank walls possible.
Thus the walls were successfully constructed using a total of 15 pours within the scheduled 7 days for each pour.