Christen Hill Reservoir

STI/SPFA 2016 Tank of the Year

Product / project title: Christen Hill Reservoir
Product / project owner: North Coast County Water District
Product / project location: Pacifica, CA
Date completed: October 2016
Construction standard (if any): AWWA D100, Sec. 14
Overall height / length (feet, inches): 67’ -0”
Column height (feet, inches): –
Diameter (feet, inches): 108’ – 0”
Capacity (US gallons): 3,750,000
Steel tonnage used (US tons): 365
Steel thickness (inches): 1/4” to 15/16”
PRODUCT / PROJECT DESCRIPTION AND SPECIAL FEATURES:
This project was a challenge to erect and paint due to its hilltop location in a high wind region, but the most significant aspect of this project is the specification implement by the water district to mitigate future corrosion problems in the tank roof.
Instead of utilizing minimum requirements of the AWWA D100 standard which results in inaccessible areas in the tank roof structure, the water district specified that all roof laps must be sealed and additionally that the supporting rafters must also be seal welded to the roof plates.
In lieu of conventional construction, the tank manufacturer designed a structure utilizing single-span, integral formed structural roof panels for the roof system.  This design reduced the required welding by approximately 50% thereby reducing the magnitude of weld shrinkage distortion to be accommodate by the erection methods.  With the fully seal welded roof system, the roof and integral structure were easily coated and will be easy to maintain for many decades into the future.  The strength and flexibility of steel are exemplified in this project by the ability to produce the single span roof panels at the minimum specified thickness of 1/4″.
By utilizing this approach of specifying above the minimum D100 requirements for the tank roof system, this tank has just begun its journey to membership in the highly respected STI/SPFA Century Club.

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