Late in 2013, BBR Contech were awarded the post-tensioning subcontract for the Westport Water Supply Upgrade, located on Waterworks Road, Sergents Hill, Westport. The subcontract package incorporated the supply of all post tensioning components, materials, equipment and personnel to complete the post tensioning and grouting.

The 34m internal diameter reservoir was constructed using 220mm thick precast concrete wall panels 4,730mm high with 11№ rings of 51mm ID plastic duct housing 7-strand post-tensioning tendons. Post tensioning was achieved using our 100 tonne hydraulic jack, pump, pressure gauge combination through 4№ pilasters (primary and secondary stressing) with half tank circumference duct (tendon) profile.

Post-tensioning requirements included the following:

• 44№ BBR Cona CMI 705 anchorages with anti-burst spirals
• 7.5 tonne of 12.7mm LR-SS (5-superstrand) tendons
• Stressing operations in accordance with Concrete Construction standard NZS 3109: 1997 section 8.
• Each tendon stressed to 80% UTS.

Each tendon was successfully tensioned with a resulting force slightly higher than initially calculated due to the reduced friction coefficient of the plastic duct.