External post-tensioning to support higher-productivity freight movements

Client: Far North District Council

Main contractor: United Civil Construction Ltd

Location: Broadwood, Far North

Contech scope: External post-tensioning and concrete repairs

System: BBR CONA CMS 106 anchorages

The challenge

Broadwood Road H16 Bridge needed additional structural capacity to meet changing transport demands. As part of Far North District Council’s programme to accommodate higher-productivity motor vehicles, strengthening the existing concrete bridge would help support freight movements and the communities that rely on the regional road network.

United Civil Construction engaged Contech to supply and install an external post-tensioning system, together with concrete repairs. Delivery required careful integration with the bridge’s existing geometry and reinforcement, and safe access beneath an operational structure.

Strengthening the existing structure

Contech installed steel deviator assemblies, anchorages and high-strength prestressing strands. The work involved threading, stressing and protecting more than one kilometre of strand. The external system applies additional post-tensioning forces to increase the capacity of the existing structure.

Reinforcement scanning and setting-out preceded drilling and anchorage installation. Working at height and over water required temporary access systems and controls for traffic interfaces, while stressing operations required specific procedures to manage the stored energy in the strands.

An anchorage developed for retrofit work

Contech proposed the BBR CONA CMS 106 anchorage system for the project, drawing on two years of development work with BBR in Switzerland. The system was designed specifically for external strengthening of existing concrete structures, where access and geometry can make installation difficult.

Each anchorage incorporates a concrete blister within a galvanised steel shell, with high-strength grout encapsulation. Dual fixing points using Grade 8.8 threaded rods provide fixing redundancy. The transition pipe arrangement accommodates up to five degrees of angular tolerance, giving the installation team flexibility when aligning the system with the existing bridge.

Durability was addressed through the hot-dip galvanised steel shell and grease injection to protect internal components after stressing. Together, these measures provide corrosion protection for the strengthening system.

Verification at each critical stage

A project-specific Inspection and Test Plan established hold and witness points from preparation through to completion. Checks covered reinforcement scanning, drilling verification, anchor installation, strand placement and corrosion protection.

Stressing calculations, equipment calibration and measured strand elongations were supported by documented inspection records. This provided verification of the installation and stressing process against the project’s requirements.

The outcome

The completed works increased the bridge’s structural capacity while retaining the existing concrete structure. Contech’s contribution combined specialist installation with an anchorage solution adapted to the practical demands of retrofit work: fixing redundancy, alignment flexibility and corrosion protection.

Broadwood demonstrates how external post-tensioning can help infrastructure owners adapt existing bridges to new transport demands, with specialist engineering applied to the details that determine how a strengthening system is installed and protected.