Monitoring NZ's road bridges and ports

By Richard Curtis, Business Development Manager, WSP Opus Research

Since 2014, Opus Research has been developing a remote infrastructure monitoring system for the purpose of monitoring the structural integrity of assets anywhere. Initially, we were interested in aging, reinforced-concrete bridges that were past their design lifespans and were carrying traffic volumes and loads far in excess of what they were originally designed for. Monitoring would provide actual data on how a bridge responded to dynamic loading from maximum-weight trucks that could be fed into Finite Element Models which the engineers use in decision-making about bridge structural performance.

Opus Research needed to overcome a number of hurdles in developing the monitoring system. In particular it needed to:

• Be low-cost, as we envisaged it would eventually be used on numerous bridges where asset owners have limited maintenance budgets;
• Have minimal power consumption, as most bridges don’t have mains power, so it would run on batteries and solar recharge;
• Be able to transmit data wirelessly from remote locations, with dataloggers able to be remotely configured; and
• Capture, process and transmit data in real-time, including data from a range of different sensors with vastly different data capture rates, anywhere between 200Hz and once every hour or longer.

Opus Research developed the system over several years, focusing on miniaturisation as part of the quest for low cost and power, bringing the datalogger and battery management system down from something that was originally the size of a small suitcase to that of a shoebox, and a tenth the price.

Since 2014, Opus Research has been monitoring the Rakaia and Rangitata River bridges that are now carrying High Productivity Motor Vehicles (HPMVs) – over 55 tonnes. Providing structural response data for the first time was illuminating for the engineers who discovered the bridges weren’t behaving in the way they had expected them to. The Rakaia River Bridge, with 144 spans, was responding to heavy traffic in groups of five spans at a time, and, as a result, Opus engineers revised the theoretical models they had been using to reflect reality. It has demonstrated that the bridges have load capacity for HPMVs, saving the Agency over $10m in unnecessary upgrade costs.

Opus Research is now monitoring 12 bridges around New Zealand, seven of which were severely damaged by the November 2016 earthquake. Providing real-time data to the engineer’s dashboard for four Blenheim bridges meant they were able to carry vehicles, keeping the South Island road links open. The sensors provided decision-making data around vehicle speeds, numbers of lanes that could be open on each bridge, and whether movement in bridge decks was temporary or trending.

We also monitored the CentrePort wharf in Wellington as it was being rebuilt post-earthquake. Contractors were worried about two large container cranes on the wharf. An array of 10 tilt meters, linked to an alarm, alerted contractors to any sudden or trending movements. This saw the wharf evacuated several times and led to revised sequencing of new pile driving to stop the wharf tilting. It was a substantial success for worker health and safety and efficiency of the wharf rebuild.