by Dr Maria Rashidi, Lecturer, Centre for Infrastructure Engineering at the School of Computer, Engineering and Mathematics (SCEM)

There are now over 900,000km of roads and over 50,000 bridges in Australia, with millions of commuters relying on the transportation network. The reliability and safety of these infrastructure elements are crucial to the Australian economy, especially when it comes to the structural health of the country’s bridges.

Bridge inspection is an essential element of any Bridge Management System (BMS) particularly for aged and deteriorated bridges and a pathway to condition rating. The accuracy of condition assessment is relied heavily on the quality of inspection.

The ever-changing dynamics of infrastructure asset management and the success of accommodating to these changes is mainly in credit of adopting different technologies and methods of construction, inspection and maintenance. Remotely Piloted Aircrafts (RPAs), commonly known as drones, have been heralded as one of the next big developments in technology. However, until recently, very limited research has been done to investigate the benefits of the technology for use in bridge inspections.

The use of drones is one such technology, favoured for their features of safety, functionality and sustainability in the processes of infrastructure inspection. Building this bank of proof is necessary for government organisations and transportation agencies looking to move bridge inspection into the 21st century.

Figure 1. Drone Inspection of Peats Ferry Bridge

Figure 1. Drone Inspection of Peats Ferry Bridge

Tech features that need to be considered

RPAs have become an increasingly familiar technology and have become smaller, more capable and less expensive because of both military investment in the RPA industry and improved technology. Current generation of RPAs can be transported in small vehicles and launched from a road or a small truck but are still large enough to be equipped with cameras and sensors that can provide low-cost aerial information. These aircraft are capable of flying autonomously and completing pre-set flight paths.

Bridge inspection drones need to have advanced safety features considering that they fly over traffic, are subject to gusts of wind and weak GPS signals. Furthermore, the drone needs to be quite robust in resisting magnetic fields, as a bridge inspection drone will get close to big masses of metal elements e.g truss bridges.

Another issue is that almost all the drones in the market have a camera that is attached underneath of the drone, which limits its ability to look overhead, a major problem when carrying out bridge inspections.

Testing the efficiency of the tool

The Structural Assessment and Health Monitoring (SAHM) team at the Centre for Infrastructure Engineering (CIE), led by Dr Maria Rashidi, has collaborated with Road and Maritime Services RMS to trial remotely-piloted aircraft (RPA or drones) for bridge inspections.

As part of this feasibility study, qualified pilots from our team and RMS used a high-end drone to examine the effectiveness of RPAs for bridge inspection. Four bridges with various features and configurations have been tested to determine the efficiency of RPAs as bridge inspection tools. This research has already sparked interest across Australia, including other states’ transportation departments.

Drone images from multiple locations and point clouds can be used to construct 3D models using the photogrammetry tools and techniques. These drone models can be employed for virtual inspection and also as-built model development of bridges. Figure 2 shows the constructed point cloud of Cedar Point Bridge in NSW.

Figure 2. Point Cloud of Cedar Point Bridge.

Figure 2. Point Cloud of Cedar Point Bridge.

Faster and safer inspections than ever before

When comparing RPA inspections to conventional methods, one of the major benefits is the higher degree of safety. RPA inspections provide a mechanism that insure the bridge inspectors and the relevant crew aren’t exposed to higher risk situations.

RPAs today are capable of capturing images from under bridge regions without the need of man lifts and potentially closing down roads. This has dramatically increased the safety aspect of bridge inspections, as there are many risks that come into place when ropes and cherry pickers are used for underbridge inspections in conventional methods.

With the use of RPA’s technical abilities today, complex and large bridge inspections can be completed at a significantly faster time than conventional methods. For example, it only took 40 minutes to complete a full bridge inspection on the 116m long St Alban Bridge through the use of RPAs. The 40 minutes consisted of 18-minute setup time, 22-minutes flight.

Besides the safety and speed of operation, cost effectiveness is another advantage; many of the cost savings are associated with time reductions and safety. Our pilot study for large-scale bridges, showed that RPA inspection was 46 per cent faster and 61 per cent cheaper than the conventional inspection.

Remotely Piloted Aircrafts (RPAs) offer substantial potential in undertaking visual inspection with high accuracy and reduced risk to bridge crew, allowing bridges to be visually inspected without the need for inspectors to walk across the deck or utilise costly and often heavy underbridge inspection units.

This can significantly reduce the overall inspection costs and disruption caused to the general public. In addition to this, the use of air borne Aerial Photogrammetry enables asset managers and engineers to better understand a situation through the 3D spatial context offered by RPA systems.

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