Member article by ProDroneWorx:
Bridges are critical assets in the transport and infrastructure network, but they are also subject to ongoing wear and deterioration caused by traffic loading, weathering, corrosion, and environmental conditions. Regular inspections are essential for ensuring structural integrity and public safety. One of the most challenging aspects of bridge inspections is accessing the soffit areas and cross bracing between beams, which are often located in narrow, dark, and confined spaces beneath the deck.
Traditionally, these inspections require rope access technicians, scaffolding, underbridge units, or barges, all of which involve significant cost, time, and safety risks. Increasingly, confined space drones are transforming how engineers approach these tasks, offering safer, faster, and more comprehensive surveys of difficult-to-access areas.
The Challenge of Inspecting Soffit Cross Bracing
The soffit, the underside of the bridge deck, is a critical inspection area because it contains structural steel elements and cross bracing that provide stability to the beams. Over time, these components may develop:
- Corrosion and rusting due to water ingress or exposure to de-icing salts.
Fatigue cracking in welds and connections. - Paint and coating failures leading to accelerated deterioration.
- Loose or missing fixings at bolted joints.
Accessing these areas presents unique challenges:
- Restricted clearance between beams makes manoeuvring difficult for inspectors or equipment.
- Dark, dusty, and confined environments reduce visibility and increase hazards.
- High safety risk from working at height, over water, or in traffic management situations.
- Cost and disruption of traffic closures, scaffolding erection, or deploying underbridge units.
The Drone-Based Solution
Confined space drones, equipped with collision-tolerant cage, stabilisation system, integrated lighting, slam based laser scanner and high-resolution video are specifically designed for operating in these environments. By deploying drones into the soffit voids, inspection teams can capture high-resolution imagery and video of the cross bracing and connections without the need for physical access.
Key features that make confined space drones effective for soffit inspections include:
- Collision tolerance: Protective cages allow safe operation in narrow gaps between beams.
- Powerful onboard lighting: Illuminates dark soffit areas, eliminating the need for external lighting rigs.
- High-resolution cameras: Capture detailed images of corrosion, cracks, or joint conditions.
- Thermal imaging: Detects anomalies such as heat build-up from stressed joints.
- LiDAR or 3D mapping: Creates spatial models of the bracing for dimensional checks or digital twin integration.
Benefits of Drone Based Soffit Inspections
- Enhanced Safety – Removes the need for personnel to enter hazardous confined spaces or work at height, reducing risk of falls, accidents, and exposure to dust or contaminants.
- Operational Efficiency – Inspections that may take days with scaffolding or rope access can be completed in hours with drones, significantly reducing downtime and disruption.
- Cost Savings – Avoiding scaffolding, underbridge units, and traffic management leads to major cost reductions.
- Minimal Disruption – Drones can often be deployed without closing lanes or interrupting bridge operations, a major advantage in busy transport networks.
- Comprehensive Data Capture – Digital imagery and 3D models provide a permanent record, supporting ongoing asset management and predictive maintenance.
Real-World Application
ProDroneWorx confined space drone has been successfully deployed to inspect various features of bridges e.g.
- Soffit inspection of a bridge completed in under one day, compared to an estimated three days using scaffolding.
- Engineers were able to identify and document localised corrosion on bracing joints, supporting targeted repair rather than full-scale maintenance.
- The inspection was carried out with no lane closures, avoiding disruption to thousands of daily road users.
Bridge soffit cross-bracing is a vital structural element, but it is also one of the hardest to access using conventional inspection methods. Confined space drones provide a safer, faster, and more cost-effective solution, delivering detailed imagery and data while eliminating many of the risks associated with manual access.
As infrastructure managers face growing pressure to maintain ageing assets while reducing costs and disruption, drone technology is emerging as a powerful tool.
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(Image – ProDroneWorx)