Detection of bridge impact

Automated monitoring systems accelerate the response evaluations, help quantify the damage and enable identification of offending drivers for prosecution and recovery of costs

Bridgestrike

11 bridges monitored
Accelerometers used to detect impact
Video cameras record the incident before and after impact
Automated reporting
Notification direct to asset manager
On-line platform for reviewing data on network-wide map
Print-out report for ease of distribution

Bridge impact from over-height road vehicles is a persistent problem for bridges with low headroom across the London Underground network. Initiatives to warn drivers have reduced the frequency, but not eliminated the occurrences. Transport for London have chosen to take a combined approach of increasing driver awareness, use of collision protection beams and capturing evidence for prosecution of offending drivers.

London Underground installed three of JF Strainstall's BridgeStrike systems on bridges which were prone to impact and further expanded 18 months later, adding a further eight systems to other sites.

BridgeStrike constantly monitors each bridge for sudden movements, detecting the shock. By learning the normal behaviour, the differences between passing trains and actual impact can be distinguished. When a potential strike is identified by the algorithms, recordings of accelerometer measurements at critical positions and video evidence covering a period before and after the impact are captured.

Notification is sent automatically to the bridge manager(s) and a report is presented including images, assisting the speed of response to inspect and assess the bridge damage. The internet accessible platform, where all BridgeStrike monitored sites are visible along with their current status and history of previous impacts. The platform is accessible from any computer or internet connected device (mobile phone/tablet).

The data recorded has proven successful for the prosecution of drivers and continues to improve the awareness for high vehicle drivers and their employers.

Bridgestrike

Installation

The implementation of the systems was managed by JF Strainstall, including planning, installation and continued operation and maintenance for multiple years. JF Strainstall installed the most recent eight systems by a turn-key approach, responsible as Principal Contractor, providing the planning applications, traffic management, and plant for access at height.

Holding safety at the core of both JF Strainstall and Transport for London, we collaborated in

“Throughout the installation of all systems on all assets, JF Strainstall have shown a high standard of compliance in their safety documentation and site teams.” Paul Wilkinson, Senior Construction Supervisor TfL

developing site safety documentation that satisfied the needs of all and simplified the actions for controlling, checking and reporting the works.

Innovations

JF Strainstall worked with London Underground to further develop the functions of BridgeStrike for the implementation of the later eight installations, including a custom dashboard to display the vital information in an easily readable format. Enhancements were discussed and those most useful for the management of these bridges were implemented. Some bridges have added displacement sensors to detect global movements of the superstructures which confirm bearing offsets caused directly by vehicle impact.

The automated post-processing has added functionality in which the data collected is analysed to quantify the energy magnitude of impact sustained by the structure. As data is collected on previous impacts this will help inform the bridge managers of the likelihood of damage sustained. If an impact is of less energy than those previously experienced, then detrimental damage is less likely and the structure might remain open, even before site inspection can be conducted.

Some potential impacts detected and recorded are identified as being caused by passing trains. The patterns in these are being used to detect wheel-flats of the trains.