Strainstall UK Ltd is a world leading specialist in load measurement and stress analysis with over 40 years of experience across all engineering disciplines. They also have many years of experience in the fields of highway and railway bridge engineering, and have developed a specific range of produces and services that are widely used by infrastructure and rolling stock managers to assist with monitoring and stress determination. The company has further expanded its portfolio of products by developing a cost effective system for determining when a bridge has been struck by a road vehicle and the severity of the strike.

The system is called Bridge StrikeAlert and involves the instrumentation of the bridge to obtain dynamic shock measurements. In the instance of a bridge with multiple decks, each deck can be independently monitored along with collision protection beams (CPB’s) if fitted. This ensures that in the event of a strike by a road vehicle, a rapid assessment can be made as to whether a CPB only has been struck and / or which deck. Depending on local procedures, this information can then be used in the decision making process as to individual lines being kept fully open or trains cautioned.

The system was developed due to the increasingly frequent reports describing delays to both road and rail traffic, following attempts by overheight vehicles to pass beneath low bridges. Due to the age of the railway network, many rail overbridges have limited headroom for today’s road vehicles making them susceptible to vehicle strikes. The disruption caused is not limited to the immediate problem of determining the safety of the structure and how soon the railway and highway can be reopened to traffic. The rail companies also have costs associated with the delays caused to trains, as well as for any repairs that are needed. Added to this, there is a suspicion that many bridge strikes go unreported. All this means that the rail companies in particular are keen to know what is happening at their problem bridges, in real time.

Following a strike, brief information is required immediately by the local signaller and by the infrastructure maintainers. The system has a number of automatic communication methods to alert the relevant personnel, which include both SMS text messaging and e-mail if required, along with a dial-up connection to allow a Structures Engineer to remotely view diagnostic screens to access the strike severity. A CCTV system can also be installed to aid identification of the vehicle that has caused the incident. This information may be used to pursue compensation claims.

The aim is to achieve wider network coverage of this type of system to cover a number of the most vulnerable bridges. It is envisaged that the system will act as deterrent, particularly to local haulage companies, by discouraging overheight vehicles from trying to pass under these bridges.

A system installed at a trial site and in operation for over a year has now captured a significant number of strikes by road vehicles and recorded the impact sequence / decks affected, severity of the strikes and digitally recorded the type of vehicle involved. In many of the strikes, the CPB’s have served the intended purpose by either fully eliminating or dramatically reducing the impact to the main bridge decks. Knowledge of this information immediately following a bridge strike can clearly play a key role in reducing the delays to both rail and road traffic.