Corus launches roadside restraint systems

Materials World magazine
1 Mar 2007
Barrier along road

International steel company Corus has launched a new range of roadside restraint systems that it claims exceeds the performance levels and test criteria stipulated by the European EN1317 standard.

Manufactured from rectangular hollow tubular sections and protected from corrosion through hot dip galvanisation, the Protect 365 family of products are designed to reduce the severity of road accidents caused by errant vehicles. They have been in development for four years and comprise a series of parapets for low and high risk areas, safety fences, and transitions for safe connections between parapets and fences.

Hitting hard

To comply with the European EN1317 standard, all such systems must undergo a crash test at the recommended impact points, performing against a 30t truck and a small 900kg car containing a fully instrumented crash dummy. The barriers must meet guidelines for impact severity on the vehicle body and in turn the occupant (accelerated severity index (ASI)). An ASI below 1.0 illustrates that the structure will have a low level of impact. Anything above 1.9 is considered too destructive to be viable.

The team at Corus, however, felt that this minimum assessment requirement did not ensure safety in all possible crash scenarios. Bill Russell, Market and Business Development Manager at Corus Tubes, says, 'Within our system, we go beyond that. We look back to certain elements that were [specified] in the previous British standard and use computer modelling for a "what if analysis", looking at the foreseeable worst case scenarios and designing around them.'

One example was the decision to conduct crash tests between the two extremes of the largest and smallest vehicles. Corus carried out an ASI assessment on a 1,500kg car. Russell adds, 'We felt that this was important as the majority of cars on Europe's roads today are in this mid-range weight category. The EN committee is now recommending this to other national bodies.'

Corus has combined standard finite element analysis software with a range of vehicle models to simulate the trials. The 1,500kg sample was adapted from a model orginally created by MG Rover, while digital replicas of the 30t truck were produced using 2006 data supplied by DAF Trucks UK. 'We are using up-todate vehicles, which is essential for accurate simulation rather than animation,' explains Russell. '[It is] more representative of on-the-road performance.'

Beyond the impact points outlined by EN1317, 'what if analysis' was employed by crashing the car along the length of the barrier, on its front and even in the opposite direction to traffic flow to identify weak spots. This was verified through on-the-road strain gauge analysis, with data fed back into the computer system.

Absorbing energy 

The benefits of this additional investigation were clear. When hitting the 1,500kg car against the barrier, Corus found that heightened impact energy caused increased deformation of the mounting brackets, resulting in unacceptable levels of impact severity on the vehicle and a need to redesign the structure.

‘We have tried to take energy out of the impact [by installing] energy absorbing steel brackets,' says Russell. This not only reduces the ASI figure through more controlled and progressive deformation of the barrier, but 'in the case of the parapets, there is also a lot less load on the bridge deck', aiding bridge engineers in their constructions.

Use your head

According to Corus Automotive engineers that worked on the project, the EN1317 standard also fails to acknowledge the importance of head impact criteria (HIC), which is a recognised safety benchmark for automotive manufacturers.

During crash tests, it was found that impact speeds exceeding 110km/h caused vehicle occupants' heads to come through the side window and strike the barrier. The simulated HIC value of 2,300 was far greater than the 1,000 value targetted by manufacturers.

Russell outlines the subsequent redesign of the Protect 365 range. 'We started off with a flat face system. Now we have introduced a "step" between the bottom and the top of the barrier. It is about 600mm high, so the vehicle hits the lower part of the system, but we have a safe haven allowing the occupant's head to come out of the window without [striking] the barrier.' Subsequent trials have shown a reduced HIC value of 107.

'Hopefully, [these findings] will influence how systems are designed in the future,' Russell adds.


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