BS EN 1317 is a performance based standard that covers all Vehicle Restraint Systems including Safety Fences.
Beware - Don't be caught out with a nominally compliant system that is likely to fail in real life conditions, even when impacted under the same criteria that approved the product for use on the Highway.
When a parapet is specified the main criteria asked for is Containment Level i.e. N2. The second criteria to be specified which has been introduced by the European standard is Working Width i.e. W2. The Working Width relates to the distance between the front face of the vehicle restraint system prior to impact and the furthest lateral position of any major part of the system or vehicle during impact. Whilst the Working Width is required to be specified it really has little value with regard to parapets, as there are rarely obstacles behind a parapet system. Under the British standard BS 6779 a maximum wheel penetration of 500mm, which is taken from the outside face of either wheel, was specified. This ensured that the vehicle wheels would not leave the bridge under the criteria for which the parapet was designed. It is important to note that the British standard specified a test plinth size of 800mm minimum. This was specified in order to take secondary measurements of the wheel penetration from the tyre marks left on the plinth, the primary means of measuring wheel penetration being from an overhead camera.
The European standard does not specify a plinth size because the standard covers all vehicle restraint systems with Working Widths ranging from W1 = .6m up to W8 = 3.5m to accommodate safety fences (typically W4-W6). It is this criterion (Working Width) that allows approved parapet systems to be used on the highway that can fail in real life conditions. Unlike safety fences, bridge parapets are installed on the edge of a bridge structure on a typical plinth size of 450mm.
In order to demonstrate the possible deficiencies of a system tested on a 900mm plinth Varley and Gulliver carried out a (TB32) test on an aluminium parapet with a 1500Kg vehicle, using a conventional test plinth of 900mm wide as used under BS 6779. The parapet attained a working width of W3 with all other test criteria being met. Varley and Gulliver could have hidden behind the standard and now be supplying this BS EN 1317 compliant system worldwide. As a company we were concerned of the possible effects to the system when impacted on a 450mm plinth. Under
BS 6779 this test would have been a failure because the maximum wheel penetration was greater than 500mm.
Varley and Gulliver had the plinth modified to replicate as far as possible a bridge edge beam 450mm wide with a shear edge. The same parapet was then tested. Contrary to some views that there would be insufficient time for a vehicles unsupported wheels to drop and affect a systems performance, the vehicle wheels immediately dropped over the plinth causing the vehicle to roll which resulted in all pre impact posts being ripped off their bases, approximately 24m of parapet. THE SYSTEM FAILED.
This system passed on a test plinth size of 900mm wide, but failed on an actual bridge plinth size of 450mm.
COMPLIANCE WITH EN 1317 DOES NOT ENSURE PRODUCT PERFORMANCE IN THE LOCATION FOR WHICH IT WAS DESIGNED
When considering a bridge parapet Working Width should be considered along with Dynamic Deflection
Dynamic Deflection. The dynamic deflection is not required to be specified however during the approval test its measurement has to be taken. The Dynamic Deflection is the maximum lateral dynamic displacement of the front face of the vehicle restraint system. This can give you a guide as to whether the vehicle wheels will be off the bridge.
Be Safe - Be Sure
DO NOT PLACE A PARAPET ON A STRUCTURE WITH A PLINTH WIDTH LESS THAN WHAT IT WAS TESTED ON
EN 1317
Advice
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For a Presentation on
BS EN 1317
contact
sales@v-and-g.co.uk
Varley and Gulliver Ltd
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