Berry Systems, Safety Barriers and Safety Rails

This states quite simply and clearly that barriers must be fitted to the edge of any building with vehicular access and these barriers must have an impact height of at least 375mm and be capable of withstanding the forces set out in BS 6399.

The British Standard defines the way to calculate the horizontal force required to be withstood by a vehicle barrier: F = 0.5mv²/(δc + δb)where m is the gross vehicle weight (in kilos), v is the velocity of the vehicle in metres per second. δc is the deformation of the vehicle and δb the deflection of the barrier. In practical terms for car parks, for vehicles under 2500kg - i.e. cars - m can be taken as 1500kg, v is taken to be 4.5 metres per second (10mph). In the absence of better evidence the deformation of the vehicle, δc, is taken to be 100mm and, for a rigid barrier the deflection is assumed to be zero. If these values are applied to the formula, F =150kN.

BS 6399 also states that, for cars, the force acts at 375mm above the floor (assumed bumper height) is distributed over a length of 1.5metres. Where there is a normal perimeter edge or half-level edge the 150kN force applies. But, where vehicles are travelling on a confined ramp – and cannot possibly impact the sides of the ramp structure at 90 degrees, then the requirement allows for "half force" i.e. 75kN. Where there is a perimeter edge opposite a down ramp which exceeds 20m in length, then a double or "twice force" barrier will be required i.e 300kN. (See Figure 1,).

This is the code of practice for barriers in and about buildings. It slightly pre-dates BS 6399 but states that barriers are required where there is a drop greater than

380mm. It further requires that, if these are in areas used by pedestrians, handrails and infill panels are required at a height of 1100mm and no gaps are allowed through which a sphere 100mm diameter can pass. BS 6180 also defines a load requirement of 1.5kN/m2 on the handrails and infill panels with a similar point loading on the handrail of 1.5kN. Therefore, a vehicle impact barrier needs to absorb a force 66 times greater than a pedestrian handrail rail system.

Reports have also been published by the Institution of Structural Engineers (ISE) and the Institute of Civil Engineers (ICE). Between them they have recommended:

Vehicle impact height be increased from 375mm to 445mm centre height - This was to allow for changes in vehicle designs and fashions.

Any rail edge less than 550mm from floor level be considered a step up point and that the 1100mm handrail height be taken from this point unless footholds can be spoiled - The ‘climb assist’ rule.

Where the approach to a barrier is greater than 20 metres, typically at aisle ends, a ‘twice force’ barrier is required. (See Figure 1).

Designers and operators should recognise the need to consider temporary or permanent changes to traffic flow.

A CPD Seminar is available entitled 'The Design and Installation of Vehicle Barriers in Off Highway Applications". This material has been approved by the RIBA and is intended for presentation to Architects and Engineers. If you are interested in participating in this seminar please call 01902 491100 or email sales@berrysystems.co.uk

All Berry Systems vehicle barriers have been tested at MIRA and by other independent consultants to ensure they comply with the relevant standards and recommendations. Copies of test certificates and reports are available on request.