What are acceptable anchorage points for seatbelts on monocoque chassis? |
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In all cases the manufacturer of the kit car should either provide adequate seatbelt mounting points in the structure of the car or at very least guide you in the best and safest method of mounting your seatbelts.
Below are also some points VOSA have on the subject which will hopefully provide a good understanding of what the examiner will be looking for.
ALL VEHICLES
What to look for:
• Evidence that anchorages in a vehicle of the same, or a very similar type have been subjected to a seatbelt anchorage strength test to "European Standards" by a recognised
authority. This may be acceptable where there is clear evidence that the structure is identical
to the vehicle originally tested.
• Welding should appear neat and of good quality; whilst it is impossible to judge the
quality of a weld just by looking at it, messy welding is rarely strong welding.
• Bolts used in structural areas should be of grade 8.8 or better. Such bolts will be marked
8.8 or 12.9 on the hexagonal head, however, cap-head bolts or 7/16" UNF seat belt anchorage bolts (with an anodised finish} not marked in this way may normally be considered to be of equivalent strength. Bolts should be M8 or larger.
• Threaded bushes should be welded (at both ends} through the tube, and not end mounted on the surface. (A threaded bush may be attached by its side surface to a structural component} See Fig below:
 Cause for Concern:
• Welds of poor appearance, gaps or visible lack of penetration.
• Anchorages in thin and/or flat panels with little stiffness or re-inforcing structure or in thin walled tube.
• Low grade bolts (less than grade 8.8}.
• Insufficient bolt capacity, eg number of bolts and/or diameter of bolts.
 2i. Steel Monocoques
What to look for:
• Structural box sections.
2ii. Composite Monocoques.
Composite materials such as glass re-inforced plastic (GRP - also known as fibreglass) are fairly common in the specialist vehicle industry.
What to look for:
• Box Sections with heavy lay up (i.e. material thickness} .
• Re-inforced areas, for example using folded metal box sections laminated into the vehicle structure.
• Material lay-up of good quality with absence of air bubbles. • 7/16" UNF threaded fixing of suitable surface area, or welded to a spreader plate of suitable surface area. Cause for concern:
• Threaded fixing/spreader plate of insufficient surface area.
• Threaded fixing and/or spreader plate only retained by a thin layer of laminate on the outer surface of the structure.
• Material lay-up poor with obvious air bubbles or delamination (separation of material layers}.
• Cracking or flexing of structural areas.
• Loads from anchorages being transmitted to weak areas of vehicle. |
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