A High Court ruling that a grp tank which collapsed
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in a roll-over accident was defectively designed has raised a number ol questions about structure of lorries and passenger safety. The Structural Design Group at the Cranfield Institute of Technology has been investigating the implications by Graham Montgomeri
IE INTEGRITY of a bus or lorry .ucture in a roll over accident an emotive issue and tends to t a lot of publicity in the daily ass when such an accident curs.
[he ruling given by a High urt judge reported in CM Jgust 8) raised serious quesns about the liability for occunt protection in articulated hides according to the .uctural Design Group at the anfield Institute of Techlogy, part of the Vehicle Imt Centre and set up at the -tool of Automotive Studies as esult of a £120,000 grant from !Wolfson Foundation.
The judge ruled that the glass Tforced plastic tank was delively designed and collapsed a roll-over accident causing roof of the tractive unit to be tened.
;ranfield asks if this ruling im3S that the designers of tanker ni-trailers must ensure that y are self-supporting in any ;ition during an accident.
iome completely flexible lks have been designed. ?Jse tanks are carried on a flat trailer and have a lower centre of gravity than many rigid tanks. But can they be said to be immune from roll-over and, if they are not, should they be provided with a protective structure at the headboard?
Cranfield takes the argument further and suggests that most tilt covered trailers and many with curtain sides have a very light structure which would do little to protect the tractive unit occupants in the event of rollover. Flat bed artic roll-overs are not unknown and what is their position in the light of this ruling asks the SDG?
There is no current legislation calling for roll-over protection in the cabs although EEC Regulation no 29 provides for a static loading on the roof equal to the front axle weight. According to the SDG, experience with the bus roll-over problem would indicate that this regulation will not prevent the collapse of the cab structure when submitted to a horizontal load at roof level.
During investigations into psv accidents, it was found that a structure which would not deflect if the vehicle landed on its roof without a side load would be flattened to the waist-rail in a true roll-over accident where the cant rail suffered a horizontal impact. The SDG argues that lorry cabs built to the Swedish regulations are likely to be much better in this respect.
The illustration shows that a large deflection of the cab superstructure when subjected to the Swedish case of an impact on the A-post involves the same number of plastic or collapse hinges as would a side or even a frontal horizontal impact at roof level. The SDG claims that this statement is still conjecture since no attempt has yet been made to quantify the horizontal load (or the energy involved in an impact) on the roof to which the cab must be designed to provide adequate crew protection.
The Structural Design Group argues that it is reasonable to assume that, if cabs are not to be made stronger, trailers should provide some protective strength for the crew.
The SDG at Cranfield has considerable experience in this type of accident protection. The group assisted in the design of the HCB Angus fire tender, where it is known that at least one of these vehicles has survived a roll-over accident with minimal crew injury, and has been the prime contractor in the coach roll-over investigation carried out for the Department of Transport.
Other roll-over protective structures for agricultural tractors and passenger cars have also been designed or analysed by the group.
The SDG uses a combination of theory and test as far as is possible in this work and has proved, in the case of psv structures made of rectangular steel tube, that the roll-over be
haviour can be predicted theoretically with great accuracy.
The main computer program used, Cranfield Structural High Deformation (CRASHD) was developed with the support of the Department of Transport to comply with the proposed regulation regarding bus strength of superstructure which will allow type approval by calculation.
Type approval will only be given if an approved program is used which allows the collapse characteristics of the structural elements to be simulated and Cranfield claims that CRASHD is almost certainly the simplest and cheapest program which will do this. The program can also be used for any cab structure or trailer framework which may be designed to pro vide roll-over protection. In the case of the trailer, a new optimisation program called WEST is available which will automatically choose the lightest or the cheapest square or rectangular section tubing for such a protective structure.
For the special case of grp structures, or those made of any composites, the SDG is negotiating a licensing agreement with Merlin Technology of California to use their ARGUS program which is able to calculate the effects of impacts on such structures.
The SDG suggests that it is probable that most box-type semi-trailers made of steel or aluminium are adequately stiff for cab protection in a pure rollover but this may not be the case for grp designs and ARGL would allow these cases to I checked.
Cranfield agrees with the COT merit made by the judge th "inadequate research had be carried out as to the cons quences of roll-over accidents It has taken more than five yea' research, much of it intern tional, to establish the mc likely form of coach roll-over al then to draft a regulation to pr vide improved passenger pr tecti on.
Although Cranfield does n suggest that such a comprehe sive programme of work shot. be undertaken for artics, it do claim that there are sevel areas where research cou prove Valuable: • a more thorough examinati. of the dynamics of artics establish the conditions unc which roll-over may take place • the extension of accidE simulation programs that ha been developed for psv and car side impacts to art ulated vehicle roll over.
• an examination of accidE investigation data to determi the most likely form of structu crushing of lorry cabs (fore a aft or lateral).
• an examination of the mc cost and weight effective way provide greater crew safe whether it should be by tracti unit or trailer structural stiff( ing.