The investigated methods are substantially limited, in the case of direct securing, to introducing the maximum loading capacity of the securing devices into the balance, while in the case of frictional securing (tie down lashing) the vertical components of the nominal pretension of the lashings are used. Short comings in direct securing are that the cargo movements necessary for developing the force in the securing devices do not appear in any form, not even as a warning, in the regulatory texts and the shortfalls in securing arising from the different load deformation behavior of securing devices arranged in parallel are also not mentioned. With few exceptions, the horizontal components of tie-down lashings arising from frictional engagement are ignored. They are introduced statically into the test of securing against tipping, in order to take account of the k-factor which had in the meantime been recognized as important. This k-factor takes account of the known circumstance of friction of a lashing at the cargo edges and thus of impaired pre-tensioning if, as is customary, only one side is pre-tensioned. However, for reasons which are not publicly known, the k-factor was dropped again from the later draft would seem to have been replaced by a half-hearted safety factor.
The k-factor is certainly justified and important as an expression of general weakening of the tie-down lashing principle in the case of a one-sided tensioning device. The stated sources make no meaningful interpretation and use of the underlying causes because there was a desire for simple formulae and there was therefore no willingness to take account of the laws of force and deformation.
Cargo movement and deformation of securing devices Direct securing, which is justifiably regarded as highly effective, inevitably involves movement and/or deformation of the cargo. However, tolerable limits for such movement or deformation are not specified anywhere. They nevertheless exist and agreement should be reached. It would then, however, be consistent to allow the same movement latitude to tied-down cargo units. The potential of frictional securing, which is itself associated with drawbacks, could be further exploited as a consequence.
The deformation brought about by development of force in portable securing devices may straightforwardly be calculated with sufficient reliability. Obtaining comparable data for fixed fittings and attachments on loading areas, such as sidewalls, end walls and stanchions is problematic. Inquires may be made of the vehicle manufacturers.
Taking account of cargo movement and deformation of securing means, the calculation of which has been demonstrated in a number of examples, demonstrates the worrying order of magnitude of the above stated shortcomings in conventional calculation methods in both the positive and the negative direction.
The objective cannot be to replace the conventional, relatively simple formulae which can be presented in tabular form for dimensioning sufficient securing effort with more complicated calculations, at least not for day to day use. The obvious conclusions must, however, be drawn. In so doing, all the advantages of the extended approach should be used. It must thus already be acknowledged that the tie-down lashing principle will benefit. Its reputation is enhanced and lashing requirements may be reduced to what is physically justifiable. It is as yet unclear which new formulae and associated constraints may be used to achieve this objective.
A similar situation may apply to direct securing, if certain physical laws are more effectively applied than in the past. However, the homogeneity of securing arrangements, i.e. uniform load deformation behavior and limitation of cargo movement may also give rise to restrictions. Similar approaches to calculation which are yet to be developed may also be applied to compaction, i.e. bundling and strapping, and enable economically attractive securing systems.
Ultimately, there must be simple, practical and legally reliable rules and guidelines, which may be applied while taking the fullest possible account of the underlying physical phenomena.
