5  Summary, outlook and objectives

5.3  Conventional balance calculation methods

The analysis of conventional calculation methods compares and comments upon the following sources: VDI 2700, Sheet 2, November 2002, draft DIN EN 12195-1, April 2004, and draft DIN EN 12195-1, January 2009.

Some shortcomings and also errors were identified. 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. Shortcomings 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 draft DIN EN 12195-1 of April 2004, 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known, the k-factor was dropped again from the later draft of DIN EN 12195-1 of January 2009 and would seem to have been replaced by a half-hearted safety factor.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.