Photo of the month – April 2012 [German version]

To the fore!

This vehicle had to brake to slow down for traffic on the motorway. To be honest, that shouldn’t have been a big deal. But the state of the vehicle after this braking maneuver leads to the inevitable conclusion that the maneuver was anything but normal; or are we dealing with the laws of physics here?

Figure 1  [Geert Frans]

The vehicle is a perfectly normal curtainsider. We have no information about the strength of the superstructure, so we shall assume that the end wall had a securing capacity of 5000 daN. The load securing capacity available to the sides is of no relevance in this case, because the gap between the load block and the curtain is too large.

Figure 2  [Geert Frans]

The vehicle is loaded with 24 tonnes of cellulose. According to the statements that we have available, the load block had been loaded as a tight fit to the end wall. There is no sign of any load securing measures. When the driver was interviewed, he is reported to have said that the load is so heavy that it should not (theoretically) have been possible for it to move. As a pretty experienced load-securing columnist, it would be easy to pigeonhole this case and allow free rein to ridicule and derision.

But sadly, this issue (the weight of the load and its apparent inability to slip) is far too serious. So where does this "superstition" come from? Quite simply, people find it very difficult to imagine that heavy weights that would be in possible for a single person or even for four or five people to move are able to move on their own.

Figure 3  [Geert Frans]

Unfortunately, the photographs are not particularly clear, but they are adequate to illustrate the problem. The load of cellulose, that was packaged in "rough paper", has a coefficient of friction μ of no more than 0.3. If the end wall actually provided 5000 daN of securing force, there was a shortfall of 7000 daN of securing force to the front. This simple calculation only applies, however, if the entire load block was actually loaded as a tight fit in itself and as a tight fit to the end wall. If this is not the case, dynamic effects must also be taken into account that generate energy which must also be absorbed when the load comes into contact with the end wall.

In this particular case, it is clear that the securing was insufficient. The end wall initially became deformed and then became detached across the entire width of the loading area. The load block was finally stopped by the driver’s cab.

Figure 4  [Geert Frans]