Fourth power law
The fourth power law (also known as the fourth power rule ) states that the stress on a road by a motor vehicle is greater, the greater the axle load of the vehicle in question. The stress on the road increases proportionally to the fourth power of the axle load of the vehicle traveling on the road. This law was discovered in the course of a series of scientific experiments at the end of the 1950s in the United States and was decisive for the development of standard construction methods in road construction .
background
At the beginning of the 1950s, the American Association of State Highway Officials ( AASHO for short ) dealt with the question of how the size of the axle load affects the service life of a road pavement. For this purpose, a test track was built in Ottawa (Illinois) over several years , which consisted of six loops with two lanes each. The roadways were paved with both asphalt and concrete and in different thicknesses. During the two-year test series (so-called AASHO Road Test ), trucks with different axle loads then drove almost continuously on the test roads.
When evaluating the test series, it was found that there is a relationship between the thickness of the pavement, the number of load transfers and the axle load and that these have a direct effect on the service life and the state of use of a road. The service life of the road is reduced by roughly the fourth power of the axle load.
The accuracy of the fourth power law is controversial in the professional world, since the test results depend on the factors mentioned above and many other influences, such as climatic conditions.
Calculation example
A numerical example should illustrate how differently the above According to the law, a car and a truck affect the surface of a road.
- Passenger car (total weight 2 t, 2 axles): load per axle: 1 t
- Truck (total weight 30 t, 3 axles): load per axle: 10 t
The load on the road from one axle (2 wheels) is 10 times as high on a truck as on a car. The stress (damage) on the road by one vehicle axle is the above. However, according to a series of tests on the truck
- - times as big
as with the car. Because of the three axles of the truck, this value triples, but since the car has not just one but two axles, the comparison value is reduced by half again, so that the following difference in load results for both vehicles:
- Truck: car = 15,000: 1
This means that the car only causes as much damage after 15,000 passes as the truck does when driving on the road once. From this it can be deduced that a large part of the damage on the roads is caused by heavy goods vehicle traffic and that cars only contribute a very small part.
application
The AASHO Road Test has shown that the layer thickness of the road surface has a decisive effect on its service life. For this reason, standard designs were developed that can be used for different loads. In order to obtain a comparison of the individual vehicle types and their axle loads, these are converted to a 10-tonne axle. The resulting number of 10-tonne axle transitions ultimately determines the structure, which can be determined according to the guideline for the standardization of the superstructure of traffic areas (RStO).
See also
Web links
Individual evidence
- ↑ S. Velske, H. Mentlein: Road construction technology . Werner Verlag, Düsseldorf 2002, ISBN 3-8041-3875-6 , p. 4 .
- ↑ Influence of the longitudinal evenness of the road surface on the road load at RWTH Aachen University