API 1102 for railroad crossing program is based on the design methodology that has been used in analyzing existing uncased pipelines and designing new uncased pipelines that cross beneath railroads. This API design methodology relates to the train engine (E-80) which is the heaviest load:
- Steel pipelines installed using trenchless construction methods, such as auger boring, with the crossing perpendicular to the railroad.
- Pipelines having diameters 2 to 42 inches (51 to 1067 mm) can be analyzed.
- The wall thickness to diameter ratios must be within the range of tw/D = 0.01 to 0.08.
- Railroad crossings can be analyzed for depths of cover of 6 to 14 feet (1.8 to 4.3 meters).
- The loading condition for railroads is based for four axles distributed to the track surface
- Develops from the trailing and leading axles sets form sequential cars.
E-80 Design
The key phrase to understanding this is “the entire load shall be taken as distributed uniformly on the surface”. The method is to take the maximum axle load and distribute it in the longitudinal direction by the axle spacing. For a standard E-80 design that would be 80k / 5 ft = 16k/ft. Assume an 8′ long tie to make it easy and you end up with a 2 ksf surcharge at the bottom of the tie. The surcharge load will be 8′ wide and infinitely long. The surcharge load for the lighter axles are further away from the heavy axles.
E-90 Design
The E-90 Train Engine is the heaviest Train Engine made in the world. However, there is no specific documentation for this train engine by any agency. The Railroad (AREMA Manual -5,000 pages) does not give a specific reference because there are very few of these train engines made and running. Therefore, a simple ratio calculation is used to calculate the applied design surface pressure.
Calculation for E-90 is as follows:
Cooper E-90 = Cooper E-80 x 9/8Co the variable “w” in API 1102 would be equal to: 13.9psi x 9/8 = 15.74 psi