Railroad Crossing Calculation per API RP 1102

[yurikatchan]

I am preparing a spreadsheet for Railroad calculation per API RP 1102. Railroad Cyclic Stresses (circumferential and Longitudinal) are calculated as an applied design surface pressure multiplied by Factors (Stiffness, Geometry, Impact, and Single or Double Track). The design curves in API RP 1102 to determine the Factors are pretty much straight forward except the one for Double Track Factor. The double track factors are increasing when pipe depth of cover is increasing (figures 10 and 13). Does anyone has an explanation? I am pretty sure that there is a simple explanation since the calculated stresses are decreasing with depth of cover increasing, but I don't feel a sense of why the double track factors are increasing.

 

[BigInch]

Possibly because the distance between the tracks. At shallow depths only the load from one track affects the pipe directly below, however at deeper depths there may be a combined influence due to both tracks, where loads from each track are added together to affect pipe in the central region. Not sure.

 

[robyengIT]

BigInch is correct. Similar explanation you can find in site of American Concrete Pipe Association (

http://www.concrete-pipe.org)

where you can download the manual "Concrete Pipe design Manual" and see the theory in Chapter 4

 

[yurikatchan]

BigInch and robyengIT thank you very much for your help.