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The method of analysis is similar regardless of the traffic direction (with one exception, as noted below). For all specifications, the program considers two, three and four adjacent vehicle lanes and selects the critical case. Appropriate lane reduction percentages are used for the three and four lane loading cases.
When the traffic direction is perpendicular, under Under the last paragraph of LRFD 3.6.1.2.6, if the live load and impact moment, based on the distribution of the wheel load through earth fills, exceeds the live load and impact moment calculated according to LRFD 4.6.2.10 (equivalent strip method for fills < 2 feet), the latter moment shall be used. Therefore, when the fill depth is greater than or equal to 2 feet, and the traffic direction is perpendicular, then Eriksson Culvert runs the moving live load analysis twice, one with the assigned fill depth, and once with a fill depth equal to 0.
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