Number of lanes according to EuroCode

Hello everyone,

I’ve been working with the Ella module and I’ve noticed an issue with Sofistik’s calculation of the number of lanes according to Eurocode. I’ve attached two images for reference. In the first image, we have a width of 12 meters and 4 lanes, which is correct according to Eurocode (nlanes = int(w/3) = 12/3 = 4).

However, in the second image, we have a width of 13 meters. According to the same calculation, we should have 4 lanes (13/3 = 4.33 → rounded down to 4). Yet, Sofistik calculates only 3 lanes. This discrepancy seems contradictory to Eurocode and doesn’t make sense. How is it that with 12 meters we have 4 lanes, but with 13 meters we suddenly have 3 lanes?

Can anyone please help me understand this?

Thanks in advance.

Try choosing an alignment other than “center”

Hi, thank you for your response.

Indeed, you are correct that when selecting either the right or left option, Sofistik accurately calculates the number of lanes. However, in my opinion, the most common configuration involves placing the lanes in the center, thereby leaving the remaining space on both sides. Could this possibly be a bug in the program?

No, it’s not a bug.

You have to actively choose the decisive lane configuration for your structure and which part you’re designing.

Most of the time it should be along an edge.
This will yield the most reinforcement in a plate (near the free edge) and will also give you the decisive placement for groundworks (max overturning moment).

Only in a few cases will a centric traffic placement be governing (e.g. max pos moment in a plate supported by two longitudinal girders)

Hello, thank you for your response,

I agree that the design would be done as you mention, but I think it’s calculated somewhat chaotically because in cases where there is an exact division, for example w = 12 → nlanes = 4, this wouldn’t be a centered case because only 3 out of the 4 lanes would have load.


Therefore, it would be dimensioned for overturning moment, and there would be no possibility of obtaining the maximum bending moment, even if you had a bridge deck with a dimension of 12 meters, for example.

I believe there should always be 3 lanes for the centered case (which I see as logical for design purposes, although it doesn’t strictly adhere to the Eurocode), or they should calculate according to the Eurocode, but I think they are doing a mix, where ultimately you dimension for bending moment or torsion depending on whether your deck has decimals or not, not based on your choice.

Thank you,

Best regards,