# How to get the most critical position of the load train in traffic loader

How could I get the most unfavorable loading with the NBR 7188 (brazilian code) load train? I’ve been testing a lot of options, but I think the software isn’t moving the load train in the transverse direction to get the most unfavorable forces.

My superstructure has 12,20 meters of width for the vehicle to move and I’ve tried setting only one notional lane (of width of 12,20 meters) and put the load train so it could move freely inside this notional lane, but it doesn’t seem to be how the module works, as it seems that the vehicle isn’t moving along the superstructure width to get the most unfavorable case to get the maximum values of the forces;

Another try was to set notional lanes with 3 meters of width and put the load train in each of them (my bridge has 12.2 meters of width in which the vehicle can move and the load train has 3 m of width); although it does get to a more approximate result, it doesn’t seem that the program is getting the most unfavourable forces for that load train — it seems that the program is just taking the most unfavourable case between the 4 cases that I set (the load train moving in each of the notional lanes that I tried), and not the location that causes the most unfavorable forces in beam elements. What is the correct workflow for that case? The second try is attached. Note that the distribution of loads of the brazilian load train differs from the eurocode.

In this annex I have the analytical solution for the position of the load train that causes the most unfavorable forces for the extreme girders of my superstructure.

Hello

The load train moves within the defined lane in longitudinal and transversal direction. Keep in mind, that the load train doesn’t cross the lane. Therefore you have to define multiple cases for every lane. In order to get the maximal inner forces you have to combine all of the different cases.

The general traffic loader workflow is described within our online bridge tutorial.

Best regards
Frederik Höller

But if I have defined a lane with 12,20 meters and the vehicle has 3 meters of width, Traffic Loader won’t move the load train within this lane in the transversal direction, as I mentioned, will it (I saw that the software has the option, in the evaluation tab, to switch the load train to move outside the lane)? Because the forces that it provokes on the beam elements aren’t comparable with the analytical solution as I noted. So, in order to get the maximum inner forces, I must work with combinations?

I don’t quite understand the multiple cases for every lane that you mentioned.