To be honest, I don’t even know how to do it.
If you be so kind, can you download the mesh from one of the links and see if it got something wrong? It’s just 86 kbp, a very simple bridge I made in 3dsmax 2015.
Since the bridge will only have one color on it (not even a proper texture) I am not really concerned about it. Though I would like to get some help about it reglardless so I can learn what I have done wrong with it. 