I am building a model of a railway track on a bridge and I have used springs with remote connections to "stiff beams" which simulate the bridge deck. I have tried applying fixed supports on the bridge and also displacement with 0 in all X, Y, and Z, but the deformation of the rail seems to differ. In both cases, all parameters remain same except for the support condition to be either fixed or displacement supports.
1st picture is with fixed supports.
2nd picture is with displacement supports.
What is the reason for this?