How can I find the position of vehicle for maximum and minimum moving load cases?  How can I define moving step distance of the vehicle? How can I visualize the deflection/bending at each moving step? 

In MIDAS we can use the Moving Load Tracer to obtain the worst position of the traffic load for a given effect.

Depending on the effect that we are interested (i.e. reaction, beam force, etc.) we can choose the appropriate case and visualise the traffic load. For example, for the maximum bending moment of one of the mid-span members of the deck we can see this traffic distribution:

And for the reaction in one of the supports we can see this traffic distribution:

For each of these, we can export the traffic load layout as a Static Load Case using the "Write Min/Max Load to File" in the Moving Load Tracer function:

This will export an *.MCT" file which we can then run in the Tools >> MCT Command Shell unction in order to create the Static Loads. We then analyse the model again and we can check the critical load cases which we have exported as a Static Load Case for which we can check forces, displacement, etc. as we can for any other load case: