Why is the unit load facing upwards? Flexibility/Force Method

Question

I used the flexibility method to solve questions like this, so I know you have to have a primary and secondary structure. My primary structure looks like this:

So if I apply my virtual load, I got this:

However the answer shows that the virtual load points upwards, opposed to my one which is facing downwards. The part I am confused about is in another question of mine, specifically this one:

where the Primary structure and Virtual load structure looked like this:

As you can see, my Virtual load is also pointing downwards in this scenario, however, it was correct for it to face downwards in this one, but it was incorrect for me to face my virtual load down in the first scenario. I want to know why, and how do I know which way to face my virtual load.

Answer 1

I prefer to call this method the "displacement compatibility" method, or less elegantly, the "close the gap" method.

As the above names suggest, actually, the direction of the dummy/unit load does not matter, it is placed upward to find the rate of displacement it causes (to close the gap), and the reaction, in the same direction of the dummy load, is then figured out by proportion.

On the other hand, the dummy load is placed downward to find the rate of displacement it causes (to produce the gap), then by the method of proportion, an equivalent load required to produce the gap can be placed at the location of the dummy load. The equivalent load is essentially the reaction required to close the gap from the reverse direction.