The different support reactions at B and C

I know that pins prevent horizontal and vertical translation and that rollers prevent only the vertical one. Therefore, what I do not understand here is that while the support at B reacts with two forces C support has only one, even though both look like pins to me.Where am I going wrong here?

(I could not find anything on the site about whether I can upload images this way. I hope there are no copyright issues related to my post because I do not own the images. If there is, please notify me and I will immediately take them.)


It's simple: while B is a pinned support, C is a roller. You can see that in the figure, where B is drawn clearly bolted to the "ground" while C isn't. In fact, the contact between C and the "wall" seems to be a wheel of some sort.

Rollers don't have to "prevent only the vertical [translation]". They have to prevent translation in one direction while allowing it in another. The most common case of a roller is resting on a horizontal surface, therefore preventing vertical motion but allowing horizontal motion. In this case, however, the roller rests on a vertical surface, therefore horizontal movement is restricted but vertical movement is free.


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