Those odd looking security barriers

You’ve probably seen these dotted around a few places, what looks like some sort of security barrier, but wondered how such an odd thing could work. Does something rise up from under the plate, are the walls active in someway, just what does it do?In fact, the function is pretty much the same as bollards that are fixed into the ground, to stop a road impact, just without the hassle of digging deep holes in the ground or ripping up the pavement.
Bollards, once basically a heavy metal tube a