I think they usually use several layers of thick glass for these floors, so even if you dropped a coffee mug on the glass and it broke, there should be several more layers under it that should still be plenty strong to support your weight. Also I don’t think glass experiences bending stress the same way metal does, where it gets most of its damage from impact fractures. Meaning you can bend glass a lot and it won’t change, but if you introduce micro fractures it can weaken considerably. So an engineer would probably consider the first sheet of glass as sacrificial.

Been a long time since I read about this stuff though, would love input from someone better read.