The following should be treated as general guidance only.  
The uniformly distributed and concentrated design loads for floors and stairtreads should be determined from BS EN 1991: Part 1.  

For domestic glass floors, up to 2.5 m², the preferred general glass specification is for 3 panes of 10 mm Pilkington Optifloat™ T, laminated together and suitably supported along all four edges. 

Consideration must be given to the surface finish of the glass and to weight and handling issues. 

For commercial applications, please refer to BS EN 1991: Part 1 and provide loads and sizes to our Technical team, who may be able to assist you.