When there is upper floor or wall or column or any other type of load is acting on the slab corners are free to lift up when load is applied at slab’s center, This condition is known as slab corner are not held down.
When there is no such type of load is acting on slab corners then the slab This generally occur with one storied building.
it’s called as slab corners are held down i.e. slab corners are not allowed to lift up because of those load.
Many of the students it is quite difficult to visualize the torsion in a slab system.