1) Solid slab
The span of precast solid slab shall not exceed 2．4m；; Prestressed members, the span can reach 2.7m.
2) Trough slab
Because of ribs, the allowable span can be larger.
when the rib is under the plate, it is called a positive grooved plate. The stress of the slotted plate is reasonable.
3) Hollow slab
The economical span is 2.4-4.2m..