The flat plate is a two-way reinforced concrete framing system utilizing a slab of uniform thickness, the simplest of structural shapes.
Flat Plate System Introduction
A flat plate is a one- or two-way system usually supported directly on columns or load bearing walls. It is one of the most common forms of construction of floors in buildings. The principal feature of the flat plate floor is a uniform or near-uniform thickness with a flat soffit which requires only simple formwork and is easy to construct.
The floor allows great flexibility for locating horizontal services above a suspended ceiling or in a bulkhead. The economical span of a flat plate for low to medium loads is usually limited by the need to control long-term deflection and may need to be sensibly pre-cambered (not overdone) or prestressed.
An economical span for a reinforced flat plate is of the order of 6 to 8 m and for prestressed flat plates is in the range of 8 to 12 m. The span ‘L’ of a reinforced concrete flat-plate is approximately D x 28 for simply supported, D x 30 for an end span of a continuous system, to D x 32 for internal continuous spans.
The economical span of a flat plate can be extended by prestressing to approximately D x 30, D x 37 and D x 40 respectively, where D is the depth of slab.
Advantages of System:
- Simple formwork and suitable for direct fix or sprayed ceiling
- No beams—simplifying under-floor services
- Minimum structural depth and reduced floor-to floor height.
Disadvantages of System:
- Medium spans
- Limited lateral load capacity as part of a moment frame
- May need shear heads or shear reinforcement at the columns or larger columns for shear
- Long-term deflection may be controlling factor
- May not be suitable for supporting brittle (masonry) partitions
- May not be suitable for heavy loads.