A Flat slab is a two way reinforced concrete slab supported directly by RCC columns without the use of support beams. The shear load of the slab is directly transferred to the RCC column supports. The flat plate slab framing system provides slabs of uniform thickness. This system, either includes “ Drop Panels “ or “ Column Capitals” to resist heavy loads and allow longer spans. Drop panels are usually two times the thickness of slab or as per the design.
This type of slabs gives freedom to architects and designers to design with flexibility, and engineers the power of execution without much alteration. On the other hand, flat slabs are inexpensive to build and suitable for layouts like floors and curved shapes.
Benefits of using concrete flat slabs is to ease the construction process especially for installation procedures and saving on construction time. If the design permits, try to avoid drop panels as much as possible and make the best use of the thickness of concrete flat slabs. The reason is to avail the benefits of flat soffits and the floor surface to be maintained, if necessary by design, drop panels to be cast as part of the column. There are some essential design aspects to keep in mind are as under:
- Design Procedures
- Presence or absence of holes
- The Importance of deflections
- layout application experience
Types of Flat Slab Construction
There are Four Types of Flat Slab Construction
- Simple flat deck slab
- Slab with drop panels
- Slab with column heads
- Slab with both drop panels and column heads
Where to use Column heads or drop panels in flat slab?
We can use either column heads or drop panels in the following scenarios:
Uses of Column Heads
- Column heads increase shear strength of slab
- Column head reduces the slab clear span and reduces the moments in the slab.
Uses of Drop Panels
- Drop Panels increase shear strength of the slab.
- It increases the negative moment capacity of the slab.
- It solidifies the slab and reduces deflection in the flat slab.
Advantages of Flat Slabs
There are many advantages flat slabs have:
- Flat deck slabs can be built at a very fast pace with the drop panels because of simplified framework and structure.
- Adaptation of the concrete flat slab system can increase the clear height between the floors to allow the installation of services specially in the absence of the false ceiling.
- Flab slabs decrease the cost of installation of expensive ceilings and partition material.
- In case of low building height construction, flat deck slabs are ideal to adopt.
- Flat deck slab provides flexibility to the designers, architects and the clients to design according to the situation.
Thickness of flat slab
Minimum thickness of the flat surface slab is calculated as per the ACI 318 and IS 456 is 125mm. By implementing these standards, we can determine the thickness of the slab by the span.
Simply Supported Slab = Span / 20
One End Continuous Slab = Span / 24
Both End Continuous Slab = Span / 28
Cantilever = Span / 10
Types of Flat Slab Design
There are many methods to design flat surface slabs and evaluate these designs in flexures.
Some of these methods are as following:
- Empirical method
- Sub-frame method
- Yield line method
- Finite –element analysis
Benefits of Using Flat Slab Construction Method
- Flat slab provides more flexibility in the design of buildings to the architect. It allows the residents to change the size according to their requirements. Flab slab allows you to skip the false ceiling by providing just a skim coat and saving a lot of bucks.
- Building cost can be reduced by adopting flat slab construction, because of the flat surface, fewer columns and beams are required to be erected, thus cutting in construction cost. Building height is reduced as well and less will be spent on façade, partitions and finishing. Because of less building load, foundation sizes will also be reduced to small and approximately 10- 15% of structural cost can be reduced.
- Flat slabs require less time to erect as compared to the conventional slabs, because of the absence of a variety of beams and other structural members.
- MEP services are more easy to install on flat slabs as compared to the conventional slabs. Installations can be mounted directly on the slab without altercation and bending.
- We can use prefabricated mesh in the flab slabs to minimize the installation time. Prefabricated meshes are available in the standard sizes and dimensions and provide better quality control in the construction of flat slabs.
- We can get a better buildable score by adopting flat slab construction. Because we can use prefabricated structural members and integrate them into the design for ease of construction. This process makes the structure more buildable then the conventional ones, it also reduces the number of staff required on the site and increases their productivity by providing a higher tendency to achieve a better buildable score.