Slab designs: Types and uses

Slab designs are an integral part of modern architecture, and they play a vital role in providing a strong foundation for buildings. The design of slabs depends on the type of building, the load they are going to carry, and the local environment. There are different types of slab designs such as one-way slab, two-way slab, waffle slab, flat slab, and post-tensioned slab.

Each design has its unique features, and they are used according to the specific requirements of a building. The primary objective of slab design is to provide stability, durability, and resistance to the structure. A well-designed slab can support heavy loads, provide thermal insulation, and enhance the aesthetic appeal of a building.

See also: Slab thickness: Importance and common mistakes done while determining slab thickness

8 slab designs

1. Two-way slab

Loads applied to the slab in two-way slabs are transmitted in both directions. Four corners of the slab are resting on the concrete beams or maybe on the steel or any other supports such as concrete walls.

These slab designs are more frequently used while building a structure. The slab typically ranges in thickness from 125 to 200 mm. In exceptional circumstances, these thicknesses might be raised as per the necessity of the structural design.

The slab will be designed based on the slab’s boundary condition and the moment and shear force coefficients supplied in the applicable standard. To find the bearing and shear forces in the slabs, computer modelling is another option.

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2. One way slab

Slab loads will be transported in a single direction only. The lengthier path will only transfer a small amount of weight. The beams around the short edges will support the loads in the slab.

Given that they only transfer loads in one direction, one-way slabs are less cost-effective than two-way slabs. Due to the one-way nature, people could be obliged to give a greater area of reinforcement and a thicker slab.

The design procedure is the same as for two-way slabs.

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3. Flat slab

The flat slab, as its name suggests, differs significantly from other varieties of slabs. The slab is not supported by any beams. Generally speaking, the slab’s bottom is flat, with a few abrasions.

Depending on the weights placed on the building, several types of flat slabs are built. A homogeneous thickness is never sufficient to support the imposed weight. In these situations, simply change the slab thickness where it is necessary.

• A flat slab is one with a constant thickness.
• Flat slab with drop panels- The slab thickness grows to a particular extent to carry the bending force and shear.
• Banded flat slab- A beam-like connection is made between the drop panels. Along the column strip, the slab’s thickness rises.
• Flat slab with column heads- The bending and shear forces are noticeably increased at column heads in a flat slab with columns. As a result, the area surrounding the column is widened.

A flat slab has the same load-transfer mechanism as standard one-way or two-way slab varieties. The column strip behaves like a beam, whereas the centre strip behaves like a typical slab.

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4. Waffle slab design

Waffle slab design is a reinforced concrete slab system that is used for large spans and heavy loads. The slab is designed with a pattern of ribs and deep square or rectangular cells, giving it a waffle-like appearance. The ribs and cells increase the stiffness and strength of the slab, allowing it to span longer distances without sagging.

Waffle slabs can be designed as one-way or two-way systems, depending on the direction of the load. The ribs and cells are reinforced with steel bars, which are placed in a grid pattern. The bars are placed at the bottom of the cells and the top of the ribs, and they are connected with stirrups to provide lateral support.

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5. Ribbed slab

Ribbed slab design is a type of reinforced concrete slab that has ribs on the underside. The ribs are used to increase the strength and stiffness of the slab, allowing it to span longer distances without sagging. The ribs are usually in a grid pattern, and they can be one-way or two-way systems depending on the direction of the load.

The main advantage of ribbed slab design is that it reduces the weight of the slab, making it more economical to construct. The ribs also create a space under the slab that can be used for mechanical and electrical services, reducing the need for suspended ceilings.

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6. Post tension slab

Post-tension slab design is a type of reinforced concrete slab that uses high-strength steel cables or tendons, which are tensioned after the concrete has been poured. The post-tensioning process involves placing the steel cables or tendons in the concrete forms before pouring the concrete. Once the concrete has hardened, the cables are tensioned with hydraulic jacks, creating a compressive force that counteracts the tensile forces in the slab.

The main advantage of post-tension slabs is that they require less concrete than conventional slabs, resulting in thinner and lighter slabs. They also provide greater flexibility in design, allowing for longer spans without the need for additional support structures.

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7. Cantilever slab

Cantilever slab design is a type of reinforced concrete slab that is supported on one end and projects horizontally into space. The unsupported end of the slab is called the cantilever, and it can be designed to extend overhangs, balconies, or roofs.

The design of a cantilever slab requires careful consideration of the load and forces that will act on the slab. The thickness of the slab, the reinforcing bar placement, and the depth of the cantilever are all important factors that must be taken into account.

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8. Composite slab

Composite slab design is a type of reinforced concrete slab that is designed to work in conjunction with steel beams. The steel beams and concrete slab are connected by shear connectors, which are usually welded studs. When the concrete is poured onto the steel beams, it bonds with the steel, creating a composite structure.

The main advantage of composite slab design is that it combines the best features of both steel and concrete. The steel beams provide strength and stiffness, while the concrete slab provides mass and durability. The combination of the two materials creates a structure that is stronger and lighter than either material on its own.

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