What is a Concealed Beam (Hidden Beam)?

Concealed beams, also known as hidden beams, are structural elements embedded within the depth of reinforced concrete slabs. Unlike traditional exposed beams, concealed beams have the same thickness as the adjacent slabs and remain unseen after being filled with concrete. These beams are typically used in flat slabs and serve specific purposes.

Why Are Concealed Beams Used?

1. Uniform Aesthetics: Concealed beams enhance the visual appeal of a structure by maintaining a consistent slab depth without any irregularities caused by protruding beams.
2. Cost Savings: By eliminating the need for visible beams, formwork costs associated with beam construction can be reduced.
3. Structural Considerations: Concealed beams provide additional reinforcement along specific areas of a floor slab, especially near columns. This reinforcement helps distribute loads and prevent localized weaknesses.

Important Points to Note:

• No Such Thing as “Council Beam”: The term “council beam” does not exist in engineering. Concealed beams are established by reinforcing the slab along the line where an actual beam would be present.
• Minimum Roof Thickness: Concealed beams should not be used in roofs with a thickness less than 200 mm (approximately 7.85 inches).

Reasons for Using Concealed Beams:

1. Column Strip Strength: Concealed beams reinforce the slab in areas weakened by column strips.
2. Earthquake Resistance: They reduce the risk of shear failure and sandwiching during seismic events.
3. Reinforcement Limit: When the reinforcement in concrete beams exceeds 2% of the total reinforced concrete (RCC) volume, concealed beams offer an alternative.
4. Lateral Load Limitation: Concealed beams cannot effectively resist lateral loads.
5. Axial Load Capacity: Concealed beams can carry approximately 10% less axial load than normal exposed beams.
6. Vertical Displacement: Concealed beams exhibit 10% more vertical displacement than standard beams, making them relatively weaker in this aspect.
7. Concrete Placement: Excessive steel reinforcement (more than 2%) can hinder proper concrete placement, resulting in honeycombing.

However, it’s essential to recognize that concealed beams may not perform as effectively as standard exposed beams. Awareness and understanding of these factors are crucial when considering such construction methods.