Reinforcement Detailing of Concrete Slab Openings (Cutouts)

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Many times openings (cutouts) are required to be provided in reinforced concrete slab in buildings to provide way for lifts, or cables, ducts or other instrument to pass through one floor to other floors, mainly in the case of industrial buildings. But in that case, special care need to be taken while detailing of reinforcement for such openings in slabs.

Detailing of Concrete Slab Openings (Cutouts)

Detailing of opening in slabs is based on factors like size of opening, loads on slabs, floor vibrations etc. In the case of large openings it is desirable to place beams under the opening area so that no additional detailing of slab reinforcement is needed and load is directly transferred to main beams through secondary beams.

1. Detailing of Small opening in slabs

Where openings are small and are less than 150mm in larger dimension, with no special loading or vibration condition of slabs, following type of detailing should be done:

Fig: Detailing of small slab openings

For Holes less than 150mm, reinforcement bars may be displaced, additional reinforcement is not required.

2. Detailing of Slab openings of 150mm to 450mm

For slabs with openings more than 150mm and less 450mm, at least one half the quantity of main steel reinforcement intersected by the opening is provided parallel to the main reinforcement bars on each side of the opening extending a length of development length L_d beyond edges of the opening as shown in figure below. This reinforcement is provided on both top and bottom face of the slab.

Fig: Detailing of medium slab openings

3. Detailing of Slab openings of 450mm to 900mm

For slabs with openings more than 450mm and less 900mm, at least one half the quantity of main steel reinforcement intersected by the opening is provided parallel to the main reinforcement bars on each side of the opening extending a length of development length L_d beyond edges of the opening on both top and bottom slab face as shown in figure below. In addition to this, diagonal bars are provided on both top and bottom face of the slab as shown.

Fig: Detailing of large slab openings

4. Detailing of Larger Slab Openings

For larger slab opening larger than 900mm, it should be specifically designed and detailed. It is recommended to use beams below larger slab openings.