3.1 Concrete and its reinforcement

Also see:

5.2

3.1.10 Installation of reinforcement

Reinforcement shall be installed in accordance with the design. Issues to take into account include:

  1. shape, placing and condition of reinforcement bars
  2. lapping bars and mesh
  3. support for reinforcement.

Shape, placing and condition of reinforcement bars#

Main reinforcing barsShould be parallel to the span, or as detailed in the design
Slab reinforcementShould be located near the bottom of the slab, with the main reinforcing bars placed first and the secondary bars on top
BeamsShould have the main reinforcing bars placed inside the links

Reinforcement should be:

  • bent using appropriate equipment and placed in accordance with the design
  • clean and free from loose rust and contaminants, especially shutter-releasing agents and oil.

Lapping bars and mesh#

Reinforcing bars or mesh should be lapped according to type and size as indicated by the designer to ensure that loads are fully transferred across the lap. Any additional laps require the designer’s approval.

Support for reinforcement#

Spacers should be either concrete blocks (no more than 50 x 50mm) or ready-made of steel or plastic. Supports should be placed no more than one metre apart, or closer where necessary.

Spacers for parallel bars should be staggered to avoid creating a plane of weakness in the concrete. Supports for top steel should be chairs, or other proprietary products.

Punching shear reinforcement#

Punching shear occurs when a slab is subjected to concentrated forces, for example where a column is offset from a supporting column or columns below and loads must be transferred by the slab.

Design for punching is covered in BS EN 1992-1-1. Where concrete stresses are exceeded, additional reinforcement is locally required. This will either be within the top or bottom (or both) layers of the slab reinforcement and/or be by including shear links joining these layers or additional lacer bars at regular centres around several spaced perimeters about the head or base of columns.

The additional reinforcement will typically be loose bars scheduled to BS 8666 that suit the structural design, with their location, spacing and cover requirements identified on engineers reinforcement detailing drawings. Bars will typically be either straight when included in the top and/or bottom layers, or ‘bob-and-hook’ or ‘U-bars’ as shear links.

However, there are several proprietary solutions for punching shear reinforcement, and these are commonly used in flat slabs in medium and high-rise residential buildings. These include stud rail systems, shear ladders and structural steel shear heads, amongst others. These may often be spaced at centres relaxed compared to those required for traditional shear links.

Such systems should be:

  • independently assessed, in accordance with Technical Requirement R3
  • assessed according to the intended use
  • used strictly in accordance with the manufacturers recommendations and the independent assessment
  • fully detailed and co-ordinated on engineers reinforcement detailing drawings.

Last updated: 2nd January 2024

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