PNRC 41 - Fixing of Reinforcement for Concrete Works [for study only]
Table of Contents
Introduction
This article would introduce the content of PNRC 41 – “Fixing of Reinforcement for Concrete Works”.
Spacers and Chairs for Steel Reinforcement
Spacers and chairs should be placed at a maximum spacing of 1.5 m.
In the case of 20 mm diameter or smaller bars, the spacing of chairs and spacers should be suitably reduced to avoid sagging.
Spacers within Columns and Walls (BS 7973-2)
Some specifications regulate the workmanship of spacers by making reference to “BS 7973-2: Spacers and chairs for steel reinforcement and their specification”, such as “Standard Specification by Arup” (as shown below).
BS 7973-2: Spacers and chairs within walls
Taking spacers and chairs within walls as an example for BS 7973-2-8.5,
- For spacers (i.e. to maintain face cover), in two directions at right angles, at centers not exceeding 50d or 500 mm, whichever is the greater, and staggered (as clouded in blue below).
- For chairs (i.e. to maintain the position of rebar), in walls up to 400 mm thick shall be separated by rows of continuous chairs (preferably vertically) at centers not exceeding 1000 mm (as clouded in red below).
Material for spacers
Spacers for reinforcement should be (1) concrete or (2) proprietary plastic. The strength and durability of spacers should not be less than that of the surrounding concrete.
Avoidance of Displacement of Reinforcement
- Sufficient number of intersecting and lapping bars should be tied by tying wire.
- Access (e.g. persons walking) should be obtained by using planks and ladders which are independently supported and well clear of the completed reinforcement.
Laps and Joints
Laps and joints in reinforcement should be located only at the specified positions.
Examples could refer to “Code of Practice for Structural Use of Concrete 2013 (2020 Edition)” as shown below:
Lap
For ductility requirements (i.e. wind frame elements), no portion of the splice by lap shall be located within one effective depth from the column/wall face.
The centre of the lap or coupler must be within the middle half of the storey height of the column (as shown below) unless plastic hinges cannot develop in the column (by comparing moment capacity for column to moment capacity for beams on both sides of the beam-column joints.
Coupler
For type 1 mechanical couplers, no portion of the splice shall be located within one effective depth from the column/wall face.
For type 1 mechanical couplers in a column, the centre of the coupler must be within the middle half of the storey height of the unless it can be shown that plastic hinges cannot develop in the column. Besides, type 1 mechanical couplers should be staggered in at least 2 layers at not less than 900 mm apart (as shown below).
Type 2 mechanical couplers should be staggered in at least 2 layers (S.F.L + 300mm + 300mm) as shown below.
Testing, Supervision and Inspection
Bar reinforcement and fabric reinforcement from each batch should not be fixed until testing of the batch has been completed. The details for rebar test refers to PNRC 33 – Testing of Reinforcement for Concrete
The registered contractor should provide continuous supervision, to ensure that:
The fixing of reinforcement is carried out in accordance with the approved plans.
The recommendations given in this PNRC 41 are followed.
No displacement of reinforcement takes place during placement and compaction of concrete.
The registered contractor should inform the AP/RSE to inspect all reinforcement after fixing and well in advance of concreting to allow for any necessary rectification. ← Basis for Rebar Fixing Inspection
THIS DOCUMENT IS FOR REFERENCE PURPOSES ONLY.