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The placement of reinforcement in concrete members should conform to the applicable code and design requirements. It should also be ensured that concreting and consolidation processes of concrete are carried out properly.
Site engineers should closely monitor the installation of steel bars in order to maintain the designated spacing between steel bars, make room for concrete placement in congested members, and ensure the provision of concrete cover. The concrete cover protects steel bars from fire, aggressive environment, and buckling under the particular condition of compressive loads.
Practical Tips for Placement of Reinforcements in Concrete Members
- The site engineer should examine clearance at stirrups and column ties that protrude beyond other reinforcement.
- A clear cover between the top of the slab and the top of reinforcements must be maintained, especially if exposed to an aggressive environment as in the bridge deck slab.
- In the case of double mat reinforcement, it is advised to align steel bars vertically above each other in horizontal directions to facilitate concrete pouring and consolidation.
- Provide openings in the top mat reinforcement to place fresh concrete easily and prevent scattering and concrete segregation.
- In case of extremely congested reinforcement, create an opening by moving congested steel bars to each side to make way for concrete placement. Move the steel bars to the previous position after concrete pouring is completed. Sometimes, the displaced bars can be left at their place if the designer approves them.
- The nominal coarse aggregate size in the concrete mixture should not be greater than three-quarters of the spacing between bars to ensure the flow of concrete through steel bars and avoid honeycombing.
- The head of vibrators should fit between steel bars to consolidate concrete adequately. If a small vibrator head is used, reduce the spacing between vibration points and increase vibration time. All vibrators should be functional and prevent concrete placement unless spare vibrators are available.
- Stagger bar splices to ease the concrete placement.
- Ensure that the splice of column ties is staggered around the corners of the column. It is not recommended to place splice of column ties above each other.
- When splices are welded, make sure that the weld is of the required size and length. The bars should not be burned, or their cross-section should not be reduced due to welding.
- The use of tack welding is prohibited because it weakens the bars at the tack location. If contract documents allow tack welding, it should be done by professionals. It is recommended to carry out weld tests if many welds are made.
- It is common to use splicing sleeves for large bars.
- The mechanical splices should be approved by the designer otherwise it is not permitted to use.
- Anchor steel bars, whenever required, by bending it around another bar, by extending it to the point of zero stress, or by bending it to 90 degrees or semicircular hook of specified minimum radius.
Steel bars are commonly spaced as specified in the design. The spacing should not prevent the flow of fresh concrete around rebars.
Putting too much steel bar is uneconomical and may prevent the smooth flow of fresh concrete around the steel bar. Moreover, most concrete elements do not benefit from the full strength of high reinforcement since concrete could fail before the full potential of steel bars are used.