The minimum and maximum spacing reinforcement in concrete structural members such as beams and slabs are required as per standard codes. The minimum reinforcement spacing is based on maximum size of aggregates, so that concrete can be placed and compacted properly. The maximum reinforcement spacing based on depths of the beams and slabs to provide adequate support for bending moment and shear force in design.
Spacing of Reinforcement in Concrete Beams and Slabs
1. Minimum Spacing between Bars in Tension
The minimum horizontal spacing between two parallel main bars shall be diameter of larger bar or maximum size of coarse aggregate plus 5 mm. However, where compaction is done by needle vibrator, the spacing may be further reduced to two-third of the nominal maximum size of the coarse aggregate.
The minimum vertical distance between two main bars shall be
- 15 mm,
- Two-third of the nominal size of coarse aggregate, or
- Maximum size of the bar or whichever is greater.
2. Maximum Spacing between Bars in Tension
Normally these spacing will be as mentioned below :
- For beams, these distances are 300 mm, 180 mm and 150 mm for grades of main reinforcement of Fe 250, Fe 415 and Fe 500, respectively.
- For slabs
- (i) The maximum spacing between two parallel main reinforcing bars shall be 3dor 300mm or whichever is less, and
- (ii) The maximum spacing between two secondary parallel bars shall be 5dor 450 mm or whichever is less.
Fig: Spacing of reinforcement in beams
3. Minimum and Maximum Reinforcement Requirement in Members
- Minimum tensile steel is given by the ratio (For Flanged Beams b=bw)
- Maximum Tensile Reinforcement in Beams shall not exceed 0.04 bD.
- Maximum area of compression reinforcement shall not exceed 0.04 bD.
- (d) Beam having depth exceeding 750 mm, side face reinforcement of 0.1% of webarea shall be provided. This reinforcement shall be equally distributed on two faces at a spacing not exceeding 300 or web thickness or whichever is less.
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