Reinforcement placement in concrete beams and slabs
The beams and slabs are vital concrete structural members and the highest and lowest spacing reinforcement should be provided with adherence to the standard codes.
The lowest reinforcement spacing is provided on the basis of maximum size of aggregates with the purpose of placing and compressing the concrete in a perfect manner.
The highest reinforcement spacing is provided on the basis of depths of the beams and slabs to arrange sufficient support for bending moment and shear force in design.
Spacing of Reinforcement in Concrete Beams and Slabs
1. Lowest spacing among bars in tension
The lowest horizontal spacing among two parallel main bars should be diameter of larger bar or maximum size of coarse aggregate and 5 mm. However, when the needle vibrator is used to perform compaction, the spacing is again decreased to two-third of the nominal maximum size of the coarse aggregate.
The least vertical distance among two main bars should be :-
a. 15 mm,
b. Two-third of the nominal size of coarse aggregate, or
c. Maximum size of the bar or whichever is higher.
Maximum Spacing among Bars in Tension
Generally, these spacings are provided as follow :
For beams: these spacings are 300 mm, 180 mm and 150 mm for grades of main reinforcement of Fe 250, Fe 415 and Fe 500, correspondingly.
(i) The highest spacing among two parallel main reinforcing bars should be 3d or 300mm or either is less, and
(ii) The highest spacing among two secondary parallel bars should be 5dor 450 mm or either is less.
Lowest and Highest Reinforcement Necessary in Members
1. Lowest tensile steel is provided with the ratio (For Flanged Beams b=bw)
2. Highest Tensile Reinforcement in Beams should not be in excess of 0.04 bD.
3. Highest area of compression reinforcement should not be in excess of 0.04 bD.
4. Beam with depth surpassing 750 mm, side face reinforcement of 0.1% of web area should be arranged. This reinforcement should be allotted evenly on two faces at a distance not surpassing 300 or web thickness or either is less.