Standard spacing requirements in different structural members
The lowest and highest spacing reinforcement in various concrete structural members like beams and slabs are settled according to standard codes. The least reinforcement spacing is dependent on maximum size of aggregates, in order that the concrete is arranged and condensed in a perfect manner. The highest reinforcement spacing is dependent on the depths of the beams and slabs to arrange enough support for bending moment and shear force in design.
Spacing of Reinforcement in Concrete Beams and Slabs
1. Least Spacing among Bars in Tension: The least horizontal spacing among two parallel main bars should be the diameter of larger bar or maximum size of coarse aggregate plus 5 mm. However, where compaction is performed with needle vibrator, the spacing is again minimized to two-third of the nominal maximum size of the coarse aggregate.
The least vertical distance among two main bars should be as follow :-
Two-third of the nominal size of coarse aggregate, or
Maximum size of the bar or whichever is higher.
2. Highest Spacing among Bars in Tension
Usually, these spacing are provided as follow :
For beams, these spacing should be 300 mm, 180 mm and 150 mm for grades of main reinforcement of Fe 250, Fe 415 and Fe 500, respectively.
(i) The highest spacing among two parallel main reinforcing bars should remain 3d or 300mm or whichever is lower.
(ii) The maximum spacing among two secondary parallel bars should remain 5dor 450 mm or whichever is lower.
3. Lowest and Highest Reinforcement Requirement in Members
a. Minimum tensile steel is provided with the ratio (For Flanged Beams b=bw)
b. Highest Tensile Reinforcement in Beams should not surpass 0.04 bD.
c. Highest area of compression reinforcement should not surpass 0.04 bD.
d. Beam with depth over 750 mm, side face reinforcement of 0.1% of web area should be arranged.
This reinforcement should be allocated uniformly on two faces at a gaping not surpassing 300 or web thickness or whichever is less.