Clause 26.5 specifies minimum and maximum spacing limits for reinforcement. Minimum spacing ensures proper concrete compaction around bars. Maximum spacing limits crack widths for serviceability. Both horizontal and vertical spacing rules apply for bars in multiple layers.
Key Requirements
•Minimum horizontal spacing between parallel bars: max of (bar diameter, max aggregate size + 5 mm, 25 mm)
•Minimum vertical spacing between bars in layers: 15 mm or bar diameter, whichever is greater
•Maximum spacing of main tension reinforcement in slabs: min of (3d, 300 mm) — Clause 26.3.3(b)
•Maximum spacing of distribution bars in slabs: min of (5d, 450 mm)
•For beams: maximum spacing between side face bars (where depth > 750 mm): 300 mm — Clause 26.5.1.3
Reference Tables
Spacing Limits Summary (Clause 26.5)
Condition
Minimum
Maximum
Horizontal spacing (beams/slabs)
max(φ, agg+5, 25 mm)
—
Vertical spacing (layered bars)
max(15 mm, φ)
—
Main bars in slabs
—
min(3d, 300 mm)
Distribution bars in slabs
—
min(5d, 450 mm)
Side face reinforcement (depth > 750 mm)
—
300 mm
Practical Notes
✓For a typical 150 mm slab (d ≈ 125 mm): max main bar spacing = min(375, 300) = 300 mm; max distribution bar spacing = min(625, 450) = 450 mm.
✓When using bundled bars, treat the bundle diameter as equivalent diameter = φ × √n (where n is number of bars in bundle) for spacing checks.
✓For deep beams (depth > 750 mm), provide side face reinforcement at ≤ 300 mm spacing, area ≥ 0.1% of web area on each face.
Common Mistakes
⚠Spacing bars at exactly 300 mm in slabs without checking 3d — for thin slabs (d < 100 mm), the limit is 3d = 300 mm, but for d = 90 mm, it's 270 mm.
⚠Forgetting minimum spacing during congested beam-column joints — bars must still have enough gap for concrete to flow around them.
⚠Not providing side face reinforcement in beams deeper than 750 mm.