Clause 40.4 covers the design of shear reinforcement (stirrups and bent-up bars) to carry the shear force exceeding the concrete shear capacity. Vertical stirrups are the most common form. The spacing of stirrups is computed from the excess shear (Vus = Vu − τc·b·d).
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Key Requirements
•Shear reinforcement capacity: Vus = 0.87 fy Asv d / sv (for vertical stirrups)
•Stirrup spacing sv shall not exceed: 0.75d or 300 mm, whichever is less
•Minimum shear reinforcement (even when τv ≤ τc): Asv ≥ 0.4 b sv / (0.87 fy)
•Bent-up bars: not more than 50% of total shear may be carried by bent-up bars
•Inclined stirrups (45°): Vus = 0.87 fy Asv d (sin α + cos α) / sv
Reference Tables
Maximum Stirrup Spacing for Minimum Shear Reinforcement
Stirrup
Fe415
Fe500
2L 8 mm (Asv = 100.5 mm²)
157 mm
189 mm
2L 10 mm (Asv = 157.1 mm²)
246 mm
296 mm
2L 12 mm (Asv = 226.2 mm²)
300 mm (max)
300 mm (max)
From: sv = 0.87 fy Asv / (0.4 b). For b = 230 mm.
Formulas
Vus = 0.87 fy Asv d / sv
Shear capacity of vertical stirrups
Vus = Shear resistance of stirrups (N)fy = Yield strength of stirrup steel (MPa)Asv = Total cross-sectional area of stirrup legs (mm²)d = Effective depth (mm)sv = Spacing of stirrups along the member (mm)
sv = 0.87 fy Asv d / Vus
Required stirrup spacing (rearranged for design)
sv = Required stirrup spacing (mm)Vus = Excess shear = Vu − τc × b × d (N)
Practical Notes
✓For most residential beams (230 × 450, d=410, M25, pt≈0.5%): τc ≈ 0.49 N/mm². Concrete carries Vc = 46 kN. Beyond this, 2L 8mm @ 150 c/c gives Vus = 0.87×500×100.5×410/150 = 120 kN. Total capacity = 166 kN — adequate for most spans up to 5 m.
✓IS 13920 (seismic detailing): stirrup spacing in the plastic hinge zone (2d from face of column) ≤ d/4 or 8φ of longitudinal bar or 100 mm, whichever is least.
✓Always provide at least 2-legged stirrups. 4-legged stirrups are needed for beams wider than 300 mm.
Common Mistakes
⚠Exceeding maximum stirrup spacing of 0.75d or 300 mm — for a 400 mm deep beam (d=360): max spacing = 0.75 × 360 = 270 mm, not 300 mm.
⚠Not providing minimum stirrups throughout — stirrups are required even in zones where τv < τc.
⚠Using Fe250 stirrup strength in calculations when Fe500 stirrups are actually provided — this is conservative but wastes steel.