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Minimum mandrel diameter for bent bars

Mandrel diameter to avoid damage to the bar, and the diameter needed to avoid failure of the concrete inside the bend. Reference: EN 1992-1-1 8.3.

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Minimum mandrel diameter for bent bars: worked example sheet in Equation Pad with typeset equations and results.

Example only. This sheet shows one way to set out the check. It is not endorsed by the bodies that publish the design codes and does not reproduce them. Check every clause, value and assumption against your own copy of the current edition of Eurocode 2 and its national annex before you use it, and have the result checked by a competent person. See the disclaimer.

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# Inputs
phi := 20 mm
F_bt := 120 kN
a_b := 60 mm
f_ck := 30 MPa
gamma_c := 1.5
# a_b is half the centre-to-centre spacing of the bars (or cover plus phi/2) perpendicular to the plane of the bend.

# Diameters
phi_m1 := phi <= 16 mm ? 4*phi : 7*phi =
f_cd := f_ck/gamma_c =
phi_m2 := F_bt*(1/a_b + 1/(2*phi))/f_cd = mm
phi_m := max(phi_m1, phi_m2) =

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More Eurocode 2 sheets on detailing

The same topic in IS 456