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Development length of bars in tension and compression

Development length of deformed bars from the design bond stress, in tension and in compression. Reference: IS 456:2000 Cl. 26.2.1.

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# Data
phi := 20 mm
f_y := 415 MPa
f_ck := 25 MPa
tau_bd := interp(f_ck/(1 MPa), [20, 25, 30, 35, 40], [1.2, 1.4, 1.5, 1.7, 1.9])*1 MPa =
# Deformed bars: the bond stress is 60% higher; in compression a further 25% higher.

# Tension
tau_bd.t := 1.6*tau_bd =
L_d.t := phi*0.87*f_y/(4*tau_bd.t) = mm
L_d.t/phi =

# Compression
tau_bd.c := 1.25*tau_bd.t =
L_d.c := phi*0.87*f_y/(4*tau_bd.c) = mm

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