Bond, Anchorage & Development Length Notes

Last reviewed 16 Sept 2026 · 7 min read

Bond

Bond is the grip between reinforcement and the surrounding concrete. It lets the tensile force in a bar be transferred to concrete so the two act together. Without bond, bars would slip and the beam would behave like unreinforced concrete.

Bond is developed by:

Adhesion — chemical gum between cement paste and steel.
Friction — due to shrinkage of concrete gripping the bar.
Mechanical interlock — ribs of deformed (HYSD/TMT) bars bearing on concrete. This is by far the most important for modern bars.

Type of bond	Where it acts
Flexural (local) bond	Along a beam where the bar force changes with bending moment; stress $\propto$ rate of change of moment (shear)
Anchorage (development) bond	At bar ends, cut-off points and laps, where the full bar force must be transferred over a length

IS 456:2000 designs primarily for anchorage bond through development length; adequate development length also takes care of local bond.

Design bond stress

Code ProvisionIS 456 — design bond stress τbd for plain bars in tension (N/mm²)

M20	M25	M30	M35	M40 and above
1.2	1.4	1.5	1.7	1.9

Deformed bars (IS 1786): increase these values by 60%.
Bars in compression: increase the tension values by 25%.

Development length

The development length $L_{d}$ is the embedment needed on each side of a section to develop the design stress in the bar.

Equating the bar force to bond resistance:

\frac{π ϕ ^{2}}{4} σ_{s} = π ϕ L_{d} τ_{b d} \Rightarrow L_{d} = \frac{ϕ σ _{s}}{4 τ _{b d}}

with $σ_{s} = 0.87 f_{y}$ at the limit state of collapse.

FormulaDevelopment length values (commonly used)

Bar and concrete	Tension	Compression
Fe 250 plain, M20	$\frac{217.5 ϕ}{4 \times 1.2} = 45.3 ϕ$	$36.3 ϕ$
Fe 415 deformed, M20	$\frac{361 ϕ}{4 \times 1.92} = 47.0 ϕ$	$37.6 ϕ$
Fe 415 deformed, M25	$40.3 ϕ$	$32.2 ϕ$
Fe 500 deformed, M20	$56.6 ϕ$	$45.3 ϕ$
Fe 500 deformed, M25	$48.5 ϕ$	$38.8 ϕ$

Bundled bars: $L_{d}$ of each bar is increased by 10% for two bars in contact, 20% for three and 33% for four.

Anchorage

Where the straight length available is short, bars are anchored with hooks and bends.

Anchorage value of a standard U-hook (180°): 16φ; of a 90° bend: 8φ — counted toward $L_{d}$ . The anchorage value of a bend is 4φ for each 45° of bend, up to 16φ.
Deformed bars in tension may be anchored with straight lengths or bends; hooks are generally used for plain bars.
Bars in compression: hooks and bends are not counted in anchorage (they are ineffective and may cause spalling); only the straight length counts.
Stirrups and links are anchored by a 135° or 180° hook around a longitudinal bar, or a 90° bend with sufficient extension.
Minimum radius of bends for bars: IS 456 specifies bend radii to avoid crushing the concrete inside the bend; bearing stresses inside bends must be checked when bars are heavily stressed.

Check at simple supports and points of inflexion

At a simple support (and at points of inflexion), the positive-moment tension bars must satisfy:

FormulaIS 456 — development length at supports and inflexion points

L_{d} \leq \frac{1.3 M _{1}}{V} + L_{0}

$M_{1}$ = moment of resistance of the section, assuming all bars at the section are stressed to $0.87 f_{y}$ .
$V$ = shear force at the section due to design loads.
$L_{0}$ = sum of the anchorage beyond the centre of the support and the equivalent anchorage value of any hook or bend; at a point of inflexion, $L_{0}$ = the greater of $d$ and $12 ϕ$ .
The factor 1.3 applies only where the reaction confines the bar ends with compression (e.g. a beam bearing on a wall or column); otherwise use 1.0.

At least one-third of the positive moment steel in simple members (one-fourth in continuous members) must extend along the same face into the support to a length of $L_{d} /3$ .

Downloaded from civilgyantests.com · Not for resale. Verify every code clause and date against the official source.

Bond, Anchorage & Development Length