Bond and anchorage

Bond 

• it is a resistance which avoids the relative movement of concrete & steel 

b/w structural member.

• Bond stress is the resistance offered by steel & concrete to resist relative 

movement b/w them.

• Bond b/w steel & concreate depends upon 3 parameters

i). adhesive Resistance

ii). frictional resistance

iii). Mechanical resistance

• Frictional Resistance is used to resist external Resistance by concrete.

• ➔ shrinkage strain in concrete is 0.0003

• Mechanical Resistance depends upon grade of steel.

• in HYSD bars, mechanical resistance is of prime importance due to a thread 

like formation over bar. this formation increases adhesive resistance also.

Also read Types of shear reinforcement bars

Development length

• Development length is the min length of bar req. to resist slippage b/w concrete 

& steel.

Development length is based upon local bond stress.

When max shear force is used to calculate bond stress, the Stress Is known as local 

bond stress.

• Development length depends upon grade of steel & bond stress.

• Bond stress depends upon grade of concrete

حbd ➔ 1.6 ح db ➔

 Ld =( 0.87fy∅/6.4حbd)

 if bars are used in compression, then bond stress is increased by 25%

حbd → 1.25 db ➔ 

Ld=0.87fy∅/5حbd

Check for development length

Check for development length

Anchorage length

• It is the length of bar which is provided to ensure the safety against frictional 

resistance.

• Anchorage length in any case should not be greater than if seems diameter of 

bars. 

1). Lo > 16 ∅

2). straight bars Lo > d

                          = 12∅

3). for every 45°  bend➔ 4∅

4). 90° bend ➔ 8 ∅

5). 135° bend ➔ 12 ∅

Stress is known as Local bond stress

Compressive force, C = 𝜏bd x 𝜋∅𝐿𝑑

Tensile force, T = 0.87fy AsL

                             = 0.87 fy ∅2

• Development Length depends upon grade of steel & bond stress.

• Bond stress depends upon grade of concrete.

If HySD bars are used, then bond stress is increased by 60%.

• If bar diameter is more than 36 mm, lap splices are not provided, bars are 

joined by welding.

Curtailment of bars

• Curtailment of bars represent the cutting of bars along the span of beam when 

the req. of moment decreases.

• This curtailment can be done for negative steel as well as positive steel.

• The bars are curtailed by 30& at distances of 0.12L.

Lap length in Tension = Ld or 30∅ whichever is more

Lap length in compression = Ld or 24∅ whichever is more

vi) 180°bend → 16 ∅

Lap splices

• It is the overlapping of bar that have ot be provided to increase the length of 

bar.

• If diameter of bar is up to 36mm, lap splices are provide with max. value of 

24∅.

Ld calculated <( 𝑀𝑚𝑎𝑥/𝑉𝑚𝑎𝑥)+Lo

If support width is considered

Ld calculated < (1.3𝑀𝑚𝑎𝑥/𝑉𝑚𝑎𝑥)+ Lo

Anchorage Length(Lo)

• It is length of bar which is provided to ensure the safety against frictional 

resistance.

• Anchorage Length in any case should not be greater than 16 times diameter of 

bars.

i) Lo > 16 ∅

ii) straight bars

iii) For every 450 bend → 4∅

iv) 90°bend → 8∅

v) 135° → 12∅

Tbd → 1.6 Tbd → Ld = (0.87fy∅/6.4𝜏bd)

Check for Development Length

Mmax = Max. B.M. on beam

Vmax = Max. S.F. on beam

Lo= Anchorage length

Ld(calculated) = 0.87fy∅/4𝜏bd

If support width are not considered.