Ans:-

Given data:

Clear cover = 25 mm

Depth of beam = 450 mm

Width of beam = 300 mm

The diameter of stirrup =8 mm

Cutting length of stirrup = 2a+2b + (2 x Hook length) – Bend deduction

Where,

a= Width of the beam – (2 x clear cover) – ( 2 x Half of the diameter of the bar)

b= Depth of beam – (2 x clear cover) – ( 2 x Half of the diameter of the bar)

 

Therefore,

a= 300 – (2 x 25) – (2 x 4) = 242 mm

b= 450 – (2 x 25) – (2 x 4) = 392 mm

Length of hook (Development length) = 10 d = 10×8 = 80 mm

Bend deductions:

90-degree bent –> 3 no’s

For 90 degree bend, length reinforced bar increase by 2 d

i.e., Bend length = 3 x (2×8) = 3×16 = 48 mm

135-degree bent –> 2 no’s

For 135 degree bend, length reinforced bar increase by  3d

i.e., Bend length = 2 x (3×8) = 2 x 24 = 48 mm

∴ Cutting length of stirrup (2×242) + (2×392) + (2×80) – (48+48) = 1428 – 96 = 1332 mm

Why hook is provided in stirrups

The hook is provided in stirrups for the following reasons:

1- To prevent from buckling of the column.

2- The main requirement for safety against bond failure is to provide a sufficient extension of the length of the bar beyond the point where the steel is required to develop its yield stress and this length must be at least equal to its development length. However, if the actual available length is inadequate for full development, special anchorages must be provided, such as cogs or hooks or mechanical endplates.

3- Hooks are provided to resist seismic movement.

4- To prevent concrete from splitting outward.

5- It prevents slippage of steel from the concrete.

6- To Keep longitudinal steel bars in position and hold steel tightly.

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