How does one calculate bend length and hook length of steel bars in order to make BBS?
Length of Hook’s in Stirrups:
We generally consider length of hook = 10 D (for bars having diameter greater than or equals to 8mm)
Where D → Diameter of stirrup
Is code recommends, Minimum hook length = 75 mm
fig:- Hook in stirrup
Bend Length
For 45 degree bend, length of reinforced bar increase by 1d
For 90 degree bend, length reinforced bar increase by 2d
For 135 degree bend, length reinforced bar increase by 3d
Example:-
Q:- Calculate the cutting length of the stirrups given in fig. Clear cover of beam is 25 mm
fig : Cross section of beam[/caption]
Ans:-
Given data:
Clear cover = 25 mm
Depth of beam = 400 mm
Width of beam = 230 mm
Diameter of stirrup =8 mm
Cutting length of stirrup = 2a+2b + (2 x Hook length) - Bend deduction
Where,
a= Width of beam - (2 x clear cover) - ( 2 x Half of diameter of bar)
b= Depth of beam - (2 x clear cover) - ( 2 x Half of diameter of bar)
Therefore,
a= 230 - (2 x 25) - (2 x 4) = 172 mm
b= 400 - (2 x 25) - (2 x 4) = 342 mm
Length of hook (Development length) = 10 d = 10x8 = 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 (2x8) = 3x16 = 48 mm
135 degree bent --> 2 no's
For 135 degree bend, length reinforced bar increase by 3d
i.e., Bend length = 2 x (3x8) = 2 x 24 = 48 mm
∴ Cutting length of stirrup = (2x172) + (2x342) + (2x80) - (48+48) = 1428 - 96 = 1092 mm
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