Answer Posted / shamshad

Cutting Length of Bent Up Bars

So you have given reinforcement detailing of a slab.

Now you have to give instructions to the bar benders about cutting length of the steel bar according to the slab dimensions.

If it is a small construction, you can hand over the detailing to the bar benders they will take care of cutting length. However, that must not be perfect. They actually don’t give importance to the bends and cranks.

They may give some extra inches to the bars for the bends. But it’s not the correct way.

Let’s do it in a right way…

We are not going to explain the whole reinforcement detailing. [BBS Shape Codes]

We are taking the below example of single reinforcement – bent up bar to explain

Given

Beam Cross Section

Diameter of the Bar = 12 mm

Clear Cover = 25 mm

Clear Span (i.e “L”) = 6000 (Length of the slab)

Slab Thickness = 150 mm

Ld = 40d (Development Length). We know the difference between lap length and development length.

Calculation
Therefore,

Bent up Bar cross section

Cutting Length = Clear Span of Slab + (2 X Developement Length) +(2 x inclined length) – (45° bend x 4) – (90° bend x 2)

Cutting Length = Clear Span of Slab + (2 X Ld) +(2 x 0.42D) – (1d x 4) – (2d x 2) [BBS Shape Codes]

In the above formula, we have all the value, (except D)

Ld – Development Length which is equal to 40d

d – Diameter of Bar

So D = height of the bend bar (refer the image)

“D” = Slab Thickness – (2 x clear cover) – (diameter of bar)

= 150 – (2 x 25) – 12 = 88 mm

“D” = 88 mm

Now we know the “D” value which is the clear height of the bar (refer the image).

In order to find the inclined bar length using (Trignometry Function)

Inclined length = d/(sin 45°) – d / (tan 45°) = (d/0.7071) – (d/1)= (1d – 0.7071d)/0.7071= 0.42 D

we are providing four 45°bends at inner side (1,2,3 & 4) and two 90° bends ( a,b ).

45° = 1d ; 90° = 2d

Coming back to the formula,

Cutting Length = Clear Span of Slab + (2 X Ld) +(2 x 0.42D) – (1d x 4) – (2d x 2)

= 6000 mm + ( 2 x 40 x 12) + (2 x 0.42 x 88) – (1x12x4) – (2x12x2)

Cutting Length = 6938 mm or 6.94 m

So far the above dimensions, you need to cut the main bars in 6.94 m length.

Hope this helps. Happy Learning 🙂

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