Diff Between Development length and Overlapping length

Diff Between development Length and Lapping lenth

Development length (Ld)

“ The embeded length in concrete is called development length”

The minimum length of steel bars necessary on either side of section to develope bond is called as development length "

formula for finding Ld from IS Code

As per IS 456-2000
Clause:26.2.1
For LSM
Development length= (0.87 fy Ø)/(4τbd)
Ø= nominal diameter of the bar, fy : grade of steel
τbd = design bond stress given in 2.6.2.1.1.

Note – For Hysd steel bars increase values by 60%

How Much Ld provided

beam and slab – 48d

Column – 60d

Overlapping length

“The lap of bar needed ti transfer stresses to onther bars

ie means the available size of steel bars in market is 12 meter , if we have maximum span in beam , column and slab etc then we have to use two bars . That is required suffiecient length for transfering of stresses from one bar to onther is called lapping length

lapping length

beams and slab- 60d

columns – 45d

Why Bent Up Bars are provided and Cutting Length of bent up bars

Why Bent Up Bars are Provided in Beam and Slab

“ It is economical of material .normally for fixed beams and slab postive moments (Sagging) momments are mid span and Negateive moments (Hogging) at the Supports

so Bottom Steel is required at mid span and top steel resist negative moment at support "

• To resist negative bending momemt ie Hoggin
• To resist shear forc which is greater at Supports
• To reduce risk of brittle failure of slab and column connection

How much Bent Up Provided

 

1- Continuous slab ­ L/5

2- For End Support ­L/7

Cutting Length of Bent up Bars

• Extra length = d/sin45-d= 0.42d for one bent up

• Extra Length of 2 bent up = 2x0.42d = 0.84d

• d= D – (top+bottom cover)