Answered What is the basic difference between lap length and development length?

Dnyan Deshmukh

Staff member
As you know the bars comes in specific length of 12 meters or any other length as per your country manufacturing standards.
Also using such high length bar is not feasible, because supporting such bar to that length cost huge and not practical when we place them vertically.

So by looking at feasibility of use we cut them to as practical as possible lengths and to continue the work we need to lap the new bar to old bar.

The lap in bar ensure the transfer of load from bar to bar (It should be provided as per instructions of Structural consultant, mostly it is written in the General notes of drawing and many prefer to specify single lap length in terms of bar diameter. If 2 lap length specified i.e. - in tension and in compression, site engineers with less knowledge may do mistake and cause a lot of rework, so consultant now a days prefer to provide single lap length number to avoid misunderstanding and reworks).

To transfer the stresses to concrete at fixed end i.e. in columns we do provide the development length or anchorage length to ensure load transfer.

When we provide the lap to bar, both bar should be in contact with each other.

When we provide development length or anchorage, it must go inside of the column reinforcement to ensure no failure due to getting out of reinforcement anchor from structural element in lateral movements.

As you know, the column sizes are reduce to achieve no offset in beam and column face, this aspect of anchorage is overlook and in most of the places fitter use to tie beam bar which comes on periphery of building from outside of the column reinforcement bars. If you had not observed it, i insist you all to do check reinforcement of beam specially at periphery of building.

The outer bar with anchorage / development length must go through inside of column rebar.
If not done, is situation of earth quakes due to lateral movement those bars which are simply placed in cover zone will come out of it and structure will fail.

Good Civil Engineer Always do check periphery beams for the above point.
 

Sanjay Borge

Apprentice
Development length Ld= 0.87Fy*dia of bar/4*design bond stress
the value of design bond stress is given in cl.no.26.2.1.1 of IS 456:2000 Page no 42 &43
 
I might be able to simplify Mr. Deshmukh's thourough discussion:

Lap Length is simply the overlapping of rebar to provide a continuous length made out of multiple bars
Development length is a structural design criteria as Mr. Deshmukh has described dealing with the tensile capacity of a reinforced concrete element

Think of it this way: A contractor will need to know the lap lengths during construction, but, he will not care about the development length since those "numbers" will be generated by the engineer in the design details.
 
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As you know the bars comes in specific length of 12 meters or any other length as per your country manufacturing standards.
Also using such high length bar is not feasible, because supporting such bar to that length cost huge and not practical when we place them vertically.

So by looking at feasibility of use we cut them to as practical as possible lengths and to continue the work we need to lap the new bar to old bar.

The lap in bar ensure the transfer of load from bar to bar (It should be provided as per instructions of Structural consultant, mostly it is written in the General notes of drawing and many prefer to specify single lap length in terms of bar diameter. If 2 lap length specified i.e. - in tension and in compression, site engineers with less knowledge may do mistake and cause a lot of rework, so consultant now a days prefer to provide single lap length number to avoid misunderstanding and reworks).

To transfer the stresses to concrete at fixed end i.e. in columns we do provide the development length or anchorage length to ensure load transfer.

When we provide the lap to bar, both bar should be in contact with each other.

When we provide development length or anchorage, it must go inside of the column reinforcement to ensure no failure due to getting out of reinforcement anchor from structural element in lateral movements.

As you know, the column sizes are reduce to achieve no offset in beam and column face, this aspect of anchorage is overlook and in most of the places fitter use to tie beam bar which comes on periphery of building from outside of the column reinforcement bars. If you had not observed it, i insist you all to do check reinforcement of beam specially at periphery of building.

The outer bar with anchorage / development length must go through inside of column rebar.
If not done, is situation of earth quakes due to lateral movement those bars which are simply placed in cover zone will come out of it and structure will fail.

Good Civil Engineer Always do check periphery beams for the above point.
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