All about civil construction knowledge- PARAM VISIONS

Where to provide lapping in beam reinforcement?/ Basic rules for providing lap splice in a beam reinforcement.

 The lapping zone of top & bottom reinforcement in beams are different. Let us now go through the lapping rule for the top & bottom bars of a beam separately.

1. Top bar:

Given:

L1    👉 Clear span between columns 1 & 2.

L1/3 👉  One-third zone of the clear span L1.

L2    👉  Clear span between columns 2 & 3.

L2/3 👉  One-third zone of the clear span L2.


Rule 1:

The lapping zone for the top bars should be at the mid- L1/3 or L2/3 part of the beams.

Reason:

 The top bars fall under the compression zone of the beam. For the compression zone, the mid-1/3 span of the beam is said to be a safe zone for lapping. The negative moment in this section are low & hence there is a minimal chance of failure in this area.


Rule 2:

Not more than 50% of the top beam bars are lapped in the same zone of any clear span. 



As you can view in the above drawing, the beam has 2 reinforcement bars at the top. Top bar-1 should be lapped in the mid- L1/3 part of the clear span L1. Alternately, top bar-2 should be lapped in the mid-L2/3 part of the clear span L2. If you observe the above drawing, you will understand the concept clearly.

Reason: 

Providing lapping in the alternate zone of the beam helps in the safe transfer of the load & greatly reduces the chances of failure.


2. Bottom bar:


Given:

L1     👉  Clear span between columns 1 & 2.

L1/8 👉  One-eighth zone of the clear span L1.

L2    👉  Clear span between columns 2 & 3.

L2/8 👉  One-eighth zone of the clear span L2.


Rule 3:

The lapping zone for the bottom bars should be at the columns plus the end- L1/8 or L2/8 part of the beams.

Reason:

 The bottom bars fall under the tension zone of the beam. For the tension zone, the end-1/8th span of the beam near the column junction is said to be a safe zone for lapping. The positive moment in this section are less & hence there is a minimal chance of failure in this area.


Rule 4:

Not more than 50% of the bottom beam bars are lapped in the same zone plus columns of any clear span. 




As you can view in the above drawing, the beam has 2 reinforcement bars at the bottom. Bottom bar-1 should be lapped in the zone of [end- L1/8 + column 2 + end L2/8.]

Alternately, bottom bar-2 should be lapped in the zone of [end- L2/8 + column 3 + end L3/8.]. If you observe the above drawing, you will understand the concept clearly.

Reason: 

Providing lapping in the alternate zone of the beam ( not above 50%) helps in the safe transfer of the load & greatly reduces the chances of failure.

Thank you for going through this article. Have a good day😄.


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