beam lap zone | lap zone in beam |lap zone in continuous beam

beam lap zone | lap zone in beam |lap zone in a continuous beam

Beam lap Zone

If the span of a structural member needs to be increased beyond the standard (provided length) which is generally 40 feet or 12meter then we must increase the length of bars by adding another steel. The most important thing, our IS CODE does not allow the bars directly from end to end to avoid the risk of steel sliding out of concrete. That is the reason why we overlap the bars at certain points to allow an easy transfer of loads from one bar to the next.

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Before confirming to the lapping zone of beams, we need to know the points or places where a member is subjected to a maximum bending moment, or simply, we need to identify the flexural tension zones of a beam.

For example, let’s consider a continuous beam that is subjected to a uniformly distributed load.

Reinforcement lapping zone in Beams

Due to this loading(udl), the beam will tend to bend in a way that the maximum bending moments will be generated at the centre of the spans. There will be positive moments at the centre of the spans & negative moments at support.

Due to the maximum bending moment, the top fiber of the beam at each end & the bottom fiber in the mid-span will experience maximum tension. Hence, they can be called flexural tension zones of the beam &we can’t overlap the bars in tension zones because the reinforcement bars tend to pull out of the concrete due to maximum stress.

For bottom bars, we cannot overlap the bars at the mid-span of the beam due to maximum flexural tension in the bottom fiber of the beam. On the other hand, the top bars can be overlapped in the mid-span of the beam due to minimum tension in the top fiber of the mid-span.

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If we divide the span into 3 equal parts, the overlapping of top bars should be done in the intermediate zones & each bar should be overlapped at alternative levels within the lapping zones.

The bottom bars should be overlapped at column junctions up to a distance of L/4 from each end & each bar should be overlapped at alternative levels within the lapping zones.