LAPPING ZONE AND LAPPING LENGTH OF SLAB , BEAM AND COLUMN

LAPPING ZONE AND LAPPING LENGTH OF SLAB , BEAM AND COLUMN FOR BUILDING DETAILING

As a civil engineer it very important to know about lapping zone and lapping length. Here we will discuss about lapping length and lapping zone of beam ,column and slabs.

Due to the restricted bar length, lapping of bars is needed in a member greater than 12 m in length or where the minimum bar length is more than 12 m in length.

Lap Longitude:- Bar length needed to safely pass tension. Overlapping Length or Lap Length is provided to preserve bar continuity and ensure a smooth transfer of the load from one bar to another. This depends on Concrete Standard, steel grade and dia grade. From the Restaurant.

LAPPING ZONE AND LAPPING LENGTH OF SLAB

HOW MUCH LAP LENGTH IS PROVIDED IN SLAB ?

In case of slab we use lap length 50dwhere ‘d’ is dia of bar.
one lap joint to another lap joint should be minimum 75 mm as show in figure.

LAPPING ZONE AND LAPPING LENGTH OF SLAB

IMPORTANT POINT SHOULD BE REMEMBER FOR SLAB LAP LENGTH:

The work of RCC slabs resembles beams if the slab is constructed in one way. Ideal for lap bars at least bending moment or at counter flexure stages.

Practically laps are supported from a bar support at the bottom of the slab, beyond L/5 to L/3 (L being the effective span). Generally, the top bars are low, so no laps are needed. The lapped bars however at no stage surpass one third of the total bars.

Bars are called staggered if at least the end-to – end distance b / w laps is (lap length +75 mm).

LAPPING ZONE AND LAPPING LENGTH OF BEAM

How Much Lap Length is Provided in Beam ?

24d for compression zone.
45d for tensile/tension zone.

LAPPING ZONE AND LAPPING LENGTH OF SLAB , BEAM

IMPORTANT POINT SHOULD BE REMEMBER FOR BEAM LAP LENGTH:

In top bars the lapping (24d) avoided L/3 gap from both ends. Mid span should be for top bar lapping.

At column junction or L/4 distance from column face, lapping (45d) in the bottom bars lap should be given but should not be in the mid span of beam.

Stirrups should be spaced close to the columns and should lose / normal at mid-span.

Alternatively, Bar lapping should be given.

LAPPING ZONE AND LAPPING LENGTH OF COLUMN

HOW MUCH LAP LENGTH IS PROVIDED IN COLUMN ?

The length of the overlap should be no less than 75 mm. In the tensile zone of building members lapping should be discouraged. Generally we take 24d – 40d in the case of column where ‘d ‘ is bar dia.

LAPPING ZONE AND LAPPING LENGTH OF COLUMN

IMPORTANT POINT SHOULD BE REMEMBER FOR COLUMN LAP LENGTH:

In the center of the column, lapping should be given because the bending moment at midpoint is zero so continue to lap at midpoint.

Alternatively, Bar lapping should be given. Lap should not be issued at the same time, as there may be buckling.

In the Lapping zone, lateral ties should be established spaced closely.

We can’t lap at the column / beam / slab join because of high tension. Lapping should not be provided from top and bottom of the slab at a distance of L/4.

Tension Lap Splice Lengths As Per ACI 318-24