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Estimating Sheet

Calculation of overlapping length for RCC

Construction Software

The required length of the concrete section in RCC structures can't be maintained with a single reinforcement bar. Therefore, two bars must be overlapped to keep the required length.

This length overlapped with two bars in concrete sections is known as lap length or overlapping length and separate calculations are done for overlapping length for beams, columns and slab sections.

Measurement of Lap Length or Overlapping Length:

The lap length is measured for those concrete sections whose length remains in excess of 12m. Typically, 12m means the stock length that is rigid to allow smooth transportation to the site as well as handling.

1. Lap lengths for several splices - The lap splices are categorized as follow :

a. Contact Splices
b. Non-Contact Splices

Contact Splices: Under this type, the reinforcement bars remain in contact and wired collectively. They are classified as follow :

i. Trench Mesh Laps: The trench mesh lap is found in concrete reinforcement. The least length to be overlapped is 500mm. These overlap are created in T or L intersections at a width of the trench mesh.

Also Read: Guidelines for measuring steel reinforcement & its quantity in slab, beams, columns & footing

ii. Square Mesh Laps: The square mesh lap follows an overlapping length not below 225mm.

iii. Reinforcement Lap: Reinforcement lap follows a lapping length not below 500mm.

2. Lap length in Tension: The lap splice length in tension reinforcement is measured according to ACI 12.15. In a tension lap, the force is transmitted from the reinforcement bars to the concrete with the bond and in turn forces back to the reinforcement. As a result, a continuous line of reinforcement is created.

Under this circumstance, the lap splice demonstrates different interaction based on the concrete strength, grade of steel reinforcement, location, bar size ,and spacing. According to ACI 318, the tension lap splices are available in two classes Class A and Class B ( Table R12.5.2, ACI 318) for which the lap length should be as follows:

Class A Splice: Lap Length ls = 1.0 ld
Class B Splice: Lap Length ls = 1.3ld

Here, ld denotes development length, that is calculated according to ACI 12.2 ( excluding the modification factor).The least lap length is 12 inches.

3. Lap Length for Compression Bars: The lap length for compression lap splice is measured according to ACI 12.16.1 as follow :

ls = 0.0005fy (d) ; [ For fy less than or equal to 60,000psi]
ls = (0.0009fy – 24)d; [ For fy > 60,000 psi]

The least lap length for compression bars should remain 12inches. While reinforcement bars of varied sizes are combined as compression bars, the lap length should be greater than the following cases:

1. Compression splice length of the least diameter bar or
2. Compression development length of the largest bar

Calculation of overlapping length for RCC