Lap Length Calculator

The SkyCiv Lap Length Calculator is a free tool designed to help structural engineers determine development and lap lengths for reinforced concrete. The rebar lap length calculator supports all available rebar sizes and concrete strengths, whilst supporting factoring for reinforcement bundling, lightweight concrete and plain (round) bar reinforcement. All calculations are performed in accordance with AS 3600:2018, with a detailed calculation report generated upon completion.

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About the Lap Length Calculator

What is Reinforcement Development Length?

Development length is the minimum length of reinforcing bar that needs to be embedded into concrete for it to develop its full yield strength. If reinforcement is embedded less than its development length, it may de-bond from the concrete before being stressed to its full capacity upon loading. Reinforcement development lengths differ for tensile and compressive loading. Providing cogs, hooks and terminators at the ends of reinforcement can reduce its required development length.

What is Reinforcement Lap Length?

Rebar lap length is the minimum overlap required between two reinforcing bars to ensure full stress transfer between the bars. Reinforcement lengths in beams/slabs can often be limited due to fabrication and construction constraints, meaning lapped splices are required to achieve reinforcement continuity throughout the structural element. Lap length is generally proportional to the development length of the reinforcement in the splice connection. Reinforcement can be spliced by lapping, welding or mechanical couplers.

What factors affect Development and Lap Length?

Development length is predominantly governed by two factors:

  • Reinforcement Yield Force (kN): The force required to fully yield the reinforcing bar. This force is governed by reinforcement diameter (db) and material strength (fsy). Larger bars with higher strengths will generally require longer development lengths.
  • Concrete Strength (MPa): Higher concrete strengths allow for better transmission of stress into the reinforcing bar, reducing the required development length.

Factors such as reinforcement cover, transverse reinforcement, bundling and concrete density can also affect development length.

How to use the Reinforcement Lap Length Calculator?

The SkyCiv Reinforcement Lap Length Calculator is simple to use. Begin by entering the required inputs:

  • Concrete Grade (MPa)
  • Reinforcing Bar Diameter (mm)
  • Reinforcement Strength Grade (MPa)

Next, click the run button in the top right of the calculator to get your results:

  • Tension Development Length (Lsy.tb)
  • Compression Development Length (
  • Tension Lap Length (Lsy.t.lap)
  • Compression Lap Length (Lsy.c.lap)

Rebar Lap Length Calculator FAQs

All calculations are performed in accordance with AS 3600:2018 Concrete Structures. References to relevant sections of the Standard are included in the generated calculation report. Note, this calculator only supports metric units at this time.
Yes, this calculator supports all concrete grades (20-65MPa) and reinforcement strengths (250/500MPa) covered by AS 3600:2018 Section 13. The tool also has support for factoring due to lightweight concrete.
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