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AS 3600:2018 (Amdt 2)Australia

Concrete Development Length

Australian structural engineers calculating tension and compression development lengths for reinforcement to AS 3600:2018 (Amdt 2). Handles hooked and straight bars with all standard modification factors applied automatically, and code references shown on every output.

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What it calculates

Calculate tension and compression development lengths for reinforcement to AS 3600:2018 (Amdt 2), with code references on every output. Handles hooked and straight bars, and applies the standard's modification factors automatically.

Code standards

  • AS 3600:2018 (Amdt 2)

How it calculates

The Concrete Development Length calculator computes tension and compression development lengths for reinforcing bars to AS 3600:2018 (Amendment 2), Section 13. It calculates both basic development lengths and refined development lengths, accounting for bar geometry, transverse reinforcement, cover, and stress conditions.

Basic development length in tension (AS 3600:2018, Cl. 13.1.2.2)

The basic tensile development length L_sy,tb is the minimum length required for a straight bar to develop yield strength, assuming minimum cover and transverse reinforcement:

L_sy,tb = k_1 × k_3 × f_sy × d_b / (k_2 × sqrt(f'c))

Where:

  • k_1 - bar position factor (1.3 for top bars with more than 300mm concrete below, 1.0 otherwise)
  • k_2 - concrete density modification factor
  • k_3 - bar size factor: (132 - d_b) / 100

Yield strength is limited to f'c ≤ 65 MPa. Bundled bars in tension are not covered.

Refined development length in tension (AS 3600:2018, Cl. 13.1.2.3)

The refined development length L_sy,t applies modification factors for transverse confinement and transverse compression:

L_sy,t = k_rdl × L_sy,tb

Where k_rdl combines factors k_4 (transverse confinement using the weighted average effectiveness factor lambda) and k_5 (transverse compression pressure factor). The transverse confinement factor lambda = (A_tr × n_f - 0.25 × d_b) / d_b accounts for the number and area of fitment legs.

For bars that do not need to reach yield, a refined development length for unyielding bars L_st = max(sigma_st / f_sy × L_sy,t, 12 × d_b) is also reported.

Development length in compression (AS 3600:2018, Cl. 13.1.5.3)

Basic compression development length L_sy,cb is the greater of:

  • 0.22 × f_sy × d_b / sqrt(f'c)
  • 0.0435 × f_sy × d_b

Refined compression length L_sy,c applies factor k_6 = 0.75. For unyielding bars, L_sc uses the actual bar stress sigma_s rather than yield.

Outputs

The calculator reports L_sy,tb, L_sy,t, L_st, L_sy,cb, L_sy,c, and L_sc. The maximum development length L_s,max across all conditions is also shown. All factor values and governing AS 3600:2018 clause references appear in the output.

Assumptions

Reinforced concrete beam with yield strength limited to 65 MPa. Bundled bars are not used in tension. No multiplication factor for bends or standard hooks in compression is applied.

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Frequently asked questions

What design standard does this calculator use?
The calculator applies AS 3600:2018 incorporating Amendment 2 for development length calculations. It implements the provisions of AS 3600:2018 Section 13 - Development and splices of reinforcement, including the basic development length formula and all applicable modification factors (k1 through k7).
What are the key inputs?
Key inputs are concrete compressive strength (f'c), bar diameter and grade (N or L reinforcement), cover to the bar being developed, transverse reinforcement details (bar size and spacing), bar geometry (straight or standard hook), and application type (top bar, bottom bar, or compression). For hooked bars, the hook geometry and cover details are also required.
What does the calculator output?
Outputs include the basic development length (Lsy.t or Lsy.c) and the final design development length after applying all applicable modification factors. For hooked bars, the development length to the back of the hook and the minimum embedment are also reported. All AS 3600:2018 clause references and factor values are shown in the output.
What modification factors does the calculator apply?
The calculator applies the AS 3600:2018 Section 13 modification factors: k1 (bar position - top bars with more than 300mm concrete below), k2 (concrete density), k3 (bar size and transverse reinforcement), k4 (transverse confinement pressure), and k5 (excess reinforcement). For compression bars, the equivalent compression factors are applied.
Can I use this calculator for lapped splices?
Development length is the basis for lap splice design per AS 3600:2018 Section 13.2.3. The design lap length is calculated as the development length multiplied by a factor for the proportion of bars spliced (1.0 for 50% or less spliced, 1.3 for more than 50%). Enter the development length from this calculator to determine the required lap length for your splice configuration.

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