Reinforcement Development Length Calculator to AS 3600: Tension and Compression Bars

How this calculator works

Enter the bar diameter, the yield strength, the concrete strength and the cover or half spacing, and whether it is a top bar.

The calculator finds the factors k1 (position), k2 = (132 - db)/100 and k3 = 1.0 - 0.15 (cd - db)/db limited to 0.7 to 1.0, then the tension development length Lsy.t = 0.5 k1 k3 fsy db over k2 root f'c, not less than 29 k1 db.

It also gives the compression development length of clause 13.1.5.3.

Formulas used

• L_{sy.t} = \max\left\{\frac{0.5k_1k_3f_{sy}d_b}{k_2\sqrt{f'_c}},\ 29k_1d_b\right\}
• k_2 = \frac{132 - d_b}{100}
• k_3 = 1.0 - 0.15\frac{c_d - d_b}{d_b}
• L_{sy.c} = \max\left\{\frac{0.24f_{sy}d_b}{\sqrt{f'_c}},\ 0.043f_{sy}d_b\right\}

Worked example

With the default numbers in the calculator above:

1. Factor k1 for the position of the bar (AS 3600 cl 13.1.2.2): 1.00 (normal position)
2. Factor k2 for the bar size (AS 3600 cl 13.1.2.2): 1.12
3. Factor k3 for the cover and spacing (AS 3600 cl 13.1.2.2): 0.85
4. Basic development length in tension (AS 3600 cl 13.1.2.2): 670.80 mm (33.54 bar diameters)
5. Development length in compression (AS 3600 cl 13.1.5.3): 430.00 mm (21.50 bar diameters)
6. Tension length rounded up to the next 10 mm: 680.00 mm

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: Position of the bar Top bar: horizontal, with more than 300 mm of concrete cast below it.

1. Factor k1 for the position of the bar (AS 3600 cl 13.1.2.2): 1.30 (a top bar, with more than 300 mm of concrete cast below)
2. Factor k2 for the bar size (AS 3600 cl 13.1.2.2): 1.12
3. Factor k3 for the cover and spacing (AS 3600 cl 13.1.2.2): 0.85
4. Basic development length in tension (AS 3600 cl 13.1.2.2): 872.05 mm (43.60 bar diameters)
5. Development length in compression (AS 3600 cl 13.1.5.3): 430.00 mm (21.50 bar diameters)
6. Tension length rounded up to the next 10 mm: 880.00 mm

Common questions

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Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: AS 3600:2018 Concrete structures, clause 13.1; AS/NZS 4671 Steel for the reinforcement of concrete.

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