AS 3600-2001 and AS 3600-2009 Development Lengths

For a user-defined bar, the effective development for any point along the bar is calculated in accordance with the following figure.

Effective development at any point along a bar for the undisplaced moment diagram (for AS3600-2001 and 2009 only)

The end of any user defined bar that is close to a slab edge such that it could not be extended and that has a 180 degree hook will use a desired extension length of zero. For other situations, the desired extension length is D, the overall depth of the member
For any length less than the desired extension length D, the effective development is zero.
For any length greater than or equal to the additional extension length, but less than the full development length, the effective percentage development is (provided length - desired extension length) / (full development length) x 100%. This is accomplished by considering a fraction of each bar developed.

For a program designed bar, when the bar is detailed the bar will be extended the full development length plus the desired extension length. If a bar is unable to be extended this full desired length, RAM Concept will attempt to extend the bar the 90 degree hook development length plus the desired extension length, then the 180 degree development length plus the desired extension length, then the 180 degree development length with no extension length. If there is not enough extension space to satisfy any of these conditions, an "anchor" will be placed at the end of the bar and it will be considered fully developed from that point.

AS 3600-2001

Basic straight tension development length is calculated using equation 13.1.2.1(a). The following factors are used in this equation:

k₁ = reinforcement location factor
- "concrete below" is taken as the depth from the bar center to the bottom of the concrete section
- 1.25 for concrete below > 300 mm
- 1.0 for concrete below ≤ 300 mm
k₂ = 2.4 (conservatively)
f_sy = yield stress of bar
A_b = cross sectional area of reinforcing bar
2_a + d_b = twice the vertical distance from the nearest concrete surface to the center of the bar

In addition, the following factors (from ACI 318) are applied:

coating factor
- 1.5 for epoxy coated bars with cover (to center of bar) less than 3d_b (spacing is not calculated)
- 1.2 for all other epoxy coated bars
- 1.0 for uncoated bars
lightweight aggregate concrete factor:
- 1.3 for concrete density ≤ 1900 kg/m³
- 1.0 for concrete density > 1900 kg/m³

For development of standard hooks, basic tension development length is calculated as half the straight tension development length in accordance with Clause 13.1.2.4.

In accordance with 8.1.8.1, the extension length used for this Code is the overall depth of the section. This extension is applied in addition to the required development length. RAM Concept applies the extension length to satisfy the Code provision requiring the displacement of the bending moment envelopes by a distance D. There are some noteworthy differences between RAM Concept 's approach and the Code provision:

In most circumstances, extending the bar by a distance D beyond the required development length will satisfy the intent of the Code.
Near the ends of members, where the displaced moment diagram would cause an increased design moment, RAM Concept will design for the unmodified moment diagram, but will still ensure proper development is satisfied.

AS 3600-2009

Basic straight tension development length is calculated using equation 13.1.2.2. The following factors are used in this equation:

k₁ = reinforcement location factor
- "concrete below" is taken as the depth from the bar center to the bottom of the concrete section
- 1.3 for concrete below > 300 mm
- 1.0 for concrete below ≤ 300 mm
k₂ = (132 - d_b)/100
f_sy = yield stress of bar
c_d = assumed to be the vertical clear cover, implying that the minimum bar clear spacing is greater than or equal to twice the clear cover

In addition, the following factors are applied:

coating factor
- 1.5 for epoxy coated bars
- 1.0 for uncoated bars
lightweight aggregate concrete factor:
- 1.3 for concrete density ≤ 2100 kg/m³
- 1.0 for concrete density > 2100 kg/m³

For development of standard hooks, basic tension development length is calculated as half the straight tension development length in accordance with Clause 13.1.2.6.

In accordance with 8.1.10.1, the extension length used for this Code is the overall depth of the section. This extension is applied in addition to the required development length.