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# Changes in AS3600:2018 Amendment 2 (Concrete)

> Changes in AS3600:2018 Amendment 2 (Concrete)

# Background

A number of significant updates have been made with AS3600:2018 Amdt 2, whose key effects are on the spacing and quantity of shear fitments / ligatures required. Calcs.com has updated its calculator for consistency with this new amendment.

ClearCalc's concrete calculators affected by Amendment 2 changes are:

* L-Type Cantilever Retaining Wall
* Rectangular Concrete Beam
* Rectangular Concrete Column
* Concrete Pad Footing
* One-Way Concrete Flat Slab
* Concrete Wall Footing

## Capacity Reduction Factor (Bending Moment with compression)

1. Table 2.2.2 (d) has changed the Φ₀ factor to be equivalent to $\phi_0 = 0.65 \times k\phi$. There is a minor impact on the reduction factor where columns are slender or where $\frac{Q}{G} \leq 0.25$, refer to calculations for $k\phi$.

## Shear Strength

2. Upper limit shear strength $V_{u,\text{max}}$ has been reduced by 10% in Equation 8.2.3.3(1).

3. Factor $k_v$ (simplified method) increases the concrete shear capacity $V_{uc}$ by up to 50% from Amendment 1, in particular for thinner depth sections without reinforcement.\
   Previously a limit of $k_v = 0.10$ was placed for any beam where minimum shear reinforcement was not satisfied or no fitments were provided. This has now been increased to $k_v = 0.15$. Refer Clause 8.2.4.3(a).

## Fitment Detailing / Spacing Requirements

4. The minimum reinforcement spacing is now relaxed for beams with low shear force. Where $V^* \leq \phi V_{u,\text{min}}$, the fitments may now be spaced at 500mm or $0.75 \times D$ whereas previously 300mm or $0.5 \times D$ limit was imposed under all circumstances apart from very large beams.

5. For a short column satisfying $L < 5 \times \text{depth}$, Amendment 2 has introduced minor changes to the max allowable fitment spacing to reflect the actual fitment strength $\text{spacing} = \sqrt{\frac{f_{syf}}{500}} \times 24 \times d$ instead of $\text{spacing} = 24 \times d$ previously in accordance with Clause 14.5.4(b).

6. For beams of $\text{depth} > 300\text{mm}$, shear fitments are now required even when $V^* \leq \phi V_{uc}$. An additional factor $k_s$ has been added factoring down the upper limit shear force that may be taken without adding fitments in Clause 8.2.1.6(1).

## Renaming of Variables

7. $D_c$ is now renamed to $b$ (smaller column cross-sectional dimensions). Refer Clause 1.7.

8. $K_s$ is now renamed to $k_s$ (Beam Depth Factor to Determine Reinforcement Required). The definition of $K_s$ in Clause 1.7 has not been updated in Amendment 2 from its previous version. It is believed that this definition should be further expanded in future revisions to reflect its use in Clause 8.2.1.6(1).

## Assumptions

1. The above is not a comprehensive list of Amendment 2 changes. However, they do reflect all the changes that are relevant to calculations performed in Calcs.com.

2. Calcs.com concrete calculators utilise the Simplified Method for calculating $k_v$ and $\theta_v$ in compliance with Clause 8.2.4.1. Therefore, the Amendment 2 updates for the "General Method" in Clause 8.2.4.2 are not listed above.
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