AS 3600-2018 Material Behaviors

This section explains how RAM Concept models the concrete, non-prestressed reinforcement and prestressed reinforcement when using AS 3600-2018.

Concrete Behavior

You define the concrete elastic modulus in the materials window. You can choose to use code equation 3.1.2 or a specified value.

When you directly specify values, there must be two elastic modulus values:

E_ci = value for initial service (transfer) cross section analyses
E_c = value for all other conditions

When the AS 3600-2018 code section is selected the following values are used:

E_{c} = \begin{matrix} ρ^{1.5} 0.043 \sqrt{f_{c m i}} & when & f_{c m i} \leq 40 MPa \\ ρ^{1.5} 0.024 \sqrt{f_{c m i}} + 0.12 & when & f_{c m i} > 40 MPa \end{matrix}

where

f_cmi

mean value of cylinder strength at stressing. Determined using Table 3.1.2.

For calculations based on the gross section, concrete is assumed to be a perfectly linear-elastic material with no stress or strain limits.

See Concrete Stress-Strain Curves for a description of the stress-strain curves used in a detailed cross section analysis. The maximum stress used in the concrete stress-strain curves is 0.9 f’c per clause 3.1.4(b).

The strength stress-strain curves are truncated at a strain of 0.003. The other stress-strain curves have no limit strain.

(Non-prestressed) Reinforcement Behavior

This material is described in Non-prestressed Reinforcement Stress-Strain Curves in "Section Design Notes".

Bonded Prestressed Reinforcement Behavior

This material is described in Post-tensioning Material Stress-Strain Curves and Relationship of Bonded Post-tensioning Strains to Cross-Section Strains in "Section Design Notes".

Unbonded Prestressed Reinforcement Behavior

For service conditions, RAM Concept assumes that unbonded tendon stresses are not affected by cross section strains.

For ultimate resistance moment calculations, RAM Concept ’s general approach to unbonded tendon stress-strain curves is detailed in Unbonded Post-tensioning Stress-Strain Curves – Program Implementation .

For AS 3600-2018, the maximum unbonded tendon stress, f_limit, is defined by section 8.1.8. In the calculation of b_efd_p, RAM Concept assumes the tendons are placed on the more beneficial side of the cross-section centroid (the same limiting stress value is used for both positive and negative moment capacity calculations at each cross section).