Concrete Properties
Description
Definition of the material properties for a section or beam is a three step process:
- Add the material type (concrete / reinforcing steel / etc.)
- Define a set of properties for that material type (characteristic strength etc.)
- Allocate the material properties defined in 1 & 2 to the relevant parts of the section or beam section component.
This form performs the second of these 3 stages for concrete. As data is entered the program checks that values are within the expected range for concrete. This check will highlight any values in error by a factor of 10 or more. The displays for Strength Limit State and Service Limit State are to the same scale, and are updated as the values in the fields are changed.
For the Strength Limit State, the stress-strain distribution is assumed to be parabolic. The parabolic shape used is generally accepted as the closest shape in substantial agreement with test results which is practical for design purposes.
Form Graphic
Related Topic
Field Help
Characteristic strength f'c
Enter the compressive strength of the concrete at 28 days.
ULS stress/strain curve parameters
To select a stress / strain curve for the concrete, click on this field to display a drop down list containing 3 options as follows:
Default 1
This is based upon the ULS stress strain curve defined in the UK bridge design code BS 5400, with due allowance made for the strengths based upon cylinder crushing tests and not cube strengths. Also the maximum strain will be taken as 0.003, and not 0.0035 (note that AS 5100.2 does not include explicit stress strain curves for concrete).
Default 2
This is based upon the ULS stress strain curve defined in the Hong Kong Highways Department design code, with the same allowances as described for Default 1 above.
Define
This may be used to define a stress / strain curve of the same form as the ones above (i.e. parabolic up to the maximum stress) but with different parameters.
Modulus of Elasticity - Ec
Enter the modulus of elasticity of the concrete under short term (instantaneous) loading.
The default value is calculated from the formula given in AS 5100.5-2017 Clause 3.1.2 (2004 Clause 6.1.2), based on the compressive strength specified above.
As elastic modulus, shear modulus and the Poisson's ratio are related, a change of this value will affect one of the three elasticity parameters, in this case the shear modulus.
Modulus of Elasticity - long term
Enter the modulus of elasticity of the concrete under long term loading.
For AS 5100.5-2017, calculation of default value is based on the actual creep coefficient per Clause 3.1.8.3. Parameters for creep coefficient can be found on the Data for Shrinkage and Creep form either for design section or design beam.
For AS 5100.5-2004, the default value is one third of the short term elastic modulus value, which corresponds to a 30 year creep factor of 2.0 (refer to Clause 6.1.2).
Poisson's Ratio, ν
Enter the value for Poisson's ratio. The default value is typical for this type of material. As elastic modulus, shear modulus and the Poisson's ratio are related, a change of this value will affect one of the three elasticity parameters, in this case the shear modulus.
Shear Modulus, G
Enter the shear modulus value. As elastic modulus, shear modulus and the Poisson's ratio are related, a change of this value will affect one of the three elasticity parameters, in this case the Poisson's ratio.
SLS Compressive stress limit factor
Enter the stress limit factor for concrete in compression. This value will be used for calculating the permissible limiting stress.
In prestressed members, for temporary stresses before losses, the limit is given in Clause 8.1.4.2 of AS 5100.5 as 0.5 for a rectangular distribution of stress, and 0.6 for a triangular distribution of stress.
No other specific limit is given in AS 5100.5, but the limits above are deemed suitable.
Limiting minimum stress
A small tensile stress may be appropriate for Serviceability Limit State analysis. Any value entered here will not affect the Ultimate Limit State analysis. The default value is zero tension which is appropriate for an elastic cracked section analysis.
For prestressed beam analysis, the value entered here will not be used. In this case the tensile stress is obtained from the specific provisions for prestressed concrete.
Coefficient of thermal expansion
Enter the coefficient of thermal expansion for use in temperature gradient calculations.
The default value is 0.000010/°C as suggested in AS 5100.5-2017 Clause 3.1.6 (or 0.000011/°C in AS 5100.5-2004 Clause 6.1.6) for normal density concrete.
Maximum nominal aggregate size
The maximum nominal aggregate size specified here is used to determine the shear parameter kv per AS 5100.5-2017 Clause 8.2.4.2.
Density
Enter the density of the concrete. This is used in the calculation of self-weight moments, and in the calculation of mass when beams are incorporated into a dynamic analysis.
The default value is 23.54 kN/m3 which corresponds to 2400 kg/m3 as given in AS 5100.5-2017 Clause 3.1.3 (2004 Clause 6.1.3) for normal weight concrete.
Where the actual density is greater than this the tension stresses for pre-tensioned beams at transfer may be unduly conservative.
The value may depend upon the type of aggregate, the amount of reinforcement, and the degree of compaction.
Property name
The program will supply a reference name which provides an identifier to the material property set which is usually unique. This value may be edited to give a more readily recognisable name if required.