Reinforcement Properties for LRFD

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Description

Definition of the material properties for a section or beam is a three step process:

1. Add the material type (concrete / reinforcing steel / etc.)
2. Define a set of properties for that material type (compressive strength etc.)
3. 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 reinforcement. As data is entered the program checks that values are within the expected range for steel. This check will highlight any values in error by a factor of 10 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.

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Yield strength fy

Enter the yield strength of the reinforcement. A warning will be issued if the value entered is beyond the limit of A5.4.3.1 of AASHTO LRFD 9, but the value will not be rejected.

Strength LS stress/strain distribution

To select a stress / strain curve for the reinforcement, click on this field to display a drop-down list and select from the 2 options as follows:

• Default

  This is based upon the ULS (Strength) stress strain curve defined in the UK bridge design code BS 5400. It uses what is referred to as the 0.2% offset method in the commentary to A5.4.3.1 of AASHTO LRFD 9.

• Define Linear

  To define a stress / strain relationship of the same form as the default above, but with different parameters.

Elastic modulus - Es

Enter the modulus of elasticity of the reinforcement. The default value is 200,000 MPa (29,000KSI) as given in A5.4.3.2 of AASHTO LRFD 9.

Max. Stress limitation factor

Enter the stress limitation factor for reinforcement in tension at the Service limit state.

The value entered here will affect the upper bound for the limiting tensile stress, and is not used as a substitute for the calculated value of f_ss derived from equation 5.6.7-1 of AASHTO LRFD 9.

The default value corresponds to the upper limit for crack control purposes given in equation cited above.

There is no requirement in the code for a limit to the compression stress in the reinforcement, but the program will issue an alert if the compression stress exceeds the yield strength.

Density

Enter the density of the reinforcement.

The default value is 0.49KIP/FT³ (or 76.97 kN/m3 which is equivalent to 7850 kg/m³) as given for steel in Table 3.5.1-1 of AASHTO LRFD 9.

Property name

The program will supply a reference name which should provide a nearly unique identifier to the material property set which is usually unique. This value may be edited to give a more readily recognizable name if required.

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