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Standard Beam versus Reinforced Concrete

In the Define Liner Properties dialog, you can choose either Standard Beam or Reinforced Concrete for modeling a liner with flexural rigidity. The Standard Beam is the original liner beam element used in RS3. The Reinforced Concrete option, introduced in version 2, offers most of the features of the Standard Beam model, plus many additional capabilities.

The differences and similarities between the Standard Beam and Reinforced Concrete liner types as defined in RS3 are summarized below.

Input Data

The Standard Beam input data simply requires the beam thickness (or area/moment of inertia) to define the beam cross-section.

The Reinforced Concrete input data allows you to provide detailed properties of the reinforcement (e.g. steel) as well as the matrix material (e.g. concrete). The Reinforced Concrete liner type has additional input data options not available with Standard Beam.

  • You can turn OFF either component of the liner (i.e. reinforcement or concrete) to model support systems which only use one component (e.g. unreinforced shotcrete, or steel sets without shotcrete).
  • The Reinforced Concrete liner type offers a built-in database of common reinforcement types, which can be customized. You can select a reinforcement type from the database and the properties will be automatically loaded into the liner properties dialog. This database is not available for Standard Beam.

Elastic Response

Both Standard Beam and Reinforced Concrete are beam elements which can support axial, shear and bending loads.

The RS3 analysis engine does not distinguish between Standard Beam and Reinforced Concrete beam elements, for an elastic liner. The properties of a Reinforced Concrete liner are used to determine an equivalent rectangular beam section which has the same elastic response as the reinforced liner (i.e. the analysis engine does not actually see the individual components of the reinforced liner, only an equivalent simple liner).

You can define a liner with equivalent elastic properties using either Standard Beam or Reinforced Concrete, and you will get exactly the same response (see below for more information).

Plastic Response

A Standard Beam liner can be defined as Plastic and will yield if the strength envelope is exceeded. Residual strength properties can be specified, so that if the peak strength is exceeded, the beam element can still carry loads.

A Reinforced Concrete liner can also be defined as Plastic, and will give the same response as a Standard Beam liner, for an equivalent set of properties. However if you allow yielding for a Reinforced Concrete liner, the support capacity plots and safety factor results will be meaningless for yielded liner elements. Also, Several assumptions are used in the plasticity calculation for Reinforced Concrete liners, as discussed in the Reinforced Concrete liner topic. So although a Plastic option is provided for Reinforced Concrete, it is not recommended unless you do not intend to use the support capacity plots.

Analysis Results

You can plot axial force, shear force and bending moment for both Standard Beam and Reinforced Concrete liners.

For Reinforced Concrete you can plot results for each component separately (i.e. reinforcement and concrete). Results for the two components of Reinforced Concrete are back-calculated from the overall liner results, using a methodology described in (reference).

The main purpose of the Reinforced Concrete liner option is to allow liner design based on the elastic response plotted on support capacity plots. This allows the designer to easily visualize overstressed beam loads in relation to the theoretical failure envelopes, and to compute factors of safety for the liner components. Support capacity plots and safety factor are only available for Reinforced Concrete and NOT for Standard Beam. See the Support Capacity Plot topic for details.

Equivalent Properties

When you define the properties of a Reinforced Concrete liner, RS3 automatically calculates the elastic properties for an equivalent Standard Beam liner. The equivalent properties which are computed are:

  • equivalent Young's modulus
  • equivalent Thickness
  • Poisson's ratio (always equal to zero due to the method of calculation)

The equivalent properties assume a uniform homogeneous rectangular beam cross-section. The equivalent properties can be found listed in the Info Viewer information and in the popup Data Tips display for liner properties. For a Reinforced Concrete liner, the equivalent properties are the properties that are actually used by the RS3 compute engine during the analysis.

NOTE: if you define a Standard Beam liner using the equivalent property values of a Reinforced Concrete liner, you should get exactly the same elastic results as the Reinforced Concrete liner.

Why Use Standard Beam?

Why would you use Standard Beam when the Reinforced Concrete liner type offers many additional features?

  1. The Standard Beam liner type is the original liner beam element in RS3, and must be maintained for compatibility with existing files which use this liner type.
  2. The data input for Standard Beam is simple. If you only need to model a simple liner (e.g. a layer of shotcrete) then it is sufficient to use the Standard Beam liner type.

Why Use Reinforced Concrete?

The primary reasons for using the Reinforced Concrete option are:

  1. The Reinforced Concrete liner type allows you to specify the properties of the reinforcement and concrete separately.
  2. The reinforcement database makes it easy to choose a reinforcement type and enter the reinforcement properties.
  3. Analysis results can be plotted for the reinforcement and concrete components of the liner, including support capacity plots and safety factor.
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