Liner Type: Reinforced Concrete

In the Define Liner Properties dialog, choose Liner Layer Type = Reinforced Concrete. The Reinforced Concrete liner type greatly simplifies the task of modeling composite two-component liner systems such as reinforced concrete, or steel sets and shotcrete.

• The reinforcement component is typically steel (e.g. rebar, I-beam, lattice girder)
• The "concrete" component may represent concrete, shotcrete or other material

The properties of the reinforcement and the concrete are defined separately in the input dialog. For analysis purposes, RS3 uses this input data to determine a homogeneous beam cross-section which has properties equivalent to the actual reinforced liner.

The Reinforced Concrete liner type in RS3 was designed to be used as an Elastic support material. Although a Plastic material option is provided, in most cases you should use the Elastic option, as discussed below.

Like a Standard Beam liner, a Reinforced Concrete liner is made up of beam elements which respond to flexural, axial (compressive or tensile) and shear loads. In fact the RS3 analysis engine does not distinguish between a Standard Beam liner and a Reinforced Concrete liner, given equivalent properties. The primary difference between the two liner types is the input data and the output of results.

To define the properties of a Reinforced Concrete liner:

1. Enter the reinforcement and/or concrete properties described below.
2. You can turn OFF either the reinforcement or the concrete component of the liner by clearing the desired checkbox. This allows you to use the Reinforced Concrete liner option to model support which only uses one component.

Concrete Properties

First of all, note that the "concrete" component of a Reinforced Concrete liner does not necessarily have to be concrete. It may represent shotcrete or other material which surrounds the reinforcement. The name concrete was chosen for convenience as a typical matrix material for the reinforced liner.

The required Concrete properties are:

• Thickness
• Young's Modulus
• Poisson's Ratio
• Shear Strength
• Compressive Strength
• Tensile Strength

Reinforcement Properties

The reinforcement component of a Reinforced Concrete liner is typically steel (e.g. rebar, I-beam, lattice girder), but could be any material as long as the reinforcement configuration can be defined by the available input parameters.

The required Reinforcement properties are:

• Spacing
• Section Depth
• Area
• Moment of Inertia
• Young's Modulus
• Poisson's Ratio
• Shear Strength
• Compressive Strength
• Tensile Strength

Material Type

Material Type: Elastic

The Reinforced Concrete liner type in RS3 was designed to be used as an Elastic support material. In most cases you should use the Elastic material type for a Reinforced Concrete liner.

When the Material Type = Elastic, the liner will only respond elastically to loading, and there will be no upper limit to the loads which can be sustained by the liner (i.e. the liner can carry loads greater than the strength of the liner material). The strength properties of the liner are used to compute the safety factor of the liner elements and to generate support capacity envelopes which are viewed in the RS3 Interpret program.

Material Type: Plastic

In general, the use of the Plastic material type option is NOT recommended for the Reinforced Concrete liner type in RS3. The Plastic option should only be used if you specifically wish to define your liner input properties using the Reinforced Concrete liner type, and you wish to model liner yielding. However, in this case you must be aware of the following issues:

• The safety factors and support capacity plots in the RS3 Interpret program will NOT BE VALID for liner elements which have yielded, and should NOT be used for design purposes.
• The plasticity calculation for Reinforced Concrete liners involves several simplifying assumptions, which are described below.

Assumptions for Plastic Liner

1. Yielding is computed for the equivalent homogeneous cross-section, using the layering method described for the Standard Beam liner type. Actual failure mechanisms of the composite two-component Reinforced Concrete liner are NOT considered.
2. The tensile and compressive strengths of the composite liner are computed by weighting the strengths of the reinforcement and concrete according to their area. For example:

   
   sigcp = r_sigcp*Ar/(Ar+Ac) + c_sigcp*Ac/(Ar+Ac)

   where:

   sigcp = peak composite compressive strength

   r_sigcp = peak reinforcement compressive strength

   c_sigcp = peak concrete compressive strength

   Ar = Area of reinforcement per unit length of excavation

   Ac = Area of concrete per unit length of excavation

3. Both the tensile and compressive strength of the reinforcement are assumed to be perfectly plastic. This means that the residual tensile strength is equal to the peak tensile strength and the residual compressive strength is equal to the peak compressive strength.
4. For concrete, the residual tensile strength is zero and the residual compressive strength is 20% of the peak.

Include Weight in Analysis

See the Standard Beam topic as the definition of Include Weight in Analysis is the same for both Reinforced Concrete and Standard Beam liner types.

Beam Element Formulation

See the Standard Beam topic as the definition of Beam Element Formulation is the same for both Reinforced Concrete and Standard Beam liner types.

Stage Reinforced Concrete Liner Properties

Concrete properties of a Reinforced Concrete liner can be modified at different stages of a multi-stage model, by using the Stage Reinforced Concrete Liner Properties option in the Liner Properties dialog. This could be used, for example, to model the increase in strength and stiffness of shotcrete or concrete after initial placement. By selecting Define relative change based on the install stage allows for the factor to change relative to their installation stage. This would be used to define changes in strength and stiffness of a liner as it is applied in a stage excavation of a tunnel.

See the Stage Liner Properties topic for more details.