Materials

Materials are required for defining cross-sections. The material properties are included in the stiffnesses of members.

Dialog Box "New Material"

Name

You can define any name for the material. If the name matches an entry in the library, RSTAB imports the stored material properties. To select the material in the library, click the button at the end of the input field. The import of materials is described in the Material Library chapter.

For materials from the library, the 'Basic Material Properties' are fixed and cannot be changed. If you want to use user-defined material properties, check the User-Defined Material check box in the 'Options' section (see the User-Defined Material section).

Base

The Base tab manages the basic material parameters. It also provides control options for special properties that you can define in additional tabs.

Categories

In this section, you define the material type and the material model.

Material Type

The material type controls which parameters and coefficients are relevant for the design. This classification also specifies the partial safety factors of the material that are considered in the design depending on the standard.

For a material from the library, one of the following material types is preset.

Material Types

Material Model

The list provides the material models 'Isotropic | Linear Elastic' and 'Isotropic | Timber | Linear Elastic (Members)' (for timber materials).

Selecting Material Model

Isotropic | Linear Elastic

The linear-elastic stiffness properties of the material are independent of the direction. They can be described as follows:

The following conditions apply:

• E > 0
• G > 0
• ν > -1

Isotropic | Timber | Linear Elastic (Members)

This material model is available for materials of the 'Timber' type. With this, you can, for example, model the properties of an OSB panel in a member model that captures the different stiffnesses depending on the installation position. You can define the panel position in the 'Isotropic | Timber | Linear Elastic (Members)' tab using the two lists.

Parameters of Isotropic Linear Elastic Timber Material for Members

Basic Material Properties

This section of the 'Base' tab provides the most important material properties.

Section "Basic Material Properties"

Modulus of Elasticity

The modulus of elasticity describes the relation between axial stress and strain.

Shear Modulus

The shear modulus G, also called modulus of rigidity, is the second parameter for describing the elastic behavior of a linear, isotropic, and homogeneous material. In this case, the deformation is based on a shear stress.

Poisson's Ratio

Poisson’s ratio ν is required for determining the lateral contraction. For isotropic materials, Poisson’s ratio is usually between 0.0 and 0.5. From a value of 0.5 (e.g., rubber), it is therefore to be assumed that no isotropic material is present.

The relation between modulus of elasticity, shear modulus, and Poisson’s ratio for an isotropic material is described in Equation Poisson's Ratio.

If you enter a User-Defined Material with its isotropic properties, RSTAB determines Poisson’s ratio from the values of the modulus of elasticity and shear modulus. If necessary, you can change this default setting in the 'Definition Type' list.

Definition Type

Specific Weight / Density

The specific weight γ describes the weight of the material per unit volume. This specification is particularly important for the "Self-Weight" load case: The automatic self-weight of the model is determined from the specific weight and the cross-sectional areas of the members used.

The density ρ describes the mass of the material per unit volume. This specification is required for dynamic analyses.

Coefficient of Thermal Expansion

The coefficient of thermal expansion α describes the linear relation between temperature and length changes (strain of the material when heated, compression when cooled).

The coefficient of thermal expansion is relevant for the 'Temperature' and 'Temperature Change' load types.

Options

The check boxes in this section of the 'Base' tab allow you to influence the material properties. After activating an option, new tabs are added.

Section "Options"

User-Defined Material

For materials from the library, the material properties are fixed. Therefore, they cannot be changed directly in the input fields. To adjust the properties of a material, activate the 'User-Defined Material' check box. This makes the input fields of the basic material properties in the 'Base' tab accessible. Likewise, you can change the design-relevant properties in the 'Material Values' tab (see the Adjust material properties image). In the 'Stiffness Modification' tab, you can scale the modulus of elasticity and shear modulus globally with a factor (see the Adjust material stiffness image).

Temperature-Dependent

To define a linear elastic material with temperature-dependent stress-strain properties, activate the 'User-Defined' and 'Temperature-Dependent' check boxes. You can then define the temperature-dependent material properties in the Temperature-Dependent tab.

Cost Estimation

For the cost determination, the materials assigned to the individual objects are used. You can define the unit costs and units of the objects in the Cost Estimation tab.

CO₂ Emissions Estimation

The CO₂ emissions estimation is also based on the materials assigned to the individual objects. You can define the unit emissions and units in the CO₂ Emissions Estimation tab.

User-Defined Texture

With a user-defined texture, you can assign a surface structure to the material. The objects are then displayed very realistically in the rendering. In the 'User-Defined Texture' tab, select an existing entry or use the button to define a new texture (see the Textures chapter).

Material Values

The Material Values tab provides all material properties that play a role in the structural analysis and the design in the add-ons.

Adjusting Material Properties

Stiffness Modification

The Stiffness Modification tab is displayed if you have checked the User-Defined Material option in the 'Base' tab. Here, you can globally adjust the stiffness of the material, for example to consider safety factors or reduced material properties.

Adjusting Material Stiffness

The list in the 'Modification Type' section provides two options:

• Division factor for moduli of elasticity and shear moduli
• Multiplication factor for moduli of elasticity and shear moduli

In the 'Parameters' section, enter the factor by which the material stiffness is to be adjusted.

Temperature-Dependent

The Temperature-Dependent tab is displayed if you have checked the User-Defined Material and Temperature-Dependent options in the 'Base' tab. Here, you can describe the temperature-dependent material properties. The temperature-dependent material properties are considered for objects that are thermally loaded by temperature or temperature change. When calculating the temperature loads, the final temperature of the respective step is applied.

Defining Temperature-Dependent Material Properties

In the 'Temperature-Dependent Property' list, select a material property, for example the modulus of elasticity. Then use the button to create the required table rows so that you can enter the temperatures with the associated values row by row. The button also allows you to import the data from an Excel table.

The 'Reference Temperature' defines the stiffnesses for objects that have no temperature loads. With a reference value of, for example, 300 °C, the reduced modulus of elasticity of this point of the temperature curve is applied to all members.

User-Defined Material Library

You can save a user-defined material in a library as a template. This way, you do not need to define the material properties again in other projects.

Save Material

To save the current material as a user-defined material, click the button at the bottom of the 'Basic Material Properties' section after defining the material properties.

Saving User-Defined Material in Library

The 'New User-Defined Material' dialog box appears.

Dialog Box "New User Material"

In the 'Name' field, enter the name of the material. If necessary, you can also adjust the material properties. Then click OK to save the user-defined material in the library.

Import Material

To import a user-defined material from the library, click the button in the 'Basic Material Properties' section.

Importing User-Defined Material from Library

The 'Edit User-Defined Material' dialog box appears. In this library with your saved materials (see the 'New User-Defined Material' dialog box image), you can select the appropriate entry and then apply it with OK.

If you have imported a user-defined material and want to change the properties in general, you can adjust the material properties in the library using the button (in the 'Basic Material Properties' section).

Cost Estimation

The Cost Estimation tab is displayed if you have checked the Cost Estimation option in the 'Base' tab.

Specifying Unit Costs and Units for Material

For the 'Members' structural objects, check which material parameter is relevant for the cost estimation in each case: weight, volume, or area.

In the 'Unit Costs' column, enter the value that one unit of the material costs. The list in the 'Unit' column provides various options for the unit costs.

From the unit costs and the properties of the members assigned to the material, the program determines the proportional costs directly.

The 'Total Weight' at the end of the table shows the mass resulting from the summation of all activated partial weights of the material. Furthermore, the proportion of the total weight that this material has in the mass of all materials activated for the cost estimation is displayed.

The 'Total Costs' show the price resulting from the summation of all activated partial costs of the material. Furthermore, the proportion of the costs that this material has in the total price of all materials activated for the cost estimation is displayed.

The 'Overall Costs' result from the addition of the total costs of all materials activated for the cost estimation.

CO₂ Emissions Estimation

The CO₂ Emissions Estimation tab is displayed if you have checked the CO₂ Emissions Estimation option in the 'Base' tab.

Specifying Unit Emissions and Unit for Material

For the 'Members' structural objects, check which material parameter is relevant for the CO₂ emissions estimation in each case: weight, volume, area, etc.

In the 'Unit Emission' column, enter the value that one unit of the material causes in CO₂. The list in the 'Unit' column provides various emission units for CO₂ equivalents.

From the unit emissions and the properties of the structural objects assigned to the material, the program determines the proportional CO₂ emissions. Thus, the calculation is performed directly and not via a separate function as in other add-ons.

The 'Total Emission' shows the CO₂ equivalents resulting from the summation of all activated partial emissions of the material. Furthermore, the proportion of the emissions that this material has in the total emissions of all materials activated for the estimation is displayed.

The 'Overall Emission' results from the addition of the total emissions of all materials activated for the CO₂ emissions estimation.