Time-Dependent Properties of Concrete

This chapter describes the "Concrete" and "Reinforcing Steel" material categories, which are important for the concrete design.

Concrete

Once you activate the concrete design, additional tabs appear in the "Edit Material" dialog box for concrete materials, where you can make important settings for the concrete design. The general description of this dialog box can be found in Chapter Materials of the RFEM manual.

Time-Dependent Properties of Concrete

Time-Dependent Properties of Concrete

Settings

To include "creep" and "shrinkage" in the design, activate the corresponding option in this section. Further specifications are then taken into account for all structural components with the material assigned. If the creep and shrinkage are deactivated, it is not possible to enter further data in the tab.

Specify the "Relative humidity of ambient environment", the "Concrete age at end of curing", and "Age of concrete at loading". Based on this information, the program determines the creep coefficient φ and the shrinkage strain ε.

Modification of Concrete Curing

If activating the Creep, you can use the options in the list to modify the concrete maturation process (see the image Time-Dependent Properties of Concrete). These affect the determination of the creep coefficient φ.

• None: There is no adjustment of the creep coefficient φ.
• Temperature Treatment: Click the button einen neuen Dialog auf. There, you can define the concrete temperature dependent on time. These parameters influence the equivalent concrete age t_0,e. As soon as you have activated the modification using the temperature treatment, you can specify the "Creep Coefficient φ_e at equivalent time" in the Function Data section.

Defining Temperature Dependence on Time

• Measurement of Modulus of Elasticity: In case the modulus of elasticity of the concrete was measured on test specimens, you can use this option to replace the calculated value of the creep coefficient φ by the measured value. Enter the "Measured modulus of elasticity" of the test specimen and the "Concrete age" at the time of measurement. Based on this information, the program determines the equivalent concrete age t_0,e, which again modifies the creep coefficient to φ_e.

Modification Type "Measurement of Modulus of Elasticity"

• Measurement of Concrete Strength: This modification option is similar to the option described above. Instead of the measured modulus of elasticity, enter the concrete compressive strength f_cm(t), which was measured at a certain point in time t.

Function Data (Only for Visualization)

In this section, you can define a cross-section or a thickness of the model and select a "function type" that is shown in the table on the right and in the diagram below.

Selecting Function Type: Creep Coefficient or Shrinkage Strain

This allows you to control whether the creep coefficient φ or a type of shrinkage strain (total shrinkage strain ε_cs or its components drying shrinkage ε_cd and autogenous shrinkage ε_ca) are displayed as ordinates. Thus, you get the information about the course of the long-term effects in conjunction with the various settings; for example, for concrete maturation.

The results shown depend on a certain "thickness" or a "section".

Selecting Object Type: Thickness or Section

In the "Number of steps" n_s text box, you can adjust the division for the table and the diagram. Ten division points are set by default, so the table has eleven result rows.

The "Age of concrete at the considered moment" t is preset to 50 years; this value is converted into days. If necessary, it is also possible to adjust the values here.

The note "only for visualization" in the title of the section means that only the input parameters for the selected cross-section or the selected thickness are specified and visualized with these values. This allows you to check the influence of the respective parameters. For the calculation, however, the creep coefficients and shrinkage strains are calculated separately at the actual design time. This is particularly relevant for the Time-Dependent Analysis (TDA) add-on (still under development).

Graph

In this section, the function data are shown as a diagram.

Creep Coefficient - Time Diagram

If you move the mouse along the graph, the respective abscissas and ordinates appear. Use the mouse wheel to zoom, use the left mouse button to move the diagram, and double-click the mouse wheel to restore the overall view of the diagram.

There are several buttons below the diagram. You can use the können Sie die errechneten Kriech- und Schwindparameter in einem Dialog anzeigen lassen.

Calculated Time-Dependent Parameters

Mit den Optionen der Listenschaltfläche ist es möglich, die Ordinate und Abszisse in einer linearen oder logarithmischen Skala darzustellen.

Logarithmic Display of Shrinkage Strain - Time Diagram

It is also possible to print the diagram. The list button haben Sie folgende Möglichkeiten:

• Print Immediately
• Print Graphics to Printout Report
• Print Graphics to PDF
• Print Graphics to Clipboard
• Print Graphics to File

The various functions are described in Chapter Graphics of the RFEM manual.

You can use the können Sie die Tabellenwerte des Diagramms nach Excel exportieren.