A time diagram can be used to define the relation between load and time. The time history analysis using time diagrams is thus dependent on the defined static load.
The time diagrams used in the model are managed in the Time Diagrams dialog box.
Definition type
Two definition types are available for selection in the list in this dialog section:
- User-defined
- Function
The remaining dialog sections are adapted to the definition type.
User-defined
For a user-defined time diagram, you can specify the diagram's characteristic values in a table in the 'Timers & Multipliers' dialog section.
In the table, enter the 'time' t with the corresponding 'multiplier' k row by row. The entered rows may be in any order. This way, you can retroactively add value pairs that lie between already defined values.
Since a consistent time diagram must be available, the values are displayed in red if they are out of order. In this case, use the
button to sort the rows in ascending order.
Use the
button to delete the selected table row.
The
button allows you to import the table values of a diagram from Excel. Click the
button to export the user-defined time diagram to Excel.
The functions for saving user-defined time diagrams in a library and importing them again from there are still under development. Therefore, the
buttons are locked.
If the value pairs have a constant time interval, activate the Δt check box below the table. Then, enter the time step in the text box to the right of
. When you enter multipliers in the table now, the time is automatically applied with the steps Δt. You can adjust the step Δt at any time in order to enter further value pairs with a different time step. This function is described in the
Accelerograms
chapter.
The diagram created from the specifications is shown in the lower section. The options for 'Diagram start' and 'Diagram end' are described in the Function section.
Function
The second definition type allows you to define the time diagram by any function. The parameter t is reserved for the time.
Enter the function over time in the 'Multiplier function' field. You can use all operators and functions as in the main program (see Chapter Formulas of the RFEM manual). In this case, you can also use the global parameters that you have defined for the input in RFEM. Click the
button to open the 'Edit Global Parameters' dialog box.
Example of periodic function
f(t) = k1 · sin (ω1 · t + φ1) + k2 · sin (ω2 · t + φ2) + ...
The 'Time Limit' tmax specifies the maximum time for the validity of the function. Changes are applied immediately in the 'Multiplier - Time Diagram'.
Below the diagram, two options are available for the 'Diagram Start' and the 'Diagram End'. This way, you can control which values should be adopted if the Time History Analysis Settings or the option of Time Slip type.
'Zero' means that all values in the negative zone or if t > tmax are set to zero. If you select 'Constant', the first or last diagram value is kept and continued. This option is useful, for example, for linear curves in order to continue the curve with the same inclination.