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Ground acceleration

Use the Ground acceleration tool to change the behaviour and parameters of the ground acceleration function.

Ground acceleration tool

When you select the Ground acceleration tool from the panel, a new dialogue window opens. This dialogue window has multiple tabs.

Diagrams​

Ground acceleration diagrams dialogue window

In the Diagrams tab, you can define so-called ground acceleration functions (also known as "accelerogram") in time and in horizontal/vertical direction

List of diagrams​

In the top left is a list with all inserted diagrams. Below that list you have 3 buttons:

  • New - add a new diagram
  • Delete - delete an existing diagram
  • Modify - modify an existing diagram

When you select New or Modify, a new dialogue window opens.

Ground acceleration diagrams dialogue window

  • Name - add or change the name of the diagram
  • Horizontal - define the diagram for horizontal movement
  • Vertical - define the diagram for vertical movement
Time-acceleration data​

In the middle of the left hand side, you can see a table with the time and acceleration values for each diagram you select from the top list. You can enter new values or change existing values.

  • t - add or change time value
  • a/g - add or change the acceleration value
Import/Export time-acceleration data​

When you click Import/Export> button in the bottom of the time-acceleration table, a new menu opens.

Import/export menu

  • Save - save the time-acceleration table to a file to use later
  • Load - load the time-acceleration table from a file
  • Copy table - copy the time-acceleration table to the clipboard
  • Paste table - paste the time-acceleration table from the clipboard
Generate time steps for time-acceleration data​

When you click the Generate steps button (marked with asterisk *) in the bottom of the time-acceleration graph, a new dialogue window opens, where you can generate time steps for the time-acceleration table.

Generate steps dialogue window

  • Δ t - time step size
  • Number of steps - number of time steps
Time-acceleration graph​

On the right hand side, you can see the time-acceleration graph that was generated from the table. Below the graph you have 6 buttons:

  • Response spectra - use this button to open a new dialogue window where you can generate acceleration response spectra based on the time-acceleration table. Read below in more detail.
  • < - use the Left button to move left on the graph
  • < > - use the Zoom in button to zoom into the left side of the graph
  • >< - use the Zoom out button to move zoom out of the graph
  • |< >| - use the Zoom all button to fit entire graph on the window
  • > - use the Right button to move right on the graph

Combinations​

Ground acceleration combination dialogue window

In the Combinations tab, you can combine the ground acceleration diagrams (defined at Diagrams tab) by time steps and directions with given multiplication factors.

  • Name - add or change the name of the combination
  • dt - numerical integration time step
  • Dir - indication for the direction of the movement
  • Factor - set the multiplication factor for each direction
  • Diagram - select a suitable diagram from the dropdown menu

Add to documentation​

You can add all the relevant seismic load data to the documentation by using the button Add to documentation.


Generating response spectra from time-acceleration data​

When you press the Response spectra button in the bottom of the time-acceleration graph, a new dialogue opens. In this dialogue, you can calculate horizontal and vertical ground spectra from previously defined time-acceleration diagrams. You can also send the ground spectra to the Seismic load spectra. This dialogue window has multiple tabs.

Calculation parameters​

Seismic load vertical spectra dialogue window

Here you can set parameters for the calculation of the spectra.

  • Newmark - choose the Newmark integration scheme

  • Wilson-θ - choose the Wilson-θ integration scheme

  • ξ - change the damping factor

  • Δ ti - change the integration time step

  • Δ T - change the result time step

  • T end - change the end time of the integration

  • q - change the behaviour factor


In the bottom of the dialogue window are two buttons:

  • Calculate - calculate the horizontal and vertical spectra using the calculation parameters and selected horizontal and vertical time-acceleration diagrams
  • Set spectrum - set the calculated spectrum to Seismic load spectra as Unique
note

To read about seismic load see the topic
User interface ➔ Tab menus ➔ Loads ➔ Panel Dynamic load ➔ Seismic load


Horizontal and vertical spectra​

Seismic load vertical spectra dialogue window

The tabs for Horizontal spectra and Vertical spectra are similar and contain similar tools, parameters and graphs.

In the top left on both tabs is a list with all relevant diagrams (only horizontal diagrams for Horizontal spectra tab and only vertical diagrams for Vertical spectra tab). Click on one to select it for the calculation.

On the left hand side, you can see a table with the time and acceleration values for each diagram you select from the top list. You can enter new values or change existing values. The values are also automatically filled after you press the Calculate button.

  • t - add or change time value
  • a/g - add or change the acceleration value

On the right hand side, you can see the time-acceleration graph that was generated from the table.


Last update: 2025-10-07