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This page is devoted to *frequently asked questions* (FAQ) related to [acceleration|Acceleration].
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h2. Acceleration load calculation

*Question:* How does SAP2000 calculate and apply acceleration load?

*Answer:* Please see the [acceleration load|Acceleration load] article for response.

h2. Rotational acceleration load calculation

*Question:* What procedure does CSI Software use to calculate rotational acceleration load?

*Answer:* Please see the [acceleration load|Acceleration load] article for response.

h2. Difference between relative and absolute acceleration

*Question:* The 'Display > Show Plot Functions' menu presents options for either relative or absolute acceleration. What is the difference between these options?

*Answer:* Relative acceleration is within the reference frame of the structure. Absolute acceleration is within a universal reference frame, and given as the sum of relative acceleration and ground acceleration.

h2. Manual application of acceleration load

*Question:* Can acceleration loads only be applied to selected members in the model?

*Answer:* CSI Software automatically generates and envelopes a set of acceleration loads for translation along, and rotation about, each global axis. These acceleration loads are applied at each node and element, and used to simulate ground motion during [time-history|Time-history analysis] and translation-only [response-spectrum|Response-spectrum analysis] analyses. They are also useful as starting load vectors for [Ritz-vector|Ritz vectors] analysis.

Users may manually assign acceleration loads to specific nodes and elements. Similar to [load -case|Load case] assignment, these loads are applied through an Analysis Case.

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*Previous page content:*

This page contains frequently asked questions related to *[acceleration|kb:acceleration]*.

*General FAQ*

*How does SAP2000 calculate and apply acceleration loads?*

_[See acceleration load page.|Acceleration load]_

*What is the procedure used for calculating rotational acceleration loads?*

*Question:* What is the exact procedure the program uses to calculate the rotational acceleration loads? For translational acceleration loads, the loads are calculated as negative translational mass times the acceleration. For rotational acceleration loads how exactly is the translational mass, rotational mass, or both masses used to calculate the acceleration loads?

*Answer:* _[See acceleration load page.|Acceleration load]_

*Under "Display > Show Plot Functions" menu command, absolute or relative acceleration (velocity or displacement) can be chosen. What is the difference between relative and absolute responses?*

Relative acceleration is acceleration relative to the ground. Absolute acceleration is the sum of relative acceleration and the input ground acceleration.

*Can I apply acceleration loads only to selected members in the model?*

If you need to apply acceleration loads only to some elements in your model, you would need to apply these loads manually.

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