Translational acceleration loads
Acceleration loads are are used to simulate the ground motion of a a time-history acceleration acceleration record. CSI Software software assumes complete fixity for all supports, then automatically computes acceleration loads at each node and element. structural object.
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Translational acceleration loads
Translational acceleration loads are taken as the negative product of the product of assembled joint mass and input acceleration.
Please see the CSI Analysis Reference Manual (chapter: Load Cases, section: Acceleration Loads) for greater detail on acceleration loads.
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At any point in a structure, translational acceleration is given by the cross product of the position vector (relative to the origin of rotation) and the acceleration vector. Resultant force is the negative product of this translational acceleration value and the translational mass. For example, RY acceleration would generate MY, FX, and FZ values.
Rotational acceleration loads
Rotational acceleration is calculated independently from rotational inertia. This is done by applying, at the global origin, a unit rotation about the axis considered for the rotational-acceleration computation.
While applying a rotational-acceleration load during time-history analysis, users may specify a coordinate system and an angle from the vertical Z-axis. Rotational acceleration is then applied at the origin of that coordinate system, about the corresponding designated axis. Note that:
- Rotational acceleration is constant through all points in a structure.
- Rotational inertia may induce negative moment values.
Translational acceleration, at any point in a structure, is given by the cross product of the position vector (relative to the origin of rotation) and the acceleration vector. Resultant force is then the negative of the product of this translational-acceleration value and the translational mass. For example, RY acceleration would generate MY, FX, and FZ values.
Reference
For additional information, please see the CSI Analysis Reference Manual (Chapter XVII Load Cases, Acceleration Loads).
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NOTE: It is not possible to display the calculated acceleration loads in a tabular format | ||
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Previous page content:Translational Acceleration LoadsTo apply the acceleration loads, the program assumes that the restrained joints do not move. The applied force at a joint is simply the negative of the assembled mass at a joint times the input acceleration. Rotational Acceleration LoadsRotational inertia is NOT needed for rotational acceleration. A unit rotation is applied about the given axis at the global origin. In time-history cases, you can specify a coordinate system and angle (about Z), and the rotational acceleration will be applied about the corresponding axis in that system at that origin. At any point in the structure, the rotational acceleration is equal to that at the origin, and negative moments will be generated for rotational inertia, if any. At any point in the structure, the translational acceleration is given by the cross product of the position vector from the origin of rotation and the acceleration vector. The negative of this translational acceleration times the translational mass will be the force. The RY acceleration generates MY, FX, and FZ. This is basic mechanics, the conjugate to summing moments at a point from moments and forces distributed throughout the structure. |