Translational acceleration loads
Acceleration loads are used to simulate the ground motion of a time-history acceleration record. CSI Software assumes complete fixity for all supports, then automatically computes acceleration loads at each node and element. Translational-acceleration loads are taken as the negative of the product of assembled joint mass and input acceleration.
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 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.
Please see the CSI Analysis Reference Manual (chapter: Load Cases, section: Acceleration Loads) for further discussion on acceleration loads.
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 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 designated axis.
Rotational acceleration is constant through all points in a structure.
Rotational inertia may induce negative moment values.
