Translational Acceleration Loads

To apply the acceleration loads, the program assumes that the restrained joints do not move. The applied force at a joint is simply assembled mass at a joint times the input acceleration. Unfortunately, it is not possible to display the calculated acceleration loads in a tabular format.

Rotational Acceleration Loads

Rotational 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.