The program has built-in ground acceleration loads UX, UY, UZ, RX, RY, and RZ. The UX, UY, and UZ loads correspond to unit translational acceleration of the ground in the global X, Y, and Z directions, respectively. The RX, RY, and RZ loads correspond to unit rotational acceleration about the global X, Y, and Z directions, respectively. Typically for any load case where loads can be applied from load patterns, ground acceleration loads also can be applied.
Static, modal, and buckling load cases permit only global acceleration loads, UX, UY, UZ, RX, RY, and RZ.
Response-spectrum and time-history load cases permit application of ground acceleration in a local coordinate system. Specify a previously defined coordinate system name, and an angle of rotation about the Z axis. The acceleration load names are U1, U2, U3, R1, R2, and R3:
U3 is always the same as UZ in the specified coordinate system.
U1 and U2 are rotated from UX and UY in the specified coordinate system by the given angle.
Tip: By default, the global coordinate system is used and the angle is zero, so that U1, U2, U3, R1, R2, and R3 are the same as UX, UY, UZ, RX, RY, and RZ.
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The Linear Static, Nonlinear Static, Modal, Linear Modal History, Linear Direct Integration History, Response Spectrum, Nonlinear Modal History, Nonlinear Direct Integration History, Buckling, Steady State, and Power Spectral Density forms have options to apply acceleration loads. |