In Advance Design the definition of a quake is made on two main orthogonal directions but sometimes it is necessary to load a structure from seismic loads acting on different directions.
The seismic load acting on any direction is defined by creating load combinations each having the two main seismic load cases acting concomitant reduced with a calculated coefficient corresponding to the desired direction.
For example a seismic load case acting at the +45°, -45°, +135° and -135° angles from the main axis x-x, the combination coefficients will be calculated by decomposing the vector equal with the value 1 by the two main directions.
By modifying the load case coefficients in the combination, we can simulate a seismic load case acting on any direction.