The Ontario Building Code | Direction of Loading
220.127.116.11. Direction of Loading
(1) Earthquake forces shall be assumed to act in any horizontal direction, except that the following shall be considered to provide adequate design force levels in the structure:
(a) where components of the SFRS are oriented along a set of orthogonal axes, independent analyses about each of the principal axes of the structure shall be performed,
(b) where the components of the SFRS are not oriented along a set of orthogonal axes and IEFaSa(0.2) is less than 0.35, independent analyses about any two orthogonal axes is permitted, or
(c) where the components of the SFRS are not oriented along a set of orthogonal axes and IEFaSa(0.2) is equal to or greater than 0.35, analysis of the structure independently in any two orthogonal directions for 100% of the prescribed earthquake loads applied in one direction plus 30% of the prescribed earthquake loads in the perpendicular direction, with the combination requiring the greater element strength being used in the design.