Determining the location of overturning axes

Lateral forces generated from an earthquake or other sources, when applied to equipment cabinets, produce an overturning moment that acts on the base of the cabinet. This moment causes the cabinet to overturn about an axis called overturning axis (O.T. Axis). GIP, Revision 2 and the EPRI reports constituting the basis for GIP suggest that O.T. Axis is located at the outer edge or far side bolt centerline for equipment with rigid base. For flexible equipment such as electrical cabinets, the above references suggest that the O.T. Axis is close to the equipment base centerline. It is a common design practice to assume that O.T. Axis is located at the centerline of the equipment base plan. However, this assumption is only valid for equipment with a relatively flexible base framing. The existing guidelines and current state-of-practice do not provide an accurate direction for locating the O.T. Axis. In this study, a series of electrical cabinets with more commonly used base framing-anchor bolt combinations are evaluated to develop guidelines for locating the O.T. Axis of the equipment cabinets under application of lateral loads