Ray Castillo/Gordon-Fiano

Unlike a shear-wall assembly, where the anchor points between the wall base and the foundation are assumed to pick up an overturning load on the shear wall, moment frames do their work in the upper corners of the frame. There they resist the "moment"—the force of bending or rotation—with a rigid connection at the joint between the column and beam, rather than relying on the joint between the base of the column and the foundation it rests on.

In terms of overturning, a moment frame is analyzed like a single large shape. Its two narrow columns aren't considered to be overturning independently; instead, the entire frame around a garage door or large window may be trying to overturn as a 9- by 20-foot unit. If the weight of an upper story is resting on the header beam, the uplift on...

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