Section 8.2.2.1.1 of ATC-40 defines a kappa factor, k, which modifies the calculated area of the hysteresis loops to account for pinching of the loops depending on the structural behavior of the building. Structural Behavior Types A, B, and C are described, and curves for the k factor are provided (see Figure 8-15 in ATC-40). The curves describing the k factor are trilinear, with the first segment having a constant k value, the second segment having a linearly varying k value, and the third segment having a constant k value. Thus the k factor curves can be described with just two points, those at the beginning and end of the second segment. The point at the beginning of the second segment is designated Point 1, and the point at the end is Point 2.