Figure 2.28. Vertical geometric irregularity. Vertical geometric irregularity exists if the horizontal dimension of the lateral-force-resisting system is more than 130% of that in the adjacent story: 1.3b < B. For example, the width of frame at level 6 = 160 ft, the width of frame at level 7 = 100 ft. 160 ft > 1.3 x 100. Therefore, vertical geometric irregularity exists.

Figure 2.29. In-plane discontinuity; type-4 irregularity. A type 4-irregularity exists when there is an in-plane offset of the lateral system greater than the width of the system. L > l

Assume L = 60 ft and l = 30 ft. Then the left side of upper brace is offset 60 ft from the left side of lower brace, greater than the 30 ft, the width of the offset brace. Therefore, a type-4 irregularity exists.

Figure 2.30. Discontinuity in capacity (weak story); story strength at levels 4 and 3. A weak story condition exists when the story strength is less than 80% of that of the story above:

For a moment frame, compare the strength of column shears in the two stories. For shear walls, compare the smaller of nominal shear strength Vn or Vm, the shear strength corresponding to the nominal flexural strength.

Figure 2.31. Torsional irregularity. Torsional irregularity exists when dmax, the maximum story drift at a corner including accidental torsion, is more than 1.2 times the average of the drifts at the corresponding corners.
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