16

1: Node number 1: Element number

FIGURE 5.42 Structural modeling of the eight-story frame.

Step 5: Check of serviceability. The lateral drift at the roof level by the wind load (1.0W) is 5.37 in. and the drift ratio is 1/198, which does not satisfy the drift limit of 1/400. When W40 x 174andW24 x 76are used for column and beam members, respectively, the lateral drift is reduced to 2.64 in. and the drift ratio is 1/402, which satisfies the limit 1/400. The design of this frame is thus governed by serviceability rather than strength.

5.6.2.2 Comparison of Results

The sizes predicted by the proposed methods are W33 x 130 columns and W21 x 50 beams. They do not, however, meet serviceability conditions, and must therefore be increased to W40 x 174 and W24 x 76 members. The LRFD method results in the same (W40 x 174) column but a larger (W27 x 84) beam (Figure 5.43).

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