Example 321

Relative Column Brace Design

A typical tension-only X-brace must stabilize three bents. Each bent carries a total factored load of 600 kip (125 + 300 + 175). Assume the floor acts as a rigid diaphragm and all Do = 0.002L and all columns are W14 x 53 (Ag = 15.6in.2).

125 k

300 k

175 k

125 k

300 k

175 k

Bracing shear force: Bracing shear stiffness:

^Pu =(3 bents)(125 + 300 + 175) = 1800 kip Pbr = 0.004(1800) = 7.2 kip

Design recommendations assume brace shear force and stiffness are perpendicular to column. Therefore, for an inclined threaded rod (A36 steel):

Strength: Stiffness:

Consider effects of shortening 300 k

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