## 243

F 29,000

Fv V 50

Since the width-thickness ratios of all component shapes do not exceed the limiting width-thickness ratio for local buckling, local buckling is not a concern.

Check for flexural buckling about the major (x-x) axis: Since the built-up section is doubly symmetric, the governing buckling mode will be flexural buckling regardless of the axes. Flexural buckling will occur about the major axis if the modified slenderness ratio (KL/r)m about the major axis exceeds (KL/r)y. Therefore, as long as (KL/r)m is less than (KL/r)y, buckling will occur about the minor axis and flexural buckling about the major axis will not be controlled. In order to arrive at an optimal design, we shall p determine the longitudinal fastener spacing, a, such that the modified slenderness ratio (KL/r)m about the major axis will be equal to (KL/r)y. That is, we shall solve for a from the equation

KL r

In the above equation, (KL/r)x is the slenderness ratio about the major axis of the built-up section, r{ is the least radius of gyration of the component shapes, which in this case is the cover plate.

Substituting (KL/r)x = 21.7, r{ = rcoverplate = V(IMLverplate = VKf)2/12]= 0.108 into the above equation, we obtain a = 7.62 in. Since (KL) = 20 ft, we shall use a = 6 in. for the longitudinal spacing of the fasteners.

Check for component element buckling between adjacent fasteners:

Ka 1x6

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