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Building Design and Construction Handbook - Merritt - Ventech!

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COLD-FORMED STEEL CONSTRUCTION 8.25<br />

where K � effective length factor<br />

L � unbraced length of member, in<br />

r � radius of gyration of full, unreduced cross section, in<br />

E � modulus of elasticity of the steel, ksi<br />

Moreover, angle sections should be designed for the applied axial load P acting<br />

simultaneously with a moment equal to PL/1000 applied about the minor principal<br />

axis <strong>and</strong> causing compression in the tips of the angle legs.<br />

The slenderness ratio KL/r of all compression members preferably should not<br />

exceed 200, except that during construction only, KL/r preferably should not exceed<br />

300.<br />

For treatment of sections that may be subject to torsional or torsional-flexural<br />

buckling, refer to AISI ‘‘Specification for the <strong>Design</strong> of Cold-Formed Steel Structural<br />

Members,’’ American Iron <strong>and</strong> Steel Institute, 1101 17th St., NW, Washington,<br />

DC 20036.<br />

8.14 COMBINED AXIAL AND<br />

BENDING STRESSES<br />

Combined axial <strong>and</strong> bending stresses in cold-formed sections can be h<strong>and</strong>led the<br />

same way as for structural steel. The interaction criterion to be used is given in the<br />

AISI ‘‘Specification for the <strong>Design</strong> of Cold-Formed Structural Members.’’<br />

JOINING OF COLD-FORMED STEEL<br />

Cold-formed members may be assembled into desired shapes or spliced or joined<br />

to other members with any of various types of fasteners. For the purpose, welds,<br />

bolts, <strong>and</strong> screws are most frequently used, but other types, such as rivets, studs,<br />

<strong>and</strong> metal stitching, can also be used.<br />

8.15 WELDING OF COLD-FORMED STEEL<br />

Electric currents are generally used in either of two ways to joint cold-formed steel<br />

components, with electric-arc welding or resistance welding. The former method is<br />

described in Art. 8.16 <strong>and</strong> the latter in Art. 8.17.<br />

Welding offers important advantages to fabricators <strong>and</strong> erectors in joining steel<br />

structural components. Welded joints make possible continuous structures, with<br />

economy <strong>and</strong> speed in fabrication; 100% joint efficiencies are possible.<br />

Conversion to welding of joints initially designed for mechanical fasteners is<br />

poor practice. Joints should be specifically designed for welding, to take full advantage<br />

of possible savings. Important considerations include the following: The<br />

overall assembly should be weldable; welds should be located where notch effects<br />

are minimal; the final appearance should not suffer from unsightly welds; <strong>and</strong> welding<br />

should not be expected to correct poor fit-up.<br />

Steels bearing protective coatings require special consideration. Surfaces precoated<br />

with paint or plastic are damaged by welding. Coatings may adversely affect

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