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4.1. AISC Specification Requirements

4.1.1. Can the AISC Specification be used to design structural shapes not listed in Part 1 of the 13th Steel Construction Manual?

Yes. AISC's Steel Manual is written based upon the AISC Specification for Structural Steel Buildings and provides design aids and charts for commonly used structural shapes: those listed in ASTM A6/A6M as well as hollow structural Sections [HSS] (square, rectangular, and round). This coverage is not intended to exclude the use of other shapes that may be available. Other shapes and combinations thereof may be designed and used within the requirements of the AISC Specification.

4.1.2. It is indicated in the AISC Specification Section D1 that the slenderness ratio of a tension member should preferably not exceed 300. Why? Is this requirement strength related?

From the AISC Specification Commentary Section D1, Users Note, this recommended limit is "based on professional judgment and practical considerations of economics, ease of handling, and care required to minimize inadvertent damage during fabrication, transport and erection." It is further indicated that this requirement is not strength related.

Essentially, this rule also ensures that a non-pretensioned structural brace will be stiff enough that significant lateral deflection of the structure will not be required to activate the strength of the brace. As such, this requirement does not pertain to rod bracing, cable bracing and other light bracing systems that are fabricated and installed with draw to activate the brace.

4.1.3. What is the nominal bending moment for weak-axis bending of a channel with compact flanges?

Channels in weak-axis bending with compact flanges can be designed for flexural yielding. With thick, stocky flanges and thicker webs, flange- and web-local buckling do not control. 

AISC Specification Section F6 addresses I-Shaped Members and Channels Bent about Their Minor Axis. F6.2(a) states: “For sections with compact flanges, the limit state of flange local buckling does not apply.”