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A Beginner's Guide to the Steel Construction Manual, 16th ed. Chapter 7 - Concentrically Loaded Compression Members © 2006, 2008, 2011, 2017, 2023 T. Bartlett Quimby |
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Section 7.2 Slenderness Limit State Last Revised: 06/24/2023 The slenderness limit state is found in SCM E2. In actuality, slenderness is not a firm limit state. It is a suggestion, much like the slenderness limit state discussed in the tension member chapter. Slender members are difficult to handle, in addition to being weak under compressive loads. This limit state, if adhered to, will result in the selection of members that are easier to handle during fabrication and erection. The Limit State The limit state simply recommends at the slenderness ratio, Lc/r, not exceed 200 within a structure nor exceed 300 for the member as fabricated. This is not a requirement. The user note in SCM E2 implies that the Lc/r is the maximum Lc/r for the member--this can either be in the member's final location in a structure or during construction. Mathematically these suggestions are stated as:
It is good to note that members with slenderness ratios as high as 200 have little compressive strength. This will become apparent as member strength is computed in the following sections. Consequently, it is uncommon to find such slender compression members in a structure as they rarely have the needed strength to support the applied loads. The design process will lead to columns with much smaller values of Lc/r than those recommended in this section. Also, members fabricated with a slenderness ratio of 300 are difficult to handle without damage, so it is rare to see members having slenderness ratios approaching the recommended maximum slenderness ratio. SCM E2 states that the effective length, Lc, using in this section "may be determined using an effective length factor, K, or a buckling analysis". The effective length factor, K, is determined using the resources in Appendix 7. If this section is being used to consider the stiffness during construction handling, then it is appropriate to use K=1 in most cases. |