Structural Steel Design: Chapter 6 - Compression Members, Exams of Structural Design and Architecture

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STRUCTURAL STEEL DESIGN - CIVE

CHAPTER 8: SYMMETRIC

COMPRESSION MEMBERS

(HSS)

Antoine N. Gergess, PhD, PE, F.ASCE

Professor, University of Balamand

OUTLINE

• Design of Singly Symmetric Sections

• HSS (non-slender and slender)

• W shapes: Fy = 50 ksi, all sections were non slender

Slender

Select an ASTM A500 Grade C rectangular HSS compression member, with a length of 20 ft, to support a dead load of 85 kips and live load of 255 kips in axial compression. The base is fixed and the top is pinned. The solution will be provided using: (1) AISC Manual Tables (2) Calculations using AISC Specification provisions Solution:

1. From AISC Manual Table 2- 4 , the material properties are : ASTM A500 Grade C, rectangular HSS; (^) Fy = 50 ksi; (^) Fu = 62 ksi (see next page)
2. Pu = 1.2 85 kips+ 1.6 255 kips = 510 kips
3. KxLx = KyLy =0.8 x 20ft = 16ft b/t and h/t must satisfy the condition

• Select section with effective length KyLy = 16 ft and Pn Pu = 510 kips from slide
  • Fy = 46ksi HSS12X10X3/
  • Fy = 50ksi; HSS 12x10x5/

Example 3 ( cont’d )

3. From AISC Specification Commentary Table C-A-7.1, for a fixed-pinned

condition, KxLx = KyLy = 0.80. 0.80 20 ft=16.0 ft

4. Enter AISC Manual Table 4-3 for rectangular sections. Try a

HSS12 10 3/8. cPn = 518 kips 510 kips o.k.

h/t b/t

Say we selected HSS12x10x5/16 since Fy=50ksi is larger than table

value of 46 ksi

• b/t = 31.4; h/t = 38.2 33.7 (limit from previous page);

so section is slender. Let us go back to the previous

section as later we will learn how to deal with slender

HSS sections.

Example 3 (cont’d)

Larger between kxLx/rx and kyLy/ry

Example 4

• HSS Slender See next slides for section properties b = 43 0.174 = 7.5 in. h = 66 0.174 = 11.5 in. Length is designated as L Effective length is designated as KL (in steel manual it is designated as Lc )

Section is slender in the short direction b/t Section is slender in the long direction h/t If one of the conditions is not satisfied, then the section is slender

 Length is designated as^ L^
 Effective^ length is designated as^ KL^ (in steel manual it is designated as Lc ) Calculate capacity as before: We need to adjust the stress Fcr to account for slenderness (following slides)