Example 4.5 A compression member is subjected to service loads of 165 kips dead load and 535 kips of live load. The member is 26 ft. long and pinned at each end. Use A992 (50 ksi) steel and select a W shape Solution Calculate the factored design load Pu Pu = 1.2 PD + 1.6 PL = 1.2 x 165 + 1.6 x 535 = 1054 kips Select a W shape from the AISC manual Tables For KyLy = 26 ft. and required strength = 1054 kips Select W14 x 145 from page 4-15. It has = 1230 kips cPn Select W12 x 170 from page 4-18. It has = 1130 kips cPn No W10 will work. See Page 4-21 W14 x 145 is the lightest. Note that column sections are usually W12 or W14. Usually sections bigger than W14 are usually not used as columns. 4.8 DESIGN OF SINGLY SYMMETRIC CROSS-SECTIONS So far, we have been talking about doubly symmetric wide-flange (I-shaped) sections and channel sections. These rolled shapes always fail by buckling. flexural Singly symmetric (Tees and double angle) sections fail either by buckling about the flexural axis of non-symmetry or by buckling about the axis of symmetry and the flexural-torsional longitudinal axis. Flexural torsional buckling Flexural buckling Figure 6(a). Figure 6(b).
Example 4.5 A compression member is subjected to service loads of 165 kips dead load and 535 kips of live load. The member is 26 ft. long and pinned at each end. Use A992 (50 ksi) steel and select a W shape Solution Calculate the factored design load Pu Pu = 1.2 PD + 1.6 PL = 1.2 x 165 + 1.6 x 535 = 1054 kips Select a W shape from the AISC manual Tables For KyLy = 26 ft. and required strength = 1054 kips Select W14 x 145 from page 4-15. It has cPn = 1230 kips Select W12 x 170 from page 4-18. It has cPn = 1130 kips No W10 will work. See Page 4-21 W14 x 145 is the lightest. Note that column sections are usually W12 or W14. Usually sections bigger than W14 are usually not used as columns. 4.8 DESIGN OF SINGLY SYMMETRIC CROSS-SECTIONS So far, we have been talking about doubly symmetric wide-flange (I-shaped) sections and channel sections. These rolled shapes always fail by flexural buckling. Singly symmetric (Tees and double angle) sections fail either by flexural buckling about the axis of non-symmetry or by flexural-torsional buckling about the axis of symmetry and the longitudinal axis. Figure 6(a). Flexural torsional buckling Figure 6(b). Flexural buckling
CE470-Ch-4-Compression-Design-K=1.docx