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Understanding Purlin Distortional Buckling in DIY Projects: Key Parameters and Tests

Dive into the complexities of purlin design with our guide on Distortional Buckling in DIY projects. In this analysis, we explore the key centerline dimensions, material properties, and test results for Z-section purlins, essential for ensuring structural integrity. With specific focus on centerline dimensions and fundamental strength properties (E, G, fy), this resource deciphers the critical specifications outlined in the AISI updates regarding distortional buckling. Stay informed on the implications of these provisions as they relate to the Direct Strength Method and enhance your DIY construction projects.

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Understanding Purlin Distortional Buckling in DIY Projects: Key Parameters and Tests

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  1. Purlin DIY Problem #1 • Find My, Mcrl, Mcrd and Mcre for 72” centerline dimensions h = 7.507 in. b = 1.889 in. d = 0.795 in. r = 0.217 in. t = 0.059 in. properties E = 29500 ksi n = 0.3 G = 11346 ksi fy = 55 ksi

  2. DSM for Purlin DIY Problem #1

  3. Remember Distortional Buckling Gotcha!- comparison of two series of tests Test 8.5Z092 P Local buckling test Distortional buckling test 99% of NAS 83% of NAS Δ Test 8C043 P Local buckling test Distortional buckling test 106% of NAS 90% of NAS Δ

  4. Review DB in AISI Specification • Distortional buckling provisions are integral to the Direct Strength Method of Appendix 1 • The main Specification now has distortional buckling provisions as well, see Ballot 227B 227B Spec. 227B Comm.

  5. Distortional Buckling Commentary • “Testing on 8 and 9.5 in. (203 and 241 mm) deep Z-sections with a thickness between 0.069 (1.75 mm) and 0.118 in. (3.00 mm), through-fastened 12 in. (205 mm) o.c., to a 36 in. (914 mm) wide, 1 in. (25.4 mm) and 1.5 in. (38.1 mm) high steel panels, with up to 6 in. (152 mm) of blanket insulation between the panel and the Z-section, results in a kf between 0.15 to 0.44 kip-in./rad./in. (0.667 to 1.96 kN-mm/rad./mm) (MRI 1981).”

  6. Purlin DIY Problem #1 with spring • Find My, Mcrl, Mcrd and Mcre for 72” with kf=0.15 kip-in/rad/in centerline dimensions h = 7.507 in. b = 1.889 in. d = 0.795 in. r = 0.217 in. t = 0.059 in. properties E = 29500 ksi n = 0.3 G = 11346 ksi fy = 55 ksi

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