MechStruct1
Structural
- Sep 8, 2010
- 15
Hi all!
I am trying to qualify some existing Unistrut P1000 trapeze members for seismic loads. Local buckling is not expected because of the pipes strapped to it every few inches. However, the ASD moment capacity given by Unistrut in their catalog is 5070 in*lbs (422.5 ft*lbs). They also state that the safety factors to yield and ultimate are 1.67 and 2.0, respectively, for flexure.
1) Is it correct to take their listed ASD capacity value and factor it by 2.0 (their listed safety factor to ultimate), then multiply by the LRFD phi factor of 0.9 for flexure to arrive at an LRFD design flexural strength? See image below:
2) I was made aware that (if the above statement is correct) this would only be true for a compact section. I did a compactness check (AISC 14th Ed. Table B4.1b) with a simple channel shape (not including the turned in stiffening lips of the P1000) and found that the section is noncompact. See image below:
3) In order to try to show that the section is compact, I used AISI S100's Appendix 1, Sections 1.1.a and 1.2.2.a (using 1.2.2.a.1) to calculate an effective width of the P1000 section with the rounded over lip. However, I am coming up with a smaller effective width “b” that I started with without the lip! The part I am not super clear on is the calculation of the stresses (f, f.1, and f.2) in the compression element. See attached Mathcad file (Heading in [highlight #3465A4]BLUE[/highlight]) with helpful screenshots on the right pages.
Thank you for any insight you might be able to give!!!
Tags: AISI S100, Effective Width, Unistrut, P1000, Unstiffened Elements, Effective Width of Elements
I am trying to qualify some existing Unistrut P1000 trapeze members for seismic loads. Local buckling is not expected because of the pipes strapped to it every few inches. However, the ASD moment capacity given by Unistrut in their catalog is 5070 in*lbs (422.5 ft*lbs). They also state that the safety factors to yield and ultimate are 1.67 and 2.0, respectively, for flexure.
1) Is it correct to take their listed ASD capacity value and factor it by 2.0 (their listed safety factor to ultimate), then multiply by the LRFD phi factor of 0.9 for flexure to arrive at an LRFD design flexural strength? See image below:
2) I was made aware that (if the above statement is correct) this would only be true for a compact section. I did a compactness check (AISC 14th Ed. Table B4.1b) with a simple channel shape (not including the turned in stiffening lips of the P1000) and found that the section is noncompact. See image below:
3) In order to try to show that the section is compact, I used AISI S100's Appendix 1, Sections 1.1.a and 1.2.2.a (using 1.2.2.a.1) to calculate an effective width of the P1000 section with the rounded over lip. However, I am coming up with a smaller effective width “b” that I started with without the lip! The part I am not super clear on is the calculation of the stresses (f, f.1, and f.2) in the compression element. See attached Mathcad file (Heading in [highlight #3465A4]BLUE[/highlight]) with helpful screenshots on the right pages.
Thank you for any insight you might be able to give!!!
Tags: AISI S100, Effective Width, Unistrut, P1000, Unstiffened Elements, Effective Width of Elements
