BadgerPE
Structural
- Jan 27, 2010
- 500
Hey all,
When checking a 2x6 purlin in RISA 3-D against my hand calcs, I noticed that I get significantly more capacity out of the member in 3-D than I do by hand. I have determined this difference to be associated with the effective span length le. Based upon Table 3.3.3 in the 2005 NDS, the effective length for a simply supported bending member follows one of the two equations:
lu/d<7, le=2.06lu
lu/d>or=7 le=1.63*lu+3*d
I get a slenderness ratio, RB, of 21.7 when calculating by hand and 16.25 when using RISA. This effects my result significantly as the purlin is about 7% understressed using RISA as opposed to about 15% overstressed when using my hand calc. If I insert the RB value of 16.25 into my spreadsheet, I get the same result as RISA.
Has anyone else run into this issue? Am I doing something wrong by using Table 3.3.3? Any help would be greatly appreciated.
When checking a 2x6 purlin in RISA 3-D against my hand calcs, I noticed that I get significantly more capacity out of the member in 3-D than I do by hand. I have determined this difference to be associated with the effective span length le. Based upon Table 3.3.3 in the 2005 NDS, the effective length for a simply supported bending member follows one of the two equations:
lu/d<7, le=2.06lu
lu/d>or=7 le=1.63*lu+3*d
I get a slenderness ratio, RB, of 21.7 when calculating by hand and 16.25 when using RISA. This effects my result significantly as the purlin is about 7% understressed using RISA as opposed to about 15% overstressed when using my hand calc. If I insert the RB value of 16.25 into my spreadsheet, I get the same result as RISA.
Has anyone else run into this issue? Am I doing something wrong by using Table 3.3.3? Any help would be greatly appreciated.
