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torsion check in STAAD Pro using AISC 360-10

torsion check in STAAD Pro using AISC 360-10

torsion check in STAAD Pro using AISC 360-10

(OP)
hi

i have tried using the AISC 360-10 code for the torsion check for a simply supported beam, in STAAD Pro - std file attached.

while using the pipe section for the analysis, stress ratio is increasing for the pipe size of 102mmx25 thk to 254mmx25 thk

how the stress ratio is increase for the higher pipe size???

i have checked the track 3.0 of the member for the lower pipe size it is calculating the normal stress as 11.78ksi but for the higher pipe size i.e. 254x25mm thk it is coming 115.92ksi.

As per AISC design guide 9 there will not be any normal stress for pipe section. so why it is calculating the normal stress???

RE: torsion check in STAAD Pro using AISC 360-10

as i recall the shear stress resulted from torsion is calculated form this equation ( T*r/J) so if the radius of the section increased the shear stress from the torsion will increase also (of course the polar moment of inertial will increase as will but i guess in your case the radius effect is larger) .

i haven't looked into your staad model i am just suggesting , i hope it helped.



“If you don't build your dream someone will hire you to help build theirs.”

Tony A. Gaskins Jr.

RE: torsion check in STAAD Pro using AISC 360-10

I don't think STAAD supports torsion as per AISC 360.....I think they still run with the 9th edition on that. (At least the version I have does.) As such, I couldn't get your model to run. I changed the ending to this:

*
LOAD COMB 2 COMBINATION LOAD CASE 2
1 1.0
PERFORM ANALYSIS PRINT ALL
LOAD LIST 2
PARAMETER 1
CODE AISC
*
TORSION 2 MEMB 1
TRACK 2 MEMB 1
*
CHECK CODE ALL
*
STEEL TAKE OFF ALL
*
FINISH

I assume you are working in ASD, so my load factor was 1.0. Running it on my end I got a stress ratio of 0.49.

RE: torsion check in STAAD Pro using AISC 360-10

I don't have Stad so I'm a bit in the dark here. However, Malikasal's theory sounds plausible to me. Check this out: Link

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: torsion check in STAAD Pro using AISC 360-10

(OP)
thanks for your reply

if you go for higher pipe size i found that increase in r is less than J, so if manually calculate it is
obvious that the torsional capacity of the pipe size 168.3x6.3 is higher than 101.6x6.3,

but in staad the shear stress is calculated correctly but the there is a normal stress also coming for closed section.

which is not correct as per aisc design guide 9

regards

RE: torsion check in STAAD Pro using AISC 360-10

Quote:

but in staad the shear stress is calculated correctly but the there is a normal stress also coming for closed section.

which is not correct as per aisc design guide 9

I'm not getting any "normal" (I.e. compressive/tensile) stresses on my end that don't match what hand calculations show that should be there for the flexural stresses. Keep in mind, you've got a 15 kip load mid-span, so you will have compressive/tensile stresses from bending (which must be combined with warping stresses [if any; as you say: there should be none for a closed section]).

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