risa 3d 7.0 code checking discprepancy

huangyhg

risa 3d 7.0 code checking discprepancy
so we just received the latest version of risa 3d, v7.0 which now includes code checking from the aisc 13th.  i thought i would do some code check comparing and noticed a pretty substantial difference between the lrfd 3rd edition and aisc 13th (lrfd) code check when looking at wt sections in flexure.  for example, a simply supported wt8x20 unbraced, with a 10k load at mid-span yields a unity check of around 1.43 based on lrfd 3rd ed. code in risa.  however, by just changing the code to aisc 13th (lrfd), the code check drops by nearly half to 0.7.  the thing is, both code checks reference the exact same equation in their respective references (h1-1b, and hand calcs tend to agree more with the aisc 13th (lrfd) code check, but i would think risa would show exactly the same code check because the equations are the same for singly symmetric members in both books.  seeing as how hand calcs tend to agree more with the aisc 13th ed. code check, it looks like the lrfd 3rd code checking for wt sections was perhaps not done correctly in the previous versions of risa as well.  has anyone else had a chance to look at risa 7.0, or can somebody confirm?  was thinking maybe i should send an email to risa to let them know of the situation.
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definitely send them an email.  this is the sort of thing that we as engineers should be very proactive about.  the use (and mis-use) of software can be minimized if we always notify our software vendors of suspected problems right away.  we've received 7.0 but not installed it yet so i can't check your numbers myself with 7.0.
definitely send an e-mail.  
great job verifying with a hand calc!  it's scary how many people don't do that.  if the 3rd ed. implementation was wrong, that's really scary considering how long ago risa added that.
i know of one multi-zillion dollar fix that was required because an engineer did not check what another program was doing with wts.  the program's wt implementation was flat wrong and the trusses started to collapse when they started sitting the precast on it.  problem was that there were dozens of these trusses already up.
i agree with the above.  send the email (and tell us what they say).  and assuming your hand calc shakes out correctly, kudos on the catch!
i really don't mean to hijack this thread, but 271828, do you have a reference, case study, or any further information about the failure you mentioned?  i only asked because our office is currently designing a staggered truss building with wt sections as the diaphragm chords.  we're detailing the precast plank to brace the trusses during construction, but i would be interested in reading more about that issue.
i wish they had a personal message feature on these forums, but i guess that would attract recruiters.  ah well...
jkstruct, i can't say enough to id the firm or project, but i can say is that it had to do with checking the wts for bending.  it was a large stadium and had the same trusses all the way around.  at some point in the design, a walkway was added that chopped out part of the truss and made a vierendeel panel.  
this was about 6 years ago, so that software isn't being used nowadays.  it wasn't a spec. problem.  the software was just plain wrong, spitting out phimn that weren't even close.  i'm sure it's been fixed by now.
it comes down to the age old issue:  the design engineer was in a big hurry like we all are and didn't verify the results.  i've done that as i'm sure most here have, but he was unlucky.
i also wish we had a pm feature.
well i emailed risa and here is there response:
"the difference is likely related to the different ways that the two codes handle slender elements.  it looks to me that the 13th edition doesn’t care about web slenderness for bending.  in the 3rd edition, chapter f specifically does not apply to   
i would've hoped that risa would know why the answers are different not use language like "likely related"--oh well, i guess that's too much to ask.
the commentary to f9 talks about this stuff.
i don't have my 3rd ed. here, so i can't look at the difference between the two formulations.
what is the length of the wt?
the length that i used was 10 feet, wt8x20.
also, the wt is oriented such that the loading is in the plane of symmetry, and the stem of the tee is in tension.
looks as though risa used a "conservative" interpretation of the 3rd edition in version 6.  the opening paragraph of  (3rd ed.)chapter "f" reads "for