RISA 3D 7.0 Code checking discprepancy

[cessna98j]

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.

 

[haynewp]

Then SAP agrees with STRUDL for the 3rd edition check (STRUDL doesn't have 13th check yet that I know of). And (1.5My/1.6My)*0.83=0.778, so it is using the higher limit in both cases (not the 1.0My).

 

[cessna98j]

WillisV - I just had a 10K dead load and excluded self weight. I used a load factor of 1.0 for the DL in my load case to keep the numbers nice.

Haynewp - my hand calcs yielded the same, and now I can see how RISA obtained the value that it did.

Thanks for all the replies, its interesting to get comparisons from other programs as well and see how they interpret the code differently for things such as this.