dear staad master.
i'm new member in here. i love this forum because i can find the answers about lots of my own problem with staad besides reading technical manual reference from staad.
now i'm working with (maybe) the latest patch released from staad pro v8i series 4 20.07.09.31. and i'm using AISC 360-10 code because of client requirement for my project.
then i contact to IT to upgrade the staad to series 4 because staad has the 360-10 code.
unfortunately. i have some questions regarding AISC 360-10 code.
question no 1.
how to change base staad unit ?
i'm in Indonesia, we use Metric instead of English. I change the base-units in configuration to Metric, but the output still using English-units.
i change the configuration file from staadpro20070.ini still doesn't give any change. i think the AISC 360-10 code output doesn't give the metric output.
when i check using different code (9th edition) the output give me metric unit.
please, bentley staad creator, could you fix this ?
question no 2.
in the history version of staad series 4 (http://communities.bentley.com/products/structural/structural_analysis___design/b/analysis_and_design_blog/archive/2012/12/05/staad-pro-v8i-selectseries-4-patch-release.aspx )
it is noted
A) 04 The AISC 360-10 steel design module has been enhanced with thereintroduction of the MAIN and TMAIN parameters. Setting either to 1.0 willbypass any slenderness checks."
in example "STAADPro_V8i_AISC_13th_Ed_Design_Example_Verification.pdf" , the input shows :
and the output :
in my staad, when i set MAIN or TMAIN to 1.0, the input
and the result shows :
so the staad didn't bypassed the slenderness check ??
question no 3 :
3. what is the value of the slenderness ratio of : compression member and tension member ?
based on my knowledge, for compression member is 200, and for tension is 300.
the staad seems inconsistent for "MAIN" command for 360-10 code.
in some cases, the kL/r is exceed and give me FAIL for slender member when i'm using the 9th edition code, or 360-05.
but in 360-10, staad give me PASS.
what should i do ?
Presently the Staad reports the design result as per AISC 360-100 in e the English Unit System only . The metric system will be introduced in the upcoming releases .
Question 3 :
From the screenshot it seems, that the FX is reported for LC 5013 and the slenderness check is done for LC 51.
Can you kindly send us the model.
thank you for answering question 1.
for question 3.
i can't share the staad file due to company regulation. i'm so sorry.
but i can show you my study staad for stair tower. this staad represent my problems.
i check using AISC 360-05, staad says error due to slenderness exceeds. in 360-10. staad doesn't give any error message.
for my comparison using beam no 410.
using 360-05 code, staad says FAIL (left image), and PASS in the right image (360-10 code). the kL/r value are same. but the ratio is totally different. why ?
in the left image, i think the staad is correct, because the compression member allowable slenderness is 200. if the kL/r exceed or over 200 ,the member is FAIL.
but in the right image, 360-10 code says the member is a tension member. which mean the slenderness ratio is "should be" 300. right ? so it PASSED.
however, in the output result i will show you in below image.
staad pro using different load case for strength check and slenderness check. am i right ?
above explanation : critical ratio, and biggest force happens due to load case 105 and the member experiencing tension. but for slenderness check, staad (using 360-10 code) check using LC 101. the actual slenderness is 228 which over than the allowable (200 for compression). but staad doesn't say this a problem. it is PASS(ed).
i do checking via Post-Process to earn the beam force. it is true, that in the LC 105 the member is tension. and the LC 101 makes the beam compress.
but, why staad using the LC 101 instead of LC 105 for slenderness check ?
what is wrong in here ?
This is regarding question no. 3
A change has been made in the ratio reporting for AISC 360-10 in the context of Slenderness .
If a member is passing in both the Slenderness and Stress, then only the stress ratio would be reported even if the former ratio is higher than that of latter.
Now, by default Staad considers the ratio with respect to unity . That means if the slenderness and stress ratios are both less than unity then the slenderness ratio would not be reported . But in your model , the maximum ratio has been specified as 1.33 ( by the parameter RATIO 1.33) , that means both the Slender Ratio (228/200) =1.14 and STRESS ratios are less than 1.33 and hence the STRESS ratio is only reported , which is not the case of AISC 360-05 . In AISC 360-05 , Staad could report the slenderness ratio critical even if it is passed .
If you replace the ratio parameter (RATIO 1.33 with RATIO 1) in case of AISC 360-10 , then you would notice that the critical ratio is being reported against slenderness as the member is failing in Slenderness
thank you for your great explanation Mr. Biswa.
now i understand some mysteries in staad 360-10 code.
so, do you mean the ratio for slenderness is also increase due to "RATIO" command which is in the AISC 360-05 the RATIO command only check for the stress.
why staad don't make it same like 360-05's report ?
the actual condition of the member, is actually slender. but AISC 360-10 says OK.
what will happen, if i just "blind" to this matter, and i follow the STAAD says OK, otherwise, actual member is slender member.
so, my step will be :
1. use RATIO of 1.0 for slenderness check, then
2. use RATIO of 1.33 for my strength design.
until i get the optimum members, i need to run twice to achieve that.
There is a change in AISC 360-10 as comapred to AISC 360-05 in Slenderness ratio consideration
Yes , you are correct , AISC 360-05 compares the Slenderness Ratio only with rspective to unity irrespective of any value specified by the RATIO parameter .
You would be notified once I have more explanation from Develoment team on this .
thank you Mr. Biswa for your help.
i really waiting for your further reply.
because this new code seems different for us, moreover the units still in English not Metric. :(
how about question number 2 ?
i can't bypass the slenderness check when i entered
MAIN 1.0 ALL
the output still read the allowable slenderness.
I could see that the MAIN parameter deos work fine in your model .
Please find attached the modified model .
another question.for allowable slenderness of a member, which is more decisive, compression member or tension ?
i think compression member is more decisive because the allowable slenderness is 200 (tension 300).
my intention is, when a member experiencing all compress in all load case, so the member is a compression member which allowable slenderness is 200.
and vice versa, if a member experiencing all tension in all load case, so the member is a tension member which allowable slenderness is 300.
but how about if a member experiencing compress and tension in all load case ?
in my staad 2010, i check the member 509 experience the compress and tension.
tension for load comb 101 to 104 and 106. compression for load comb 105.
but in output report, the staad consider the slenderness by using load 101 so the allowable is 300.
here's my parameter
PARAMETER 2CODE AISC UNIFIED 2005METHOD ASDTRACK 2 ALLRATIO 1 ALLMAIN 200 ALLLOAD LIST 101 TO 106*LOAD LIST 105CHECK CODE MEMB 509FINISH
when i used AISC 360-05 code, the staad contain error. due to slenderness (FAIL).
so in my opinion, for 360-05 code, the logic will be check the slenderness first, and then the ratio. if slenderness is exceed, and then staad give us ERROR. if slenderness is ok, then staad will check the strength.
but in 360-10 code, the slenderness is checked using the first load case even it is tension or compress (?) instead of the load case which make the member compressed and the output is just like the mention above (only shows the stress ratio).
i do try check the member only use the load list 105 (compression) and the staad give us correct answer.
SLENDERNESS, AND COMPRESSION, AND ALLOWABLE ARE CORRECT.
still i don't get it.....:(
There is no inconsistency.
To bypass slenderness check, you need to add the MAIN command before the CHECK CODE command. Only then the MAIN command will be effective.