load envelopes and serviceability and strength checks

Hi

I have assigned some load combinations(101 to 114) as serviceability load cases , and some (201 to 236) as strength load cases in load envelopes.

after that I have mentioned LOAD LIST ENVELOPE 1 2 before parameter 1. so now staad should perform serviceability checks for load combination 101 to 114  and strength checks for 201 to 236.

But when I am going to post processing > unity checks , it is showing deflection check is critical for load cases 201 to 236 .

please have a look at staad file and suggest corrections

.M703-IA-P0.std  

Parents
  • Please refer to the attached modified model. Please note that Envelop 1 is created for serviceability check and envelop 2 is created for strength check.. Just before PARAMETER 1, LOAD LIST ENVELOPE 1  is used and after the parameter lists CHECK code command is used like DFF etc.  It will tell the program to go for deflection checking and the output contains deflection checking results. Similarly, before PARAMETER 2, LOAD LIST ENVELOPE  2 is used and it tells the program to go for strength checking.

    0602.M703-IA-P0.std



  • Hi

    I have reviewed staad model modified by you.

    If we do like this then in post processing >unity check staad shows results only for parameter mentioned later i.e. parameter 2 (strength check).

    but if we mention parameter 1 later (deflection check)as in the case of model attached with this comment by me, than in post processing >unity check staad shows results only for deflection checks.

    That means staad is taking parameter which is mentioned later as critical , whereas what staad should have done is, checked utilisation ratios for both parameters and than should have mentioned ratio which is critical out of this two in

    post processing >unity check.

    please review model sent by me.

    this problem is there in staad since many year , please have a look at the conversation with  and  in below link

     

    communities.bentley.com/.../92737

    communities.bentley.com/.../85977

    4760.0602.M703-IA-P0.std

  • The deflection check which is a serviceability limit state is done for the un-factored load combination and the strength check for the factored load combination.
    To do this, you need to define a new load combination without factoring the primary load cases for the deflection check (serviceability check).

    The alternate way to get the design result and deflection check (un-factored load) check  is by creating two load combinations.

    All you need to do is to use the LOAD LIST command in two different parameters. One for Design with factored load combination and another with un-factored load combination for the deflection check .

    For example

    The load case A to load case B are Primary cases.

    And the Load combinations are as follow.

    Load Combination C = 1.5 ( L/C A + L/C B)....(Factored), Load Combination D = (L/C A + L/C B) ............(Unfactored)




    LOAD LIST C
    PARAMETER 1
    CODE AISC
    BEAM 1 ALL Factored
    RATIO 1 ALL
    TRACK 1 ALL
    CHECK CODE ALL


    LOAD LIST D

    PARAMETER 2

    DFF 200 MEMB x y z..... Unfactored
    DJ1 4 MEMB x y z.....
    DJ2 5 MEMB x y z.....
    CHECK CODE ALL

    Although in the post-processing mode, you can see the utilization ratio of only the last PARAMETER block, but in the output file, you can see the unity ratios of both the individual parameters.



  • Thanks
    you have cleared some things.
    but I think staad developers should look in to this matter and programme it in such a way that in post processing it shows utilisation ratios for critical case out of serviceability and strength , instead of showing results for just last parameter block.
  • I ran the model M703-IA-P0.std that you attached when you initiated the discussion on this thread on Monday, Sept 14, 2015.

    We agree that for those members for which deflection governs, like 7, 9, 10, 11, 14, etc., an incorrect value is listed for the L/C number in the table that appears on the right side of the screen in the Beam-Forces page of the post-processing mode. Fortunately, this appears to be just a reporting error. You can find the correct value of the L/C for those members by viewing the steel design output in the ANL file. See the screenshot below that shows the result for member 7.

    We will get this corrected ASAP.



  • Hi
    please first clear weather I have to mention LOAD LIST ENV 1 and LOAD LIST ENV 2 separately above parameter 1 and parameter 2 respectively or I can mention LOAD LIST ENV 1 2 above parameter 1 as in the case of file attached by me.
    because some people are saying I have to mention it separately .
    I have tried both ways , and I am getting different results for the two cases.
  • Hi   one more issue when I am not assigning any load envelopes .

    all members are safe (all passed).

    but when for same staad file if I assign load envelopes than some members are failing and that too in strength checks , if they would have been failing in deflection check , I can understand , because staad SS6 doesn't performs deflection checks automatically , unless serviceability envelope is defined. but strength check is performed by default , so  I think this issue should not be there .

    please have a look at attached staad file . in this STAAD file I have defined load envelopes .after running this file you can see some members are failing in strength checks. but when you remove load envelopes these members are not failing. please check by removing load envelopes for same attached staad file.

    M703-IA-P1.std

Reply
  • Hi   one more issue when I am not assigning any load envelopes .

    all members are safe (all passed).

    but when for same staad file if I assign load envelopes than some members are failing and that too in strength checks , if they would have been failing in deflection check , I can understand , because staad SS6 doesn't performs deflection checks automatically , unless serviceability envelope is defined. but strength check is performed by default , so  I think this issue should not be there .

    please have a look at attached staad file . in this STAAD file I have defined load envelopes .after running this file you can see some members are failing in strength checks. but when you remove load envelopes these members are not failing. please check by removing load envelopes for same attached staad file.

    M703-IA-P1.std

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