Correct Usage of SELECT and SELECT OPTIMIZED parameters?

Hello to everyone here!

I have some questions below:

1) DIFFERENCE of SELECT and SELECT OPTIMIZED

I've been reading old threads here regarding optimization of members and just want to clarify what is exactly the difference between SELECT and SELECT OPTIMIZED parameter in STAAD?

2) ANALYSIS

I've tried to use SELECT to a certain group of members followed by GROUP and PERFORM ANALYSIS so STAAD will analyze based on the largest and safe section on the group but, the problem is - that certain GROUP of members were optimized but when STAAD performed the analysis again with the new section it fails. Does STAAD optimize the member to resist its own loading rather than optimizing based on the overall loading and action of the whole structure?

SAMPLE INPUT:

SELECT MEM 1 TO 5

GROUP MEM 1 TO 5

(mem 1 to 5 were optimized and the largest section was selected)

PERFORM ANALYSIS

(RESULT: OTHER MEMBERS FAILED)

Can STAAD optimize a certain group of members considering also the strength of other members in the structure?

Thank you very much!

Parents
  • When you are using the SELECT command, STAAD.Pro picks up the smallest sections which would be satisfying the code conditions. When such sections are selected, the stiffness of the structure is changed, so the forces on the structure will be different. Due to this, you need to reanalyze the model again and perform a new code check with those new forces.

    It might be that the members would still be failing after this SELECT - PEREFROM ANALYSIS - CODE CHECK iteration as new forces will be used for the code check. In such case, you would need to enter one more such iteration in the input file. So you would need to use one more set of SELECT, PERFORM ANALYSIS and CODE CHECK commands till all the sections will be passing.

    SELECT OPTIMIZED instructs STAAD.Pro to perform additional iterations of the member selection routine followed by another analysis. In this case, “optimized” means that the program will automatically iterate twice, without the need for the user to manually specify the repetitions with SELECT and PERFORM ANALYSIS commands.

    It is good to be aware that the command exists, as it may have an application under special circumstances. However, good practice generally dictates manually specifying an iterative “analyze‐design‐reanalyze‐check” as mentioned previously.



  • Hi,

    First of all thank you for your immediate response to my question and also for the explanation. Appreciated much :)

    Please see my follow up questions below:

    1) "When you are using the SELECT command, STAAD.Pro picks up the smallest sections which would be satisfying the code conditions. When such sections are selected, the stiffness of the structure is changed, so the forces on the structure will be different. Due to this, you need to reanalyze the model again and perform a new code check with those new forces." 

     I did analyze the new selected sections again and you were right, stiffness of the structure was changed causing some of the members (those which were not selected for optimization) to failed the code requirements based on the specified load list. My question is, can STAAD optimize the selected group of members which will satisfy code requirements including the rest of the members in the structure, no failed members? SELECT - GROUP - PERFORM - (all passed) rather than SELECT - GROUP - PERFORM - (other members failed). Is this possible? 

    2) It might be that the members would still be failing after this SELECT - PEREFROM ANALYSIS - CODE CHECK iteration as new forces will be used for the code check. In such case, you would need to enter one more such iteration in the input file. So you would need to use one more set of SELECT, PERFORM ANALYSIS and CODE CHECK commands till all the sections will be passing.

    How can i do this iteration(s)? Any example?Thanks

    3) SELECT OPTIMIZED instructs STAAD.Pro to perform additional iterations of the member selection routine followed by another analysis. In this case, “optimized” means that the program will automatically iterate twice, without the need for the user to manually specify the repetitions with SELECT and PERFORM ANALYSIS commands.

    SELECT OPTIMIZED optimizes the whole structure, right? Is SELECT OPTIMIZED applicable for certain selected group of members only?

    Is this input correct:

    LOAD LIST 30 TO 43
    PARAMETER 
    CODE EN 1993-1-1:2005
    SELECT OPTIMIZED
    GROUP MEMB 1 TO 15
    GROUP MEMB 16 TO 47
    GROUP MEMB 48 TO 62
     
    PERFORM ANALYSIS
    LOAD LIST 30 TO 43
    PARAMETER 
    CODE EN 1993-1-1:2005
    SGR 1 ALL
    RATIO 1 ALL
    TORSION 3 ALL   (when checking the members for Serviceability, i usually neglect torsion and use it again in Ultimate State, is it correct?
    TRACK 4 ALL
    CHECK CODE ALL

    I want to know "HOW" the correct optimization is done so i can obtain the least section for each Group of Members ,satisfying the code requirements for Serviceability Limit States and Ultimate Limit States. 

    Thank you and have a wonderful day!

    Master Mac

  • 1) and 2) You can perform several SELECT iterations. For example:

    PARAMETER 1
    CODE EN 1993-1-1:2005
    TRACK 2 ALL
    SGR 2 ALL

    *1st iteration

    SELECT ALL
    GROUP MEMB
    PERFORM ANALYSIS

    *2nd iteration

    SELECT ALL
    GROUP MEMB
    PERFORM ANALYSIS

    CHECK CODE ALL


    There is an alternative way to avoid failing members by using the RATIO design parameter. This is explained by Mr. Kris Sathia in this forum post: communities.bentley.com/.../302793

    3) Your input looks good, though I would use SELECT command with few iterations instead of SELECT OPTIMIZED.



    Answer Verified By: Master Mac 

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