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Notion load factor for 0.002 or 0.003

淵鈞 張
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hi

good day everyone.

I have a question about NOTIONAL LOAD FACTOR .

Regarding to AISC 360-16 PAGE 16.1-27 as shown below.

(c) In structures to which Section C2.2b is applicable, in lieu of using τb < 1.0 where
αPr /Pns > 0.5, it is permissible to use τb = 1.0 for all noncomposite members if a
notional load of 0.001αYi [where Yi is as defined in Section C2.2b(a)] is applied
at all levels, in the direction specified in Section C2.2b(b), in all load combinations.
These notional loads shall be added to those, if any, used to account for the
effects of initial imperfections in the position of points of intersection of members
and shall not be subject to the provisions of Section C2.2b(d).

1.

I try to realize the meaning of that. and if tau-b =1 and notion load will be 0.003 ,

is that right ?

2.

and I try to write the syntax in staad as show below.

DEFINE DIRECT ANALYSIS
FLEX 1 ALL
AXIAL ALL
FYLD 235000
NOTIONAL LOAD FACTOR 0.003

besides these syntax , is that any syntax I need to take care?

thank you. 

  • 0 Offline

    hello Sye ,
    very very thank you about your answer again and again.

    Regarding the matter that you taught me as shown below.

    answer of 3.

    Your pdf shows reactions for load cases 141, 143, 101 etc.
    --->
    actually I selected the load case from 101 to 243,
    and check the max values, but no any effects in the results.

    You need to add notional load to cases as appropriate and then check the results.
    --->
    ok , I will try to do this again, really thank you very much.


    Inline image 1

    very very
    thank you and appreciated.

  • 0 Offline
    hello Sye ,
    very very thank you about your answer again and again.

    a few of queries still remain.

    1.
    When I specifying the notional load , and which direction should be applied in staad ?
    for example , moment frame or braced frame.
    Is any specific rule for these ?

    2.
    sometimes I heard about
    "" Ni  is not applied when the actual lateral load is larger than the calculated notional load.""
    but in AISC360-16 , I can not find this kind of specification, I thought that is the specification of AISC360-05 or 10.
    do you have any idea about that ?

    very very
    thank you and appreciated.

  • 0 Offline in reply to 淵鈞 張
    1. I chose load 208 randomly just to explain how the notional load generation works. You need to choose appropriate load cases.
    2. Correct
    3. Your pdf shows reactions for load cases 141, 143, 101 etc. I had just included the notional load for case 208 and so these reactions will not be affected by what I did. You need to add notional load to cases as appropriate and then check the results.



  • 0 Offline
    hello Sye ,
    very very thank you about your assistance again.

    very sorry , I still have some queries that need your help and advice.

    1.
    "A notional load is a lateral load (horizontal load) which is derived from an
    existing vertical load case."

    according to this concept , and you use the load case 208, is that right?
    (load case 208 is carried about primary vertical load) 

    because , in the beginning I have no idea why you choose load case 208.
    (load case 208 is bundle pulling for maintenance) 

    2.
    "Multiple load items can be specified under any NOTIONAL LOAD and there can be
    one or more blocks of NOTIONAL LOAD command(s) in any load case."

    as this rule, I can also add the blocks of notional load in load case 209 to 211
    or other load case that carried about primary vertical load.
    do I right ?

    3.
    About Result  
    I`ve run the staad and compare the result of reactions.
    I found the reactions are the same , there are noting changed in staad result.

    Or there are other way to verify the result ?
    I attached the results, does anything that I make mistake ?

    very very
    thank you and appreciated.


  • 0 Offline in reply to 淵鈞 張

    Regarding 1, in Direct Analysis the Taub values are determined iteratively based on the axial force in the member. When you set the notional load factor to 0.003 these iterations are not carried out and Taub is considered as 1 which is what the code recommends.

    Regarding 2, Added the notional load in X direction for your load case 208. Modified file attached Notional_load_0003_syntax_modified.STD

    Regarding 3, the direct analysis implementation in STAAD automatically handles that. There is nothing additional that you have to do.



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