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Notional Load as per AISC 360-05

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Notional Load as per AISC 360-05

  • i have a symmetric structure with symmetric loads..

    how does staad generate notional loads?

    i used the notional load feature in staad.pro v8i release 20.07.05.15, the generated loads are not symmetric.. why?

    below is the input file i used..

    STAAD SPACE
    INPUT WIDTH 79
    UNIT METER KN
    JOINT COORDINATES
           1 0 5 0
           2 0 5 4
           3 4 5 4
           4 4 5 0
           5 0 0 0
           6 0 0 4
           7 4 0 4
           8 4 0 0
           9 0 7 0
          10 0 7 4
          11 4 7 4
          12 4 7 0
          13 0 7 2
          14 2 7 4
          15 4 7 2
          16 2 7 0
    MEMBER INCIDENCES
           1         1         2
           2         2         3
           3         3         4
           4         4         1
           5         5         1
           6         1         9
           7         6         2
           8         2        10
           9         8         4
          10         4        12
          11         7         3
          12         3        11
          13         9        13
          14        10        14
          15        11        15
          16        12        16
          17        13        10
          18        14        11
          19        15        12
          20        16         9
          21         1        13
          22         2        13
          23         2        14
          24         3        14
          25         4        15
          26         3        15
          27         4        16
          28         1        16
    DEFINE MATERIAL START
    ISOTROPIC STEEL
    E 2.05e+008
    POISSON 0.3
    DENSITY 76.8195
    ALPHA 1.2e-005
    DAMP 0.03
    END DEFINE MATERIAL
    MEMBER PROPERTY AUSTRALIAN
    1 TO 4 13 TO 20 TABLE ST UB150X14.0
    5 TO 12 TABLE ST UC100X14.8
    21 TO 28 TABLE ST A75X75X5
    CONSTANTS
    MATERIAL STEEL ALL
    MEMBER TRUSS
    21 TO 28
    MEMBER RELEASE
    1 TO 4 13 TO 16 START MY MZ
    1 TO 4 17 TO 20 END MY MZ
    SUPPORTS
    5 TO 8 FIXED BUT MX MZ
    LOAD 1 LOADTYPE Dead  TITLE LOAD CASE 1
    JOINT LOAD
    13 TO 16 FY -1
    LOAD 2 NOTIONAL X
    NOTIONAL LOAD
    1 X 0.002
    LOAD 3 NOTIONAL Z
    NOTIONAL LOAD
    1 Z 0.002
    PERFORM ANALYSIS
    FINISH

  • The following is the answer to your question on how STAAD genertaes the notional load:

    Answer :

    1.     Since notional loads are derived from gravity loads, the first step is in determining the lumped weight at the various nodes of the structure from the corresponding gravity loads. For example, when you declare the notional load as “1 X 0.002”, the program first generates the vertical weights (in the global Y direction) at all the nodes of the structure from the loading data you specified in case 1.

    2.     Once the nodal weights are obtained, those are then multiplied by the notional load factor, and the resulting value is applied along the direction that you want the notional load to act in. In this example, the vertical weights lumped at the nodes are multiplied by 0.002, and the results are then applied at the same respective locations along the global X direction.

    If you want to obtain a report of the notional loads that the program generates, use the PRINT LOAD DATA option with your analysis command. For example,

    PERFORM DIRECT ANALYSIS PRINT LOAD DATA

    I notice that you are using version 20.07.05.15. I would suggest you to use the latest 20.07.06.34, which has some corrections regarding the Direct Analysis.

    Sudip Narayan Choudhury

  • Use PERFORM ANALYSIS Print Static Loads to see the joint effective loads; these are symmetric. However the results are not symmetric because the cross sections are not aligned symmetrically. This would not matter if Iy and Iz were equal, but they are not.

  • I WILL LIKE TO GET CLARIFICATION. WHETHER NOTIONAL LOAD IS 2% OR 0.2%.

    As per my vague rememberance it is somewhere between 1.5 and 2%.The file posted by Mr Magat speaks for 0.2%. Is it ok?

  • 0.2% as per Appendix 7 of AISC 360-05