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Plate Deflection Results wrong

Atul Sharma
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I am trying modelling a simply supported plate model in staad with 10×10 mesh with density 25 Knm2 and E2510^6 and comparing it with results of other finite element applications and also with numerical matrix analysis by hand calculations. Both fem app and hand calculations results match but those of staad pro doesn't. Though I was sure of correct modelling and also checked for equilibrium each time, I tried models of other dimensions l b and h as well. Each time fem results and hand calculations matched perfectly. 

For example I tried modeling 35×50 m plate with 2m depth. Hand and fem  calculation results were 30 and 33 mm at centre resp. But staad gives 300mm. For other models also the result are far too variable like this case only. Please I need urgent support. Any reference would be appreciated.

  • 0 Offline

    Did you mesh your plate?what was the size of your mesh?

    Attach your Staad model and your hand calculation so that you can get assistance from bentley technical team

  • +1 Offline in reply to Joseph Lucas Magare
    • Yes, into 10*10 divisions each. Hand calculations reference is Timoshenko plate theory on which most FEM applications of today are based on. Model is accurate. The main blunder is calculations differences.

    For 5*5 m plate of 100mm thickness with SS corners and same mesh divisions and density and E also is giving this very variation. Staad gives 16.8mm approx at center due to self wt but other Fem applications ( ETABS ) and hand calcs gives 2.7mm approx. 

    I have many more models showing this high variation of results for various aspect ratios.

    Explain? Are staad pro plate deflection calculations results expressed in different norms than conventional?

    Answer Verified By: Atul Sharma 

  • 0 Offline in reply to Atul Sharma

    It is hard to comment without seeing that STAAD.Pro model. Please attach it and your hand calculations if possible.



  • 0 Offline in reply to Modestas

    staad model

    STAAD SPACE
    START JOB INFORMATION
    ENGINEER DATE 11-Oct-22
    END JOB INFORMATION
    INPUT WIDTH 79
    UNIT METER KN
    JOINT COORDINATES
    1 0 0 0; 2 2 0 0; 3 2 0 1; 4 0 0 1; 5 0.2 0 0; 6 0.2 0 0.1; 7 0 0 0.1;
    8 0.4 0 0; 9 0.4 0 0.1; 10 0.6 0 0; 11 0.6 0 0.1; 12 0.8 0 0; 13 0.8 0 0.1;
    14 1 0 0; 15 1 0 0.1; 16 1.2 0 0; 17 1.2 0 0.1; 18 1.4 0 0; 19 1.4 0 0.1;
    20 1.6 0 0; 21 1.6 0 0.1; 22 1.8 0 0; 23 1.8 0 0.1; 24 2 0 0.1; 25 0.2 0 0.2;
    26 0 0 0.2; 27 0.4 0 0.2; 28 0.6 0 0.2; 29 0.8 0 0.2; 30 1 0 0.2; 31 1.2 0 0.2;
    32 1.4 0 0.2; 33 1.6 0 0.2; 34 1.8 0 0.2; 35 2 0 0.2; 36 0.2 0 0.3; 37 0 0 0.3;
    38 0.4 0 0.3; 39 0.6 0 0.3; 40 0.8 0 0.3; 41 1 0 0.3; 42 1.2 0 0.3;
    43 1.4 0 0.3; 44 1.6 0 0.3; 45 1.8 0 0.3; 46 2 0 0.3; 47 0.2 0 0.4; 48 0 0 0.4;
    49 0.4 0 0.4; 50 0.6 0 0.4; 51 0.8 0 0.4; 52 1 0 0.4; 53 1.2 0 0.4;
    54 1.4 0 0.4; 55 1.6 0 0.4; 56 1.8 0 0.4; 57 2 0 0.4; 58 0.2 0 0.5; 59 0 0 0.5;
    60 0.4 0 0.5; 61 0.6 0 0.5; 62 0.8 0 0.5; 63 1 0 0.5; 64 1.2 0 0.5;
    65 1.4 0 0.5; 66 1.6 0 0.5; 67 1.8 0 0.5; 68 2 0 0.5; 69 0.2 0 0.6; 70 0 0 0.6;
    71 0.4 0 0.6; 72 0.6 0 0.6; 73 0.8 0 0.6; 74 1 0 0.6; 75 1.2 0 0.6;
    76 1.4 0 0.6; 77 1.6 0 0.6; 78 1.8 0 0.6; 79 2 0 0.6; 80 0.2 0 0.7; 81 0 0 0.7;
    82 0.4 0 0.7; 83 0.6 0 0.7; 84 0.8 0 0.7; 85 1 0 0.7; 86 1.2 0 0.7;
    87 1.4 0 0.7; 88 1.6 0 0.7; 89 1.8 0 0.7; 90 2 0 0.7; 91 0.2 0 0.8; 92 0 0 0.8;
    93 0.4 0 0.8; 94 0.6 0 0.8; 95 0.8 0 0.8; 96 1 0 0.8; 97 1.2 0 0.8;
    98 1.4 0 0.8; 99 1.6 0 0.8; 100 1.8 0 0.8; 101 2 0 0.8; 102 0.2 0 0.9;
    103 0 0 0.9; 104 0.4 0 0.9; 105 0.6 0 0.9; 106 0.8 0 0.9; 107 1 0 0.9;
    108 1.2 0 0.9; 109 1.4 0 0.9; 110 1.6 0 0.9; 111 1.8 0 0.9; 112 2 0 0.9;
    113 0.2 0 1; 114 0.4 0 1; 115 0.6 0 1; 116 0.8 0 1; 117 1 0 1; 118 1.2 0 1;
    119 1.4 0 1; 120 1.6 0 1; 121 1.8 0 1;
    ELEMENT INCIDENCES SHELL
    6 1 5 6 7; 7 5 8 9 6; 8 8 10 11 9; 9 10 12 13 11; 10 12 14 15 13;
    11 14 16 17 15; 12 16 18 19 17; 13 18 20 21 19; 14 20 22 23 21; 15 22 2 24 23;
    16 7 6 25 26; 17 6 9 27 25; 18 9 11 28 27; 19 11 13 29 28; 20 13 15 30 29;
    21 15 17 31 30; 22 17 19 32 31; 23 19 21 33 32; 24 21 23 34 33; 25 23 24 35 34;
    26 26 25 36 37; 27 25 27 38 36; 28 27 28 39 38; 29 28 29 40 39; 30 29 30 41 40;
    31 30 31 42 41; 32 31 32 43 42; 33 32 33 44 43; 34 33 34 45 44; 35 34 35 46 45;
    36 37 36 47 48; 37 36 38 49 47; 38 38 39 50 49; 39 39 40 51 50; 40 40 41 52 51;
    41 41 42 53 52; 42 42 43 54 53; 43 43 44 55 54; 44 44 45 56 55; 45 45 46 57 56;
    46 48 47 58 59; 47 47 49 60 58; 48 49 50 61 60; 49 50 51 62 61; 50 51 52 63 62;
    51 52 53 64 63; 52 53 54 65 64; 53 54 55 66 65; 54 55 56 67 66; 55 56 57 68 67;
    56 59 58 69 70; 57 58 60 71 69; 58 60 61 72 71; 59 61 62 73 72; 60 62 63 74 73;
    61 63 64 75 74; 62 64 65 76 75; 63 65 66 77 76; 64 66 67 78 77; 65 67 68 79 78;
    66 70 69 80 81; 67 69 71 82 80; 68 71 72 83 82; 69 72 73 84 83; 70 73 74 85 84;
    71 74 75 86 85; 72 75 76 87 86; 73 76 77 88 87; 74 77 78 89 88; 75 78 79 90 89;
    76 81 80 91 92; 77 80 82 93 91; 78 82 83 94 93; 79 83 84 95 94; 80 84 85 96 95;
    81 85 86 97 96; 82 86 87 98 97; 83 87 88 99 98; 84 88 89 100 99;
    85 89 90 101 100; 86 92 91 102 103; 87 91 93 104 102; 88 93 94 105 104;
    89 94 95 106 105; 90 95 96 107 106; 91 96 97 108 107; 92 97 98 109 108;
    93 98 99 110 109; 94 99 100 111 110; 95 100 101 112 111; 96 103 102 113 4;
    97 102 104 114 113; 98 104 105 115 114; 99 105 106 116 115;
    100 106 107 117 116; 101 107 108 118 117; 102 108 109 119 118;
    103 109 110 120 119; 104 110 111 121 120; 105 111 112 3 121;
    ELEMENT PROPERTY
    6 TO 105 THICKNESS 0.01
    DEFINE MATERIAL START
    ISOTROPIC CONCRETE
    E 2.49185e+007
    POISSON 0.17
    DENSITY 25
    ALPHA 1e-005
    DAMP 0.05
    TYPE CONCRETE
    STRENGTH FCU 25000
    END DEFINE MATERIAL
    CONSTANTS
    MATERIAL CONCRETE ALL
    SUPPORTS
    1 4 PINNED
    2 3 FIXED BUT FX FZ MX MY MZ
    LOAD 1 LOADTYPE Dead  TITLE LOAD CASE 1
    SELFWEIGHT Y -1 LIST ALL
    PERFORM ANALYSIS PRINT ALL
    FINISH
    hand calculation ans ETABS both give 1mm approx but staad showing 26mm approx at center.
    for 1*1  5*5  5*10 etc model also very incorrect results ranging upto 1000% error even.
    references Timoshenko_-_Theory_of_plates_and_shells
  • 0 Offline in reply to Atul Sharma

    I think the difference might be due to different support conditions. Make sure that STAAD.Pro model uses the same support conditions for the slab as considered in the manual calculation.



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