Design of Cantilever Beam

While analysis the cantilever portion generates the warning message, " Instability Joint" , How does it can be rectified?

furthermore i want to have some metal structure as pergolas in RCC frame ( Cantilever) can it be analysed with staad?

  • The free end of the cantilever should not be pinned / hinged / released, otherwise the node at the tip can spin leading to your problem. See our wiki on instability for more:

    communities.bentley.com/.../ram-instability-in-finite-element-analysis.aspx



  • hi cgai,

    can you please

    attach your model?

    tnx

    rekcah

  • Dear Seth

    Thanks for the reply.

    yes my model also generated instability, but i am not able to find the solution.

    is there any way to avoid the instability ?  

  • Hi,

    I have modified members connectivity, inorder to avoid instability in your model. 

    Now there is no Instability warning in your model. Download the attached STD file or Try this code:

     STAAD SPACE DXF IMPORT OF MANDAI ROOF STRU.DXF
    START JOB INFORMATION
    ENGINEER DATE 01-Jan-02
    END JOB INFORMATION
    INPUT WIDTH 79
    UNIT INCHES POUND
    JOINT COORDINATES
    3 21264.1 0 9002.8; 4 21264.1 0 9418.8; 21 21264.1 0 9168.8;
    22 20910.1 0 9168.8; 23 21264.1 0 9274.8; 24 20910.1 0 9274.8;
    25 20910.1 0 9418.8; 26 21088.1 0 9002.8; 27 21088.1 0 9418.8;
    40 21264.1 100 9062.8; 41 21396.6 100 9062.8; 42 21264.1 100 9002.8;
    43 21264.1 100 9418.8; 46 21264.1 100 9114.02; 47 21396.6 100 9114.02;
    48 21264.1 100 9163.73; 49 21396.6 100 9163.73; 50 21264.1 100 9213.44;
    51 21396.6 100 9213.44; 52 21264.1 100 9263.16; 53 21396.6 100 9263.16;
    54 21264.1 100 9312.87; 55 21396.6 100 9312.87; 56 21264.1 100 9362.59;
    57 21396.6 100 9362.59; 58 21264.1 100 9410.8; 59 21396.6 100 9410.8;
    60 21264.1 100 9168.8; 61 20910.1 100 9168.8; 62 21264.1 100 9274.8;
    63 20910.1 100 9274.8; 64 20910.1 100 9418.8; 65 21088.1 100 9002.8;
    66 21088.1 100 9418.8; 67 21229.6 100 9002.8; 68 21229.6 100 9070.78;
    69 21196.1 100 9002.8; 70 21196.1 100 9070.78; 71 21162.6 100 9002.8;
    72 21162.6 100 9070.78; 73 21129.1 100 9002.8; 74 21129.1 100 9070.78;
    75 21095.6 100 9002.8; 76 21095.6 100 9070.78; 77 21088.1 100 9070.78;
    78 21264.1 100 9070.78; 79 21088.1 0 9168.8; 80 21088.1 0 9274.8;
    81 21088.1 100 9274.8; 82 21088.1 100 9168.8;
    MEMBER INCIDENCES
    23 40 41; 27 46 47; 29 48 49; 31 50 51; 33 52 53; 35 54 55; 37 56 57; 39 58 59;
    41 60 82; 43 62 81; 44 43 66; 46 66 64; 50 67 68; 52 69 70; 54 71 72; 56 73 74;
    58 75 76; 65 3 42; 66 21 60; 67 22 61; 68 24 63; 69 25 64; 70 27 66; 75 81 63;
    76 81 66; 78 82 61; 79 82 81; 80 79 82; 81 80 81; 82 26 65; 83 4 43; 85 61 64;
    87 42 65; 91 23 62; 95 77 76; 96 76 74; 97 74 72; 98 72 70; 99 70 68;
    100 68 78; 101 65 77; 102 77 82; 103 43 58; 104 58 56; 105 56 54; 106 54 62;
    107 62 52; 108 52 50; 109 50 60; 110 60 48; 111 48 46; 112 46 78; 113 78 40;
    DEFINE MATERIAL START
    ISOTROPIC CONCRETE
    E 3.15e+006
    POISSON 0.17
    DENSITY 0.0868
    ALPHA 5.5e-006
    DAMP 0.05
    END DEFINE MATERIAL
    MEMBER PROPERTY AMERICAN
    41 43 44 46 65 TO 70 75 76 78 TO 83 85 87 91 95 TO 113 PRIS YD 12 ZD 9
    23 27 29 31 33 35 37 39 50 52 54 56 58 PRIS YD 6 ZD 4
    CONSTANTS
    MATERIAL CONCRETE ALL
    SUPPORTS
    3 4 21 TO 27 79 80 FIXED
    LOAD 1 LOADTYPE None  TITLE DL
    SELFWEIGHT Y -1 LIST 23 27 29 31 33 35 37 39 41 43 44 46 50 52 54 56 58 65 -
    66 TO 70 75 76 78 TO 83 85 91
    PDELTA ANALYSIS PRINT ALL
    START CONCRETE DESIGN
    CODE INDIAN
    DESIGN BEAM 23 27 29 31 33 35 37 39 41 43 44 46 50 52 54 56 58 75 76 78 79 -
    85 87 95 TO 113
    DESIGN COLUMN 65 TO 70 80 TO 83 91
    TRACK 1 ALL
    END CONCRETE DESIGN
    FINISH

    -Vivek

    Mon Dai Deck.std