Warning message-"The member is not a Truss member"

Hello Everyone,

I have analyzed and designed overhead transmission tower by IS 802 code. I am getting a warning message that " The member is not a Truss member" The member has been designed considering axial force only. How to avoid this warning message.

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  • STAAD TRUSS
    START JOB INFORMATION
    ENGINEER DATE 14-Jun-17
    END JOB INFORMATION
    INPUT WIDTH 79
    UNIT METER KN
    JOINT COORDINATES
    1 0 0 0; 2 0 0 5; 3 5 0 5; 4 5 0 0; 5 1 5 1; 6 1 5 4; 7 4 5 1; 8 4 5 4;
    9 1 6 1; 10 1 6 4; 11 4 6 1; 12 4 6 4; 13 1 7 1; 14 1 7 4; 15 4 7 1; 16 4 7 4;
    17 1 8 1; 18 1 8 4; 19 4 8 1; 20 4 8 4; 21 1 9 1; 22 1 9 4; 23 4 9 1; 24 4 9 4;
    25 1 10 1; 26 1 10 4; 27 4 10 1; 28 4 10 4;
    MEMBER INCIDENCES
    1 2 6; 2 1 5; 3 4 7; 4 3 8; 5 6 8; 6 6 5; 7 5 7; 8 8 7; 9 5 9; 10 6 10;
    11 7 11; 12 8 12; 13 9 13; 14 10 14; 15 11 15; 16 12 16; 17 13 17; 18 14 18;
    19 15 19; 20 16 20; 21 17 21; 22 18 22; 23 19 23; 24 20 24; 25 21 25; 26 22 26;
    27 23 27; 28 24 28; 29 9 11; 30 10 12; 31 13 15; 32 14 16; 33 17 19; 34 18 20;
    35 21 23; 36 22 24; 37 25 27; 38 26 28; 39 9 10; 40 11 12; 41 13 14; 42 15 16;
    43 17 18; 44 19 20; 45 21 22; 46 23 24; 47 25 26; 48 27 28;
    DEFINE MATERIAL START
    ISOTROPIC STEEL
    E 2.05e+008
    POISSON 0.3
    DENSITY 76.8195
    ALPHA 1.2e-005
    DAMP 0.03
    TYPE STEEL
    STRENGTH FY 253200 FU 407800 RY 1.5 RT 1.2
    END DEFINE MATERIAL
    MEMBER PROPERTY INDIAN
    1 TO 48 TABLE LD ISA150X150X16
    CONSTANTS
    MATERIAL STEEL ALL
    SUPPORTS
    1 TO 4 FIXED
    MEMBER TRUSS
    1 TO 48
    LOAD 1 LOADTYPE Dead TITLE DL
    SELFWEIGHT Y -1
    LOAD 2 LOADTYPE Live REDUCIBLE TITLE LL
    JOINT LOAD
    25 TO 28 FY -25
    LOAD COMB 3 Generated Indian Code Genral_Structures 1
    1 1.5 2 1.5
    LOAD COMB 4 Generated Indian Code Genral_Structures 2
    1 1.2 2 1.2
    LOAD COMB 5 Generated Indian Code Genral_Structures 3
    1 1.5
    LOAD COMB 6 Generated Indian Code Genral_Structures 4
    1 0.9
    PERFORM ANALYSIS PRINT ALL
    PARAMETER 1
    CODE IS802
    CNSF 0 ALL
    DANGLE 0 ALL
    DBL 0.012 ALL
    DMAX 1000 ALL
    DMIN 0 ALL
    ELA 2 ALL
    FVB 218000 ALL
    FYB 436000 ALL
    FYLD 250000 ALL
    GALVA 0 ALL
    GALVA 0 ALL
    GUSSET 0.005 ALL
    KY 1 ALL
    KZ 1 ALL
    LEG 2 ALL
    LY 0 ALL
    LZ 0 ALL
    MAIN 1 ALL
    NHL 0 ALL
    NSF 1 ALL
    TRACK 0 ALL
    CHECK CODE ALL
    PARAMETER 2
    CODE IS802
    FIXED GROUP
    PARAMETER 3
    CODE IS802
    GROUP MEMB 1 TO 48
    PARAMETER 4
    CODE IS802
    GROUP SY MEMB 1 TO 48
    PARAMETER 5
    CODE IS802
    GROUP AX MEMB 1 TO 48
    PARAMETER 6
    CODE IS802
    STEEL MEMBER TAKE OFF ALL
    PARAMETER 7
    CODE IS802
    SELECT ALL
    PARAMETER 8
    CODE IS802
    SELECT OPTIMIZED
    PARAMETER 9
    CODE IS802
    STEEL TAKE OFF ALL
    FINISH

    Thanks for your reply sir,

    Even after changing it to truss members also it showing warning like "instability of joint" in the Direction FZ, and Note as very week spring added for stability

  • Just to get the design as per IS:802, you should not declare the full structure as TRUSS as the model would be unstable in that case. If you look at the displacements you will see absurd values which means that the structure cannot be analyzed if you declare all the members as truss. I would rather define these as normal members by removing the TRUSS specifications, specify the frame type as SPACE and ignore the resulting warnings in the design phase. Just be aware that the sections are not being checked for moments/shears but only for axial forces and ensure that the sections are able to carry some small moments/shears.