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Error during cable analysis

saqlain awan
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Hello Sir,

I am designing steel frame building using ASD method but during analysis staad is giving me the error " Each load combination must be followed by perfom cable analysis then change". unfortunately i am unable to solve this error. please help me with that.

  • 0 Offline in reply to Basu

    This structure is buckling even under the selfweight loading. If you run a first order analysis ( PERFORM ANALYSIS with just the selfweight ) you will see large displacements in Y. So I would suggest that you first do a basic first order analysis with the loads and ensure that displacements are within reasonable limits for all cases. You will need to add lateral supports as otherwise the structure does not have any lateral stability with the frame hanging from four pinned supports and suspended using axial only cable elements. Stabilizing the structure even against vertical loads would require addition of weak lateral springs. Try adding weak translational springs in FX and FZ at four corners. If you need to analyze this structure for lateral loads, you would definitely need to have additional lateral supports besides these springs. Also for any nonlinear type analysis you will need to use REPEAT LOADs and not LOAD COMBINATIONs.



  • 0 Offline

    Can any one find the solution for this

    STAAD SPACE
    START JOB INFORMATION
    ENGINEER DATE 9/19/2018
    JOB NAME Load at 4m from center of lifting frame
    JOB NO 123
    JOB REV R1
    END JOB INFORMATION
    INPUT WIDTH 79
    UNIT METER KN
    JOINT COORDINATES
    1 0 0 0; 2 0.740001 0 0; 3 1.74 0 0; 4 2.74001 0 0; 5 3.74001 0 0;
    7 5.68001 0 0; 8 6.68001 0 0; 9 7.68002 0 0; 10 8.68002 0 0; 11 9.42002 0 0;
    13 0.740001 0 8.40002; 14 1.74 0 8.40002; 15 2.74001 0 8.40002;
    16 3.74001 0 8.40002; 17 5.68001 0 8.40002; 18 6.68001 0 8.40002;
    19 7.68002 0 8.40002; 20 8.68002 0 8.40002; 21 0 0 8.40002;
    22 9.42002 0 8.40002; 25 0.740001 0 2; 32 8.68002 0 2; 33 0 0 2;
    34 9.42002 0 2; 37 0.740001 0 6.40001; 44 8.68002 0 6.40001; 45 0 0 6.40001;
    46 9.42002 0 6.40001; 48 3.56001 0 2; 49 3.56001 0 6.40001; 50 5.86001 0 2;
    51 5.86001 0 6.40001; 52 4.71001 0 0; 53 4.71001 0 8.40002;
    56 4.43501 5.75101 0; 57 4.43501 5.75101 8.40002; 58 4.98501 5.75101 0;
    59 4.98501 5.75101 8.40002;
    MEMBER INCIDENCES
    1 1 33; 2 33 45; 3 45 21; 4 2 1; 5 13 21; 6 25 33; 7 37 45; 8 2 3; 9 13 14;
    10 25 48; 11 37 49; 12 3 4; 13 14 15; 16 4 5; 17 15 16; 18 48 50; 19 49 51;
    20 5 52; 21 16 53; 22 7 8; 23 17 18; 26 8 9; 27 18 19; 28 50 32; 29 51 44;
    30 9 10; 31 19 20; 32 10 11; 33 20 22; 34 32 34; 35 44 46; 36 11 34; 37 34 46;
    38 46 22; 39 52 7; 40 53 17; 45 2 56; 46 10 58; 47 13 57; 48 20 59;
    DEFINE MATERIAL START
    ISOTROPIC STEEL
    E 1.99947e+08
    POISSON 0.3
    DENSITY 76.8191
    ALPHA 6.5e-06
    DAMP 0.03
    TYPE STEEL
    STRENGTH FY 248210 FU 399894 RY 1.5 RT 1.2
    END DEFINE MATERIAL
    CONSTANTS
    MATERIAL STEEL ALL
    MEMBER PROPERTY BRITISH
    1 TO 13 16 TO 23 26 TO 40 TABLE ST PIP40616.0
    MEMBER PROPERTY BRITISH
    45 TO 48 PRIS YD 0.08
    SUPPORTS
    56 TO 59 PINNED
    MEMBER CABLE
    45 TO 48 TENSION 1
    LOAD 1 LOADTYPE Dead TITLE DL
    SELFWEIGHT Y -1
    PERFORM CABLE ANALYSIS BASIC
    CHANGE
    LOAD 2 LOADTYPE Live TITLE 4M VERTICAL
    MEMBER LOAD
    8 9 CON GY -1200 0
    30 31 CON GY -1200 1
    PERFORM CABLE ANALYSIS BASIC
    CHANGE
    LOAD 3 LOADTYPE Live TITLE 4M HORIZONTAL
    MEMBER LOAD
    30 31 CON GZ -120 1
    8 9 CON GZ -120 0
    PERFORM CABLE ANALYSIS BASIC
    CHANGE
    LOAD COMB 4 COMBINATION LOAD CASE 4
    1 1.1 2 1.0 3 1.0
    PERFORM CABLE ANALYSIS BASIC
    CHANGE
    PERFORM ANALYSIS PRINT ALL
    PARAMETER 1
    CODE BS5950
    RATIO 1 ALL
    TRACK 2 ALL
    CHECK CODE ALL
    FINISH

  • 0 Offline in reply to saqlain awan
    There are few in-build standard cable sections already added in Staad section database. You need to configure the section profile table for this.
    Please see the link below.

    communities.bentley.com/.../366848

    However, I don't see any much of difference if you use the rod section (instead of standard cable section) and assign them as "Tension Only" member . The behavior of this section is same as the cable section which is supposed to only handle the tension.



  • 0 Offline in reply to Sye
    But how can i define pure cable instead of defining rod. i couldn't find any option of defining cable. Can i define rod and assigning it as tension member to get the effect of cable.
  • 0 Offline in reply to saqlain awan

    You were attempting to do a Nonlinear Cable Analysis but there was no pretension load defined which is essential. I added a pretension of 10KN ( you may change as needed). The bigger question is whether the nonlinear cable analysis is required or not. Are these members that you assigned as cables, really cable members or are these rods ? If these are rods you may as well model these as TRUSS. Also when you are using a nonlinear cable analysis, each load case has to be a complete case by itself with selfweight and all components. You should not do a cable analysis with just the wind load ( for example load case 7 to 14 ). Also if you go with a nonlinear cable analysis, your load combinations should be replaced by REPEAT LOADs. These can be very easily handled through the command editor as explained for the load case 15 below

    LOAD COMBINATION :

    …

    LOAD COMB 15 DL+RL

    5 1.0 6 1.0

     

    REPEAT LOAD :

    …

    LOAD 15 DL+RL

    REPEAT LOAD

    5 1.0 6 1.0

    A partly modified file is attached for your reference. Hop this will give you some direction.

    2068.Structure1.std



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