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EX. UK-21 Analysis of a Structure with Tension-Only Members

This example illustrates the modeling of tension-only members using the MEMBER TENSION command.

This problem is installed with the program by default to C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\Sample Models\UK\UK-21 Analysis of a Structure with Tension-Only Members.STD when you install the program.

It is important to note that the analysis can be done for only 1 load case at a time. This is because, the set of "active" members (and hence the stiffness matrix) is load case dependent.

Example Problem No. 21

where:
  • L = 5.25 m, H = 3.5 m
  • Load case 1: P1 = 45 kN & P2 = 70 kN
  • Load case 2: P3 = -45 kN & P4 = -70 kN
    STAAD PLANE EXAMPLE FOR TENSION-ONLY MEMBERS

The input data is initiated with the word STAAD. This structure is a PLANE frame.

    UNIT METER KNS

Units for the commands to follow are defined above.

    JOINT COORDINATES
    1 0 0 ; 2 0 3.5 ; 3 0 7.0 ; 4 5.25 7.0 ; 5 5.25 3.5 ; 6 5.25 0

Joint coordinates of joints 1 to 6 are defined above.

    MEMBER INCIDENCES
    1 1 2 5
    6 1 5 ; 7 2 6 ; 8 2 4 ; 9 3 5 ; 10 2 5

Incidences of members 1 to 10 are defined.

    MEMBER TENSION
    6 TO 9

Members 6 to 9 are defined as tension-only members using the MEMBER TENSION command. Hence for each load case, if during the analysis, any of the members 6 to 9 is found to be carrying a compressive force, it is disabled from the structure and the analysis is carried out again with the modified structure.

    MEMBER PROPERTY BRITISH
    1 TO 10 TA ST UC152X152X30

All members have been assigned a UC section from the British table.

    UNIT MMS
    DEFINE MATERIAL START
    ISOTROPIC STEEL
    E 210
    POISSON 0.3
    DENSITY 7.6977e-008
    ALPHA 6e-006
    DAMP 0.03
    TYPE STEEL
    STRENGTH FY 0.24821 FU 0.399894 RY 1.5 RT 1.2
    END DEFINE MATERIAL
    CONSTANTS
    MATERIAL STEEL ALL

The DEFINE MATERIAL command is used to specify material properties and the CONSTANT is used to assign the material to all members. The length units have been changed from meters to millimeters to facilitate the input of these values.

    SUPPORT
    1 6 PINNED

The supports are defined above.

    LOAD 1
    JOINT LOAD
    2 FX 70
    3 FX 45

Load 1 is defined above and consists of joint loads at joints 2 and 3.

    PERFORM ANALYSIS
    CHANGE
    MEMBER TENSION
    6 TO 9

One or more among the members 6 to 9 may have been inactivated in the previous analysis.

    LOAD 2
    JOINT LOAD
    4 FX -45
    5 FX -70

Load case 2 is described above.

    LOAD 3
    REPEAT LOAD
    1 1.0 2 1.0

Load case 3 illustrates the technique employed to instruct STAAD to create a load case which consists of data to be assembled from other load cases already specified earlier. We would like the program to analyze the structure for loads from cases 1 and 2 acting simultaneously.

    PRINT ANALYSIS RESULTS
    FINI

The analysis results are printed and the run terminated.

Input File

STAAD PLANE EXAMPLE FOR TENSION-ONLY MEMBERS
UNIT METER KNS
SET NL 3
JOINT COORDINATES
1 0 0 ; 2 0 3.5 ; 3 0 7.0 ; 4 5.25 7.0 ; 5 5.25 3.5 ; 6 5.25 0
MEMBER INCIDENCES
1 1 2 5
6 1 5 ; 7 2 6 ; 8 2 4 ; 9 3 5 ; 10 2 5
MEMBER TENSION
6 TO 9
MEMBER PROPERTY BRITISH
1 TO 10 TABLE ST UC152X152X30
UNIT MMS
DEFINE MATERIAL START
ISOTROPIC STEEL
E 210
POISSON 0.3
DENSITY 7.6977e-008
ALPHA 6e-006
DAMP 0.03
TYPE STEEL
STRENGTH FY 0.24821 FU 0.399894 RY 1.5 RT 1.2
END DEFINE MATERIAL
CONSTANTS
MATERIAL STEEL ALL
SUPPORT
1 6 PINNED
LOAD 1
JOINT LOAD
2 FX 70
3 FX 45
PERFORM ANALYSIS
CHANGE
MEMBER TENSION
6 TO 9
LOAD 2
JOINT LOAD
4 FX -45
5 FX -70
PERFORM ANALYSIS
CHANGE
LOAD 3
REPEAT LOAD
1 1.0 2 1.0
PERFORM ANALYSIS
CHANGE
LOAD LIST 1 2 3
PRINT ANALYSIS RESULTS
FINI

STAAD Output File

                                                                  PAGE NO.    1
             ****************************************************        
             *                                                  *        
             *           STAAD.Pro CONNECT Edition              *        
             *           Version  22.04.00.**                   *        
             *           Proprietary Program of                 *        
             *           Bentley Systems, Inc.                  *        
             *           Date=    APR 21, 2020                  *        
             *           Time=    15:40:49                      *        
             *                                                  *        
             *  Licensed to: Bentley Systems Inc                *        
             ****************************************************        
     1. STAAD PLANE EXAMPLE FOR TENSION-ONLY MEMBERS
INPUT FILE: UK-21 Analysis of a Structure with Tension-Only Members.STD
     2. UNIT METER KNS
     3. SET NL 3
     4. JOINT COORDINATES
     5. 1 0 0 ; 2 0 3.5 ; 3 0 7.0 ; 4 5.25 7.0 ; 5 5.25 3.5 ; 6 5.25 0
     6. MEMBER INCIDENCES
     7. 1 1 2 5
     8. 6 1 5 ; 7 2 6 ; 8 2 4 ; 9 3 5 ; 10 2 5
     9. MEMBER TENSION
    10. 6 TO 9
    11. MEMBER PROPERTY BRITISH
    12. 1 TO 10 TABLE ST UC152X152X30
    13. UNIT MMS
    14. DEFINE MATERIAL START
    15. ISOTROPIC STEEL
    16. E 210
    17. POISSON 0.3
    18. DENSITY 7.6977E-008
    19. ALPHA 6E-006
    20. DAMP 0.03
    21. TYPE STEEL
    22. STRENGTH FY 0.24821 FU 0.399894 RY 1.5 RT 1.2
    23. END DEFINE MATERIAL
    24. CONSTANTS
    25. MATERIAL STEEL ALL
    26. SUPPORT
    27. 1 6 PINNED
    28. LOAD 1
    29. JOINT LOAD
    30. 2 FX 70
    31. 3 FX 45
    32. PERFORM ANALYSIS
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    2
            P R O B L E M   S T A T I S T I C S
            -----------------------------------
     NUMBER OF JOINTS          6  NUMBER OF MEMBERS      10
     NUMBER OF PLATES          0  NUMBER OF SOLIDS        0
     NUMBER OF SURFACES        0  NUMBER OF SUPPORTS      2
           Using 64-bit analysis engine.
           SOLVER USED IS THE IN-CORE ADVANCED MATH SOLVER
   TOTAL      PRIMARY LOAD CASES =     1, TOTAL DEGREES OF FREEDOM =      14
   TOTAL LOAD COMBINATION  CASES =     0  SO FAR.
*** LOAD CASE     1 -- START ITERATION NO.   2
  **NOTE-Tension/Compression converged after  2 iterations, Case=    1
    33. CHANGE
    34. MEMBER TENSION
    35. 6 TO 9
    36. LOAD 2
    37. JOINT LOAD
    38. 4 FX -45
    39. 5 FX -70
    40. PERFORM ANALYSIS
*** LOAD CASE     2 -- START ITERATION NO.   2
  **NOTE-Tension/Compression converged after  2 iterations, Case=    2
    41. CHANGE
    42. LOAD 3
    43. REPEAT LOAD
    44. 1 1.0 2 1.0
    45. PERFORM ANALYSIS
*** LOAD CASE     3 -- START ITERATION NO.   2
  **NOTE-Tension/Compression converged after  2 iterations, Case=    3
    46. CHANGE
    47. LOAD LIST 1 2 3
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    3
    48. PRINT ANALYSIS RESULTS
  ANALYSIS RESULTS                    
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    4
   JOINT DISPLACEMENT (CM   RADIANS)    STRUCTURE TYPE = PLANE
   ------------------
 JOINT  LOAD   X-TRANS   Y-TRANS   Z-TRANS   X-ROTAN   Y-ROTAN   Z-ROTAN
      1    1     0.0000    0.0000    0.0000    0.0000    0.0000   -0.0008
           2     0.0000    0.0000    0.0000    0.0000    0.0000    0.0005
           3     0.0000    0.0000    0.0000    0.0000    0.0000   -0.0001
      2    1     0.2355    0.0132    0.0000    0.0000    0.0000   -0.0004
           2    -0.1609   -0.0464    0.0000    0.0000    0.0000    0.0004
           3     0.0228    0.0000    0.0000    0.0000    0.0000   -0.0000
      3    1     0.3633    0.0133    0.0000    0.0000    0.0000   -0.0002
           2    -0.3341   -0.0594    0.0000    0.0000    0.0000    0.0004
           3     0.0147    0.0000    0.0000    0.0000    0.0000    0.0000
      4    1     0.3341   -0.0594    0.0000    0.0000    0.0000   -0.0004
           2    -0.3633    0.0133    0.0000    0.0000    0.0000    0.0002
           3    -0.0147    0.0000    0.0000    0.0000    0.0000   -0.0000
      5    1     0.1609   -0.0464    0.0000    0.0000    0.0000   -0.0004
           2    -0.2355    0.0132    0.0000    0.0000    0.0000    0.0004
           3    -0.0228    0.0000    0.0000    0.0000    0.0000    0.0000
      6    1     0.0000    0.0000    0.0000    0.0000    0.0000   -0.0005
           2     0.0000    0.0000    0.0000    0.0000    0.0000    0.0008
           3     0.0000    0.0000    0.0000    0.0000    0.0000    0.0001
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    5
   SUPPORT REACTIONS -UNIT KNS  MMS     STRUCTURE TYPE = PLANE
   -----------------
 JOINT  LOAD   FORCE-X   FORCE-Y   FORCE-Z     MOM-X     MOM-Y     MOM Z
      1    1   -114.92   -106.67      0.00      0.00      0.00      0.00
           2      0.08    106.67      0.00      0.00      0.00      0.00
           3     -0.05      0.00      0.00      0.00      0.00      0.00
      6    1     -0.08    106.67      0.00      0.00      0.00      0.00
           2    114.92   -106.67      0.00      0.00      0.00      0.00
           3      0.05      0.00      0.00      0.00      0.00      0.00
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    6
   MEMBER END FORCES    STRUCTURE TYPE = PLANE
   -----------------
   ALL UNITS ARE -- KNS  MMS      (LOCAL )
  MEMBER  LOAD  JT     AXIAL   SHEAR-Y  SHEAR-Z   TORSION     MOM-Y      MOM-Z
      1    1     1    -30.23      0.26     0.00      0.00      0.00       0.00
                 2     30.23     -0.26     0.00      0.00      0.00     894.16
           2     1    106.67     -0.08     0.00      0.00      0.00       0.00
                 2   -106.67      0.08     0.00      0.00      0.00    -294.48
           3     1     -0.00      0.05     0.00      0.00      0.00      -0.00
                 2      0.00     -0.05     0.00      0.00      0.00     158.18
      2    1     2     -0.25      0.21     0.00      0.00      0.00     200.03
                 3      0.25     -0.21     0.00      0.00      0.00     545.92
           2     2     29.82     -0.44     0.00      0.00      0.00    -770.68
                 3    -29.82      0.44     0.00      0.00      0.00    -756.76
           3     2     -0.00     -0.05     0.00      0.00      0.00    -137.99
                 3      0.00      0.05     0.00      0.00      0.00     -43.08
      3    1     3     44.79     -0.25     0.00      0.00      0.00    -545.92
                 4    -44.79      0.25     0.00      0.00      0.00    -756.76
           2     3     44.79      0.25     0.00      0.00      0.00     756.76
                 4    -44.79     -0.25     0.00      0.00      0.00     545.92
           3     3     45.05     -0.00     0.00      0.00      0.00      43.08
                 4    -45.05      0.00     0.00      0.00      0.00     -43.08
      4    1     4     29.82      0.44     0.00      0.00      0.00     756.76
                 5    -29.82     -0.44     0.00      0.00      0.00     770.68
           2     4     -0.25     -0.21     0.00      0.00      0.00    -545.92
                 5      0.25      0.21     0.00      0.00      0.00    -200.03
           3     4      0.00      0.05     0.00      0.00      0.00      43.08
                 5     -0.00     -0.05     0.00      0.00      0.00     137.99
      5    1     5    106.67      0.08     0.00      0.00      0.00     294.48
                 6   -106.67     -0.08     0.00      0.00      0.00       0.00
           2     5    -30.23     -0.26     0.00      0.00      0.00    -894.16
                 6     30.23      0.26     0.00      0.00      0.00       0.00
           3     5      0.00     -0.05     0.00      0.00      0.00    -158.18
                 6     -0.00      0.05     0.00      0.00      0.00       0.00
      6    1     1   -137.80      0.00     0.00      0.00      0.00       0.00
                 5    137.80      0.00     0.00      0.00      0.00       0.00
           2     1      0.00      0.00     0.00      0.00      0.00       0.00
                 5      0.00      0.00     0.00      0.00      0.00       0.00
           3     1      0.00      0.00     0.00      0.00      0.00       0.00
                 5      0.00      0.00     0.00      0.00      0.00       0.00
      7    1     2      0.00      0.00     0.00      0.00      0.00       0.00
                 6      0.00      0.00     0.00      0.00      0.00       0.00
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    7
   MEMBER END FORCES    STRUCTURE TYPE = PLANE
   -----------------
   ALL UNITS ARE -- KNS  MMS      (LOCAL )
  MEMBER  LOAD  JT     AXIAL   SHEAR-Y  SHEAR-Z   TORSION     MOM-Y      MOM-Z
           2     2   -137.80      0.00     0.00      0.00      0.00       0.00
                 6    137.80      0.00     0.00      0.00      0.00       0.00
           3     2      0.00      0.00     0.00      0.00      0.00       0.00
                 6      0.00      0.00     0.00      0.00      0.00       0.00
      8    1     2    -53.30      0.00     0.00      0.00      0.00       0.00
                 4     53.30      0.00     0.00      0.00      0.00       0.00
           2     2      0.00      0.00     0.00      0.00      0.00       0.00
                 4      0.00      0.00     0.00      0.00      0.00       0.00
           3     2      0.00      0.00     0.00      0.00      0.00       0.00
                 4      0.00      0.00     0.00      0.00      0.00       0.00
      9    1     3      0.00      0.00     0.00      0.00      0.00       0.00
                 5      0.00      0.00     0.00      0.00      0.00       0.00
           2     3    -53.30      0.00     0.00      0.00      0.00       0.00
                 5     53.30      0.00     0.00      0.00      0.00       0.00
           3     3      0.00      0.00     0.00      0.00      0.00       0.00
                 5      0.00      0.00     0.00      0.00      0.00       0.00
     10    1     2    114.31     -0.41     0.00      0.00      0.00   -1094.19
                 5   -114.31      0.41     0.00      0.00      0.00   -1065.16
           2     2    114.31      0.41     0.00      0.00      0.00    1065.16
                 5   -114.31     -0.41     0.00      0.00      0.00    1094.19
           3     2     69.90     -0.00     0.00      0.00      0.00     -20.19
                 5    -69.90      0.00     0.00      0.00      0.00      20.19
   ************** END OF LATEST ANALYSIS RESULT **************
    49. FINI
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    8
             *********** END OF THE STAAD.Pro RUN ***********         
               **** DATE= APR 21,2020   TIME= 15:40:49 ****
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