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EX. US-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\US\US-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 = 15 ft, H = 10 ft
  • Load case 1: P1 = 10 kips & P2 = 15 kips
  • Load case 2: P3 = -10 kips & P4 = -15 kips
    STAAD PLANE EXAMPLE FOR TENSION-ONLY MEMBERS

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

    UNIT FEET KIP

Units for the commands to follow are defined above.

    JOINT COORDINATES
    1 0 0 ; 2 0 10 ; 3 0 20 ; 4 15 20 ; 5 15 10 ; 6 15 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 AMERICAN
    1 TO 10 TA ST W12X26

All members have been assigned a WIDE FLANGE section from the built in American table.

    UNIT INCH
    DEFINE MATERIAL START
    ISOTROPIC STEEL
    E 29000
    POISSON 0.3
    DENSITY 283e-006
    ALPHA 6e-006
    DAMP 0.03
    TYPE STEEL
    STRENGTH FY 36 FU 58 RY 1.5 RT 1.2
    END DEFINE MATERIAL
    CONSTANT
    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 feet to inch to facilitate the input of these values.

    SUPPORT
    1 6 PINNED

The supports are defined above.

    MEMBER TENSION
    6 TO 9

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

    LOAD 1
    JOINT LOAD
    2 FX 15
    3 FX 10

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

    LOAD 2
    JOINT LOAD
    4 FX -10
    5 FX -15

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 FEET KIP
SET NL 3
JOINT COORDINATES
1 0 0 ; 2 0 10 ; 3 0 20 ; 4 15 20 ; 5 15 10 ; 6 15 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 AMERICAN
1 TO 10 TA ST W12X26
UNIT INCH
DEFINE MATERIAL START
ISOTROPIC STEEL
E 29000.0
POISSON 0.3
DENSITY 283e-006
ALPHA 6e-006
DAMP 0.03
TYPE STEEL
STRENGTH FY 36 FU 58 RY 1.5 RT 1.2
END DEFINE MATERIAL
CONSTANT
MATERIAL STEEL ALL
SUPPORT
1 PINNED
6 PINNED
LOAD 1
JOINT LOAD
2 FX 15
3 FX 10
PERFORM ANALYSIS
CHANGE
MEMBER TENSION
6 TO 9
LOAD 2
JOINT LOAD
4 FX -10
5 FX -15
PERFORM ANALYSIS
CHANGE
MEMBER TENSION
6 TO 9
LOAD 3
REPEAT LOAD
1 1.0 2 1.0
PERFORM ANALYSIS
CHANGE
LOAD LIST ALL
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=    15:42: 7                      *        
             *                                                  *        
             *  Licensed to: Bentley Systems Inc                *        
             ****************************************************        
     1. STAAD PLANE EXAMPLE FOR TENSION-ONLY MEMBERS
INPUT FILE: US-21 Analysis of a Structure with Tension-Only Members.STD
     2. UNIT FEET KIP
     3. SET NL 3
     4. JOINT COORDINATES
     5. 1 0 0 ; 2 0 10 ; 3 0 20 ; 4 15 20 ; 5 15 10 ; 6 15 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 AMERICAN
    12. 1 TO 10 TA ST W12X26
    13. UNIT INCH
    14. DEFINE MATERIAL START
    15. ISOTROPIC STEEL
    16. E 29000.0
    17. POISSON 0.3
    18. DENSITY 283E-006
    19. ALPHA 6E-006
    20. DAMP 0.03
    21. TYPE STEEL
    22. STRENGTH FY 36 FU 58 RY 1.5 RT 1.2
    23. END DEFINE MATERIAL
    24. CONSTANT
    25. MATERIAL STEEL ALL
    26. SUPPORT
    27. 1 PINNED
    28. 6 PINNED
    29. LOAD 1
    30. JOINT LOAD
    31. 2 FX 15
    32. 3 FX 10
    33. 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
    34. CHANGE
    35. MEMBER TENSION
    36. 6 TO 9
    37. LOAD 2
    38. JOINT LOAD
    39. 4 FX -10
    40. 5 FX -15
    41. PERFORM ANALYSIS
*** LOAD CASE     2 -- START ITERATION NO.   2
  **NOTE-Tension/Compression converged after  2 iterations, Case=    2
    42. CHANGE
    43. MEMBER TENSION
    44. 6 TO 9
    45. LOAD 3
    46. REPEAT LOAD
    47. 1 1.0 2 1.0
    48. PERFORM ANALYSIS
*** LOAD CASE     3 -- START ITERATION NO.   2
  **NOTE-Tension/Compression converged after  2 iterations, Case=    3
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    3
    49. CHANGE
    50. LOAD LIST ALL
    51. PRINT ANALYSIS RESULTS
  ANALYSIS RESULTS                    
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    4
   JOINT DISPLACEMENT (INCH RADIANS)    STRUCTURE TYPE = PLANE
   ------------------
 JOINT  LOAD   X-TRANS   Y-TRANS   Z-TRANS   X-ROTAN   Y-ROTAN   Z-ROTAN
      1    1    0.00000   0.00000   0.00000   0.00000   0.00000  -0.00062
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00039
           3    0.00000   0.00000   0.00000   0.00000   0.00000  -0.00007
      2    1    0.06285   0.00373   0.00000   0.00000   0.00000  -0.00030
           2   -0.04313  -0.01262   0.00000   0.00000   0.00000   0.00028
           3    0.00605   0.00000   0.00000   0.00000   0.00000  -0.00001
      3    1    0.09724   0.00387   0.00000   0.00000   0.00000  -0.00018
           2   -0.08929  -0.01613   0.00000   0.00000   0.00000   0.00029
           3    0.00408   0.00000   0.00000   0.00000   0.00000   0.00002
      4    1    0.08929  -0.01613   0.00000   0.00000   0.00000  -0.00029
           2   -0.09724   0.00387   0.00000   0.00000   0.00000   0.00018
           3   -0.00408   0.00000   0.00000   0.00000   0.00000  -0.00002
      5    1    0.04313  -0.01262   0.00000   0.00000   0.00000  -0.00028
           2   -0.06285   0.00373   0.00000   0.00000   0.00000   0.00030
           3   -0.00605   0.00000   0.00000   0.00000   0.00000   0.00001
      6    1    0.00000   0.00000   0.00000   0.00000   0.00000  -0.00039
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00062
           3    0.00000   0.00000   0.00000   0.00000   0.00000   0.00007
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    5
   SUPPORT REACTIONS -UNIT KIP  INCH    STRUCTURE TYPE = PLANE
   -----------------
 JOINT  LOAD   FORCE-X   FORCE-Y   FORCE-Z     MOM-X     MOM-Y     MOM Z
      1    1    -24.91    -23.33      0.00      0.00      0.00      0.00
           2      0.09     23.33      0.00      0.00      0.00      0.00
           3     -0.05      0.00      0.00      0.00      0.00      0.00
      6    1     -0.09     23.33      0.00      0.00      0.00      0.00
           2     24.91    -23.33      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 -- KIP  INCH     (LOCAL )
  MEMBER  LOAD  JT     AXIAL   SHEAR-Y  SHEAR-Z   TORSION     MOM-Y      MOM-Z
      1    1     1     -6.90      0.26     0.00      0.00      0.00       0.00
                 2      6.90     -0.26     0.00      0.00      0.00      31.66
           2     1     23.33     -0.09     0.00      0.00      0.00      -0.00
                 2    -23.33      0.09     0.00      0.00      0.00     -10.81
           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       5.46
      2    1     2     -0.24      0.20     0.00      0.00      0.00       6.07
                 3      0.24     -0.20     0.00      0.00      0.00      18.42
           2     2      6.49     -0.43     0.00      0.00      0.00     -25.74
                 3     -6.49      0.43     0.00      0.00      0.00     -25.59
           3     2      0.00     -0.05     0.00      0.00      0.00      -4.66
                 3     -0.00      0.05     0.00      0.00      0.00      -1.39
      3    1     3      9.80     -0.24     0.00      0.00      0.00     -18.42
                 4     -9.80      0.24     0.00      0.00      0.00     -25.59
           2     3      9.80      0.24     0.00      0.00      0.00      25.59
                 4     -9.80     -0.24     0.00      0.00      0.00      18.42
           3     3     10.05      0.00     0.00      0.00      0.00       1.39
                 4    -10.05     -0.00     0.00      0.00      0.00      -1.39
      4    1     4      6.49      0.43     0.00      0.00      0.00      25.59
                 5     -6.49     -0.43     0.00      0.00      0.00      25.74
           2     4     -0.24     -0.20     0.00      0.00      0.00     -18.42
                 5      0.24      0.20     0.00      0.00      0.00      -6.07
           3     4     -0.00      0.05     0.00      0.00      0.00       1.39
                 5      0.00     -0.05     0.00      0.00      0.00       4.66
      5    1     5     23.33      0.09     0.00      0.00      0.00      10.81
                 6    -23.33     -0.09     0.00      0.00      0.00       0.00
           2     5     -6.90     -0.26     0.00      0.00      0.00     -31.66
                 6      6.90      0.26     0.00      0.00      0.00       0.00
           3     5     -0.00     -0.05     0.00      0.00      0.00      -5.46
                 6      0.00      0.05     0.00      0.00      0.00       0.00
      6    1     1    -29.62      0.00     0.00      0.00      0.00       0.00
                 5     29.62      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 -- KIP  INCH     (LOCAL )
  MEMBER  LOAD  JT     AXIAL   SHEAR-Y  SHEAR-Z   TORSION     MOM-Y      MOM-Z
           2     2    -29.62      0.00     0.00      0.00      0.00       0.00
                 6     29.62      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    -11.26      0.00     0.00      0.00      0.00       0.00
                 4     11.26      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    -11.26      0.00     0.00      0.00      0.00       0.00
                 5     11.26      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     24.31     -0.41     0.00      0.00      0.00     -37.72
                 5    -24.31      0.41     0.00      0.00      0.00     -36.55
           2     2     24.31      0.41     0.00      0.00      0.00      36.55
                 5    -24.31     -0.41     0.00      0.00      0.00      37.72
           3     2     14.90      0.00     0.00      0.00      0.00      -0.79
                 5    -14.90     -0.00     0.00      0.00      0.00       0.79
   ************** END OF LATEST ANALYSIS RESULT **************
    52. FINI
      EXAMPLE FOR TENSION-ONLY MEMBERS                         -- PAGE NO.    8
             *********** END OF THE STAAD.Pro RUN ***********         
               **** DATE= APR 21,2020   TIME= 15:42: 7 ****
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