# 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
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
4 FX -45
5 FX -70```

Load case 2 is described above.

```    LOAD 3
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
2 FX 70
3 FX 45
PERFORM ANALYSIS
CHANGE
MEMBER TENSION
6 TO 9
4 FX -45
5 FX -70
PERFORM ANALYSIS
CHANGE
1 1.0 2 1.0
PERFORM ANALYSIS
CHANGE
PRINT ANALYSIS RESULTS
FINI
``````

```                                                                  PAGE NO.    1
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*                                                  *
*           Version  22.08.00.***                  *
*           Proprietary Program of                 *
*           Bentley Systems, Inc.                  *
*           Date=    OCT 19, 2021                  *
*           Time=    17:53:55                      *
*                                                  *
*  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
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
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
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= OCT 19,2021   TIME= 17:53:56 ****
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