# 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
2 FX 15
3 FX 10```

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

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

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 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
2 FX 15
3 FX 10
PERFORM ANALYSIS
CHANGE
MEMBER TENSION
6 TO 9
4 FX -10
5 FX -15
PERFORM ANALYSIS
CHANGE
MEMBER TENSION
6 TO 9
1 1.0 2 1.0
PERFORM ANALYSIS
CHANGE
PRINT ANALYSIS RESULTS
FINI
``````

```                                                                  PAGE NO.    1
****************************************************
*                                                  *
*           Version  22.08.00.***                  *
*           Proprietary Program of                 *
*           Bentley Systems, Inc.                  *
*           Date=    OCT 19, 2021                  *
*           Time=    17:55:14                      *
*                                                  *
*  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
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
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
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
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= OCT 19,2021   TIME= 17:55:15 ****
************************************************************