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EX. US-6 Prestress and Poststress Loading

This is an example of prestress loading in a plane frame structure.

It covers two situations:
  1. From the member on which it is applied, the prestressing effect is transmitted to the rest of the structure through the connecting members (known in the program as PRESTRESS load).
  2. The prestressing effect is experienced by the member(s) alone and not transmitted to the rest of the structure (known in the program as POSTSTRESS load).

This problem is installed with the program by default to C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\Sample Models\US\US-6 Prestress and Poststress Loading.STD when you install the program.

Example Problem No. 6

Where:

  • L1 = 15 ft
  • L2 = 20 ft
  • L3 = 40 ft

Actual input is shown in bold lettering followed by explanation.

    STAAD PLANE FRAME WITH PRESTRESSING LOAD

Every input has to start with the term STAAD. The term PLANE signifies that the structure is a plane frame structure and the geometry is defined through X and Y axes.

    UNIT KIP FT 

Defines the input units for the data that follows.

    JOINT COORD 
    1  0.  0.  ;  2  40.  0.  ;  3  0.  20.  ;  4  40.  20.  
    5  0.  35.  ;  6  40.  35.  ;  7  0.  50.  ;  8  40.  50.

Joint number followed by X and Y coordinates are provided above. Since this is a plane structure, the Z coordinates need not be provided.

Note: Semicolons (;) are used as line separators to allow for input of multiple sets of data on one line.
    MEMBER INCIDENCE
    1 1 3 ; 2 3 5 ; 3 5 7 ; 4 2 4 ; 5 4 6
    6 6 8 ; 7 3 4 ; 8 5 6 ; 9 7 8

Defines the members by the joints to which they are connected.

    SUPPORT 
    1 2 FIXED 

The supports at joints 1 and 2 are defined to be fixed supports.

    MEMB PROP 
    1 TO 9 PRI AX 2.2 IZ 1.0

Member properties are provided using the PRI (prismatic) attribute. Values of area (AX) and moment of inertia about the major axis (IZ) are provided.

    UNIT INCH
    DEFINE MATERIAL START
    ISOTROPIC CONCRETE
    E 3000.
    POISSON 0.17
    DENSITY 8.7e-005
    ALPHA 5e-006
    DAMP 0.05
    G 1346.15
    TYPE CONCRETE
    STRENGTH FCU 4
    END DEFINE MATERIAL
    CONSTANTS
    MATERIAL CONCRETE ALL

The DEFINE MATERIAL command is used to specify material properities and the CONSTANT command is used to assign the material to all members. Length unit is changed from FT to INCH to facilitate the input.

    LOADING 1 PRESTRESSING LOAD 
    MEMBER PRESTRESS
    7 8 FORCE 300. ES 3. EM -12. EE 3. 

Load case 1 is initiated along with an accompanying title. Load 1 contains PRESTRESS load. Members 7 and 8 have a cable force of 300 kips. The location of the cable at the start (ES) and end (EE) is 3 inches above the center of gravity while at the middle (EM) it is 12 inches below the c.g. The assumptions and facts associated with this type of loading are explained in G.15.5 Prestress and Poststress Member Load.

    LOADING 2 POSTSTRESSING LOAD 
    MEMBER POSTSTRESS
    7 8 FORCE 300. ES 3. EM -12. EE 3. 

Load case 2 is initiated along with an accompanying title. Load 2 is a POSTSTRESS load. Members 7 and 8 have cable force of 300 kips. The location of the cable is the same as in load case 1. For a difference between PRESTRESS loading and POSTSTRESS loading, as well as additional information about both types of loads, please refer to G.15.5 Prestress and Poststress Member Load.

    PERFORM ANALYSIS

This command instructs the program to perform the analysis.

    UNIT FT
    PRINT ANALYSIS RESULT

The preceding command is an instruction to write joint displacements, support reactions and member forces in the output file. The preceding line causes the results to be written in the length unit of feet.

    FINISH

This command terminates the STAAD run.

Input File

STAAD PLANE  FRAME WITH PRESTRESSING LOAD
UNIT KIP FT
JOINT COORD
1 0. 0. ; 2 40. 0. ; 3 0. 20. ; 4 40. 20.
5 0. 35. ; 6 40. 35. ; 7 0. 50. ; 8 40. 50.
MEMBER INCIDENCE
1 1 3 ; 2 3 5 ; 3 5 7 ; 4 2 4 ; 5 4 6
6 6 8 ; 7 3 4 ; 8 5 6 ; 9 7 8
SUPPORT
1 2 FIXED
MEMB PROP
1 TO 9 PRI AX 2.2 IZ 1.0
UNIT INCH
DEFINE MATERIAL START
ISOTROPIC CONCRETE
E 3000.
POISSON 0.17
DENSITY 8.7e-005
ALPHA 5e-006
DAMP 0.05
G 1346.15
TYPE CONCRETE
STRENGTH FCU 4
END DEFINE MATERIAL
CONSTANTS
MATERIAL CONCRETE ALL
LOADING 1 PRESTRESSING LOAD
MEMBER PRESTRESS
7 8 FORCE 300. ES 3. EM -12. EE 3.
LOADING 2 POSTSTRESSING LOAD
MEMBER POSTSTRESS
7 8 FORCE 300. ES 3. EM -12. EE 3.
PERFORM ANALYSIS
UNIT FT
PRINT ANALYSIS RESULT
FINISH

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=    15:42:40                      *        
             *                                                  *        
             *  Licensed to: Bentley Systems Inc                *        
             ****************************************************        
     1. STAAD PLANE  FRAME WITH PRESTRESSING LOAD
INPUT FILE: US-6 Prestress and Poststress Loading.STD
     2. UNIT KIP FT
     3. JOINT COORD
     4. 1 0. 0. ; 2 40. 0. ; 3 0. 20. ; 4 40. 20.
     5. 5 0. 35. ; 6 40. 35. ; 7 0. 50. ; 8 40. 50.
     6. MEMBER INCIDENCE
     7. 1 1 3 ; 2 3 5 ; 3 5 7 ; 4 2 4 ; 5 4 6
     8. 6 6 8 ; 7 3 4 ; 8 5 6 ; 9 7 8
     9. SUPPORT
    10. 1 2 FIXED
    11. MEMB PROP
    12. 1 TO 9 PRI AX 2.2 IZ 1.0
    13. UNIT INCH
    14. DEFINE MATERIAL START
    15. ISOTROPIC CONCRETE
    16. E 3000.
    17. POISSON 0.17
    18. DENSITY 8.7E-005
    19. ALPHA 5E-006
    20. DAMP 0.05
    21. G 1346.15
    22. TYPE CONCRETE
    23. STRENGTH FCU 4
    24. END DEFINE MATERIAL
    25. CONSTANTS
    26. MATERIAL CONCRETE ALL
    27. LOADING 1 PRESTRESSING LOAD
    28. MEMBER PRESTRESS
    29. 7 8 FORCE 300. ES 3. EM -12. EE 3.
    30. LOADING 2 POSTSTRESSING LOAD
    31. MEMBER POSTSTRESS
    32. 7 8 FORCE 300. ES 3. EM -12. EE 3.
    33. PERFORM ANALYSIS
      FRAME WITH PRESTRESSING LOAD                             -- PAGE NO.    2
            P R O B L E M   S T A T I S T I C S
            -----------------------------------
     NUMBER OF JOINTS          8  NUMBER OF MEMBERS       9
     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 =     2, TOTAL DEGREES OF FREEDOM =      18
   TOTAL LOAD COMBINATION  CASES =     0  SO FAR.
    34. UNIT FT
    35. PRINT ANALYSIS RESULT
  ANALYSIS RESULT                     
      FRAME WITH PRESTRESSING LOAD                             -- PAGE NO.    3
   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   0.00000
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
      2    1    0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
      3    1    0.07698   0.00000   0.00000   0.00000   0.00000   0.00039
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
      4    1   -0.07698   0.00000   0.00000   0.00000   0.00000  -0.00039
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
      5    1    0.07224   0.00000   0.00000   0.00000   0.00000   0.00087
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
      6    1   -0.07224   0.00000   0.00000   0.00000   0.00000  -0.00087
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
      7    1   -0.00059   0.00000   0.00000   0.00000   0.00000   0.00015
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
      8    1    0.00059   0.00000   0.00000   0.00000   0.00000  -0.00015
           2    0.00000   0.00000   0.00000   0.00000   0.00000   0.00000
      FRAME WITH PRESTRESSING LOAD                             -- PAGE NO.    4
   SUPPORT REACTIONS -UNIT KIP  FEET    STRUCTURE TYPE = PLANE
   -----------------
 JOINT  LOAD   FORCE-X   FORCE-Y   FORCE-Z     MOM-X     MOM-Y     MOM Z
      1    1     -6.71      0.00      0.00      0.00      0.00     58.62
           2      0.00      0.00      0.00      0.00      0.00      0.00
      2    1      6.71      0.00      0.00      0.00      0.00    -58.62
           2      0.00      0.00      0.00      0.00      0.00      0.00
      FRAME WITH PRESTRESSING LOAD                             -- PAGE NO.    5
   MEMBER END FORCES    STRUCTURE TYPE = PLANE
   -----------------
   ALL UNITS ARE -- KIP  FEET     (LOCAL )
  MEMBER  LOAD  JT     AXIAL   SHEAR-Y  SHEAR-Z   TORSION     MOM-Y      MOM-Z
      1    1     1      0.00      6.71     0.00      0.00      0.00      58.62
                 3     -0.00     -6.71     0.00      0.00      0.00      75.67
           2     1      0.00      0.00     0.00      0.00      0.00       0.00
                 3      0.00      0.00     0.00      0.00      0.00       0.00
      2    1     3      0.00     13.92     0.00      0.00      0.00      90.81
                 5     -0.00    -13.92     0.00      0.00      0.00     117.98
           2     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
      3    1     5      0.00      2.34     0.00      0.00      0.00      38.31
                 7     -0.00     -2.34     0.00      0.00      0.00      -3.16
           2     5      0.00      0.00     0.00      0.00      0.00       0.00
                 7      0.00      0.00     0.00      0.00      0.00       0.00
      4    1     2     -0.00     -6.71     0.00      0.00      0.00     -58.62
                 4      0.00      6.71     0.00      0.00      0.00     -75.67
           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
      5    1     4     -0.00    -13.92     0.00      0.00      0.00     -90.81
                 6      0.00     13.92     0.00      0.00      0.00    -117.98
           2     4      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
      6    1     6     -0.00     -2.34     0.00      0.00      0.00     -38.31
                 8      0.00      2.34     0.00      0.00      0.00       3.16
           2     6      0.00      0.00     0.00      0.00      0.00       0.00
                 8      0.00      0.00     0.00      0.00      0.00       0.00
      7    1     3    304.85    -37.50     0.00      0.00      0.00    -241.48
                 4   -304.85    -37.50     0.00      0.00      0.00     241.48
           2     3    297.65    -37.50     0.00      0.00      0.00     -75.00
                 4   -297.65    -37.50     0.00      0.00      0.00      75.00
      8    1     5    286.07    -37.50     0.00      0.00      0.00    -231.29
                 6   -286.07    -37.50     0.00      0.00      0.00     231.29
           2     5    297.65    -37.50     0.00      0.00      0.00     -75.00
                 6   -297.65    -37.50     0.00      0.00      0.00      75.00
      9    1     7     -2.34      0.00     0.00      0.00      0.00       3.16
                 8      2.34     -0.00     0.00      0.00      0.00      -3.16
      FRAME WITH PRESTRESSING LOAD                             -- PAGE NO.    6
   MEMBER END FORCES    STRUCTURE TYPE = PLANE
   -----------------
   ALL UNITS ARE -- KIP  FEET     (LOCAL )
  MEMBER  LOAD  JT     AXIAL   SHEAR-Y  SHEAR-Z   TORSION     MOM-Y      MOM-Z
           2     7      0.00      0.00     0.00      0.00      0.00       0.00
                 8      0.00      0.00     0.00      0.00      0.00       0.00
   ************** END OF LATEST ANALYSIS RESULT **************
    36. FINISH
             *********** END OF THE STAAD.Pro RUN ***********         
               **** DATE= APR 21,2020   TIME= 15:42:40 ****
      FRAME WITH PRESTRESSING LOAD                             -- PAGE NO.    7
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