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EX. US-12 Moving Load Generation on a Bridge Deck

This example demonstrates generation of load cases for the type of loading known as a moving load. This type of loading occurs classically when the load-causing units move on the structure, as in the case of trucks on a bridge deck. The mobile loads are discretized into several individual immobile load cases at discrete positions. During this process, enormous number of load cases may be created resulting in plenty of output to be sorted. To avoid looking into a lot of output, the maximum force envelope is requested for a few specific members.

This problem is installed with the program by default to C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\Sample Models\US\US-12 Moving Load Generation on a Bridge Deck.STD when you install the program.

Example Problem No. 12

Where:

  • L1 = 30 ft
  • L2 = 5 ft

Actual input is shown in bold lettering followed by explanation.

    STAAD FLOOR A SIMPLE BRIDGE DECK

Every input has to start with the term STAAD. The word FLOOR signifies that the structure is a floor structure and the geometry is defined through X and Z axis.

    UNITS FEET KIPS

Defines the input units for the data that follows.

    JOINT COORDINATES
    1  0  0  0  6  25  0  0  
    R  5  0  0  30

Joint number followed by X, Y, and Z coordinates are provided above. Since this is a floor structure, the Y coordinates are all the same (in this case, zero). The first line generates joints 1 through 6. With the repeat (R) command, the coordinates of the next 30 joints are generated by repeating the pattern of the coordinates of the first 6 joints 5 times with X, Y and Z increments of 0,0, and 9 respectively.

    MEMBER INCIDENCES
    1 1 7 6
    7 1 2 11
    R A 4 11 6
    56 31 32 60

Defines the members by the joints to which they are connected. The fourth number indicates the final member number up to which they will be generated. Repeat all (abbreviated as R A) will create members by repeating the member incidence pattern of the previous 11 members. The number of repetitions to be carried out is provided after the R A command and the member increment and joint increment are defined as 11 and 6 respectively. The fifth line of input defines the member incidences for members 56 to 60.

    MEMBER PROPERTIES AMERICAN
    1 TO 60 TA ST W12X26

Member properties are assigned from the American AISC table for all members. The word ST stands for standard single section.

    SUPPORTS
    1 TO 6 31 TO 36 PINNED

Pinned supports are specified at the above joints. A pinned support is one which can resist only translational forces.

    UNITS 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 input units are changed from FT to INCH. The DEFINE MATERIAL command is used to specify material properties and the CONSTANT is used to assign the material to all members.

    UNIT FEET KIP
    DEFINE MOVING LOAD
    TYPE 1 LOAD  20.  20.  10.  DISTANCE  10.  5.  WIDTH  10.0

The characteristics of the vehicle are defined above in METER and KNS units. The above lines represent the first out of two sets of data required in moving load generation. The type number (1) is a label for identification of the load-causing unit, such as a truck. Three axles (20 20 10) are specified with the LOAD command. The spacing between the axles in the direction of movement (longitudinal direction) is specified after the DISTANCE command. WIDTH is the spacing in the transverse direction, that is, it is the distance between the 2 prongs of an axle of the truck.

    LOAD 1

Load case 1 is initiated.

    SELF Y -1.0

Selfweight of the structure acting in the negative (due to the factor -1.0) global Y direction is the only component of load case 1.

    LOAD GENERATION  10
    TYPE  1  7.5  0.  0.  ZI  10.

This constitutes the second of the two sets of data required for moving load generation. 10 load cases are generated using the Type 1 vehicle whose characteristics were described earlier. For the first of these load cases, the X, Y and Z location of the reference load (see TR.31.1 Definition of Moving Load System ) have been specified after the command TYPE 1. The Z Increment of 10ft denotes that the vehicle moves along the Z direction and the individual positions which are 10ft apart will be used to generate the remaining 9 load cases.

When defining a moving load in STAAD.Pro, the reference wheel is on the last axle. The first load case which is generated will be the one for which the first axle is just about to enter the bridge. The last load case should be the one for which the last axle is just about to exit the bridge. Thus, the total distance travelled by the reference load will be the length of the vehicle (distance from first axle to last axle) plus the span of the bridge. In this problem, that comes to

(10+5) + 150 = 165 feet.

This example uses 10 ft increments and generates 10 load cases.

However, if you want the vehicle to move forward in 15 feet increments (each 15 foot increment will create a discrete position of the truck on the bridge), it would required (165/15)+1 = 12 cases to be generated.

    PERFORM ANALYSIS PRINT LOAD

The above command instructs the program to proceed with the analysis and print the values and positions of all the generated load cases.

    PRINT MAXFORCE ENVELOP LIST 3 41 42

A maximum force envelope consisting of the highest forces for each degree of freedom on the listed members will be written into the output file.

    FINISH

This command terminates the STAAD run.

Input File

STAAD FLOOR A SIMPLE BRIDGE DECK
UNITS FEET KIPS
JOINT COORDINATES
1 0 0 0 6 25 0 0
R 5 0 0 30
MEMBER INCIDENCES
1 1 7 6
7 1 2 11
R A 4 11 6
56 31 32 60
MEMBER PROPERTIES AMERICAN
1 TO 60 TA ST W12X26
SUPPORTS
1 TO 6 31 TO 36 PINNED
UNITS 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
UNIT FEET KIP
DEFINE MOVING LOAD
TYPE 1 LOAD 20. 20. 10. DISTANCE 10. 5. WIDTH 10.
LOAD 1
SELF Y -1.0
LOAD GENERATION 10
TYPE 1 7.5 0. 0. ZI 10.
PERFORM ANALYSIS PRINT LOAD
PRINT MAXFORCE ENVELOP LIST 3 41 42
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=    15:41:42                      *        
             *                                                  *        
             *  Licensed to: Bentley Systems Inc                *        
             ****************************************************        
     1. STAAD FLOOR A SIMPLE BRIDGE DECK
INPUT FILE: US-12 Moving Load Generation on a Bridge Deck.STD
     2. UNITS FEET KIPS
     3. JOINT COORDINATES
     4. 1 0 0 0 6 25 0 0
     5. R 5 0 0 30
     6. MEMBER INCIDENCES
     7. 1 1 7 6
     8. 7 1 2 11
     9. R A 4 11 6
    10. 56 31 32 60
    11. MEMBER PROPERTIES AMERICAN
    12. 1 TO 60 TA ST W12X26
    13. SUPPORTS
    14. 1 TO 6 31 TO 36 PINNED
    15. UNITS INCH
    16. DEFINE MATERIAL START
    17. ISOTROPIC STEEL
    18. E 29000
    19. POISSON 0.3
    20. DENSITY 283E-006
    21. ALPHA 6E-006
    22. DAMP 0.03
    23. TYPE STEEL
    24. STRENGTH FY 36 FU 58 RY 1.5 RT 1.2
    25. END DEFINE MATERIAL
    26. CONSTANT
    27. MATERIAL STEEL ALL
    28. UNIT FEET KIP
    29. DEFINE MOVING LOAD
    30. TYPE 1 LOAD 20. 20. 10. DISTANCE 10. 5. WIDTH 10.
    31. LOAD 1
    32. SELF Y -1.0
    33. LOAD GENERATION 10
    34. TYPE 1 7.5 0. 0. ZI 10.
    35. PERFORM ANALYSIS PRINT LOAD
      A SIMPLE BRIDGE DECK                                     -- PAGE NO.    2
            P R O B L E M   S T A T I S T I C S
            -----------------------------------
     NUMBER OF JOINTS         36  NUMBER OF MEMBERS      60
     NUMBER OF PLATES          0  NUMBER OF SOLIDS        0
     NUMBER OF SURFACES        0  NUMBER OF SUPPORTS     12
           Using 64-bit analysis engine.
           SOLVER USED IS THE IN-CORE ADVANCED MATH SOLVER
   TOTAL      PRIMARY LOAD CASES =    11, TOTAL DEGREES OF FREEDOM =      96
   TOTAL LOAD COMBINATION  CASES =     0  SO FAR.
      A SIMPLE BRIDGE DECK                                     -- PAGE NO.    3
   LOADING     1                                                              
   -----------
       SELFWEIGHT  Y   -1.000
      ACTUAL WEIGHT OF THE STRUCTURE =      27.278 KIP 
   LOADING     2                                                              
   -----------
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
      8                           -20.0000 GY   2.50
     10                           -20.0000 GY   2.50
      3                           -10.0000 GY  10.00
      2                           -10.0000 GY  10.00
      5                           -10.0000 GY  10.00
      4                           -10.0000 GY  10.00
      3                            -5.0000 GY  15.00
      2                            -5.0000 GY  15.00
      5                            -5.0000 GY  15.00
      4                            -5.0000 GY  15.00
   LOADING     3                                                              
   -----------
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
      3                           -10.0000 GY  10.00
      2                           -10.0000 GY  10.00
      5                           -10.0000 GY  10.00
      4                           -10.0000 GY  10.00
      3                           -10.0000 GY  20.00
      2                           -10.0000 GY  20.00
      5                           -10.0000 GY  20.00
      4                           -10.0000 GY  20.00
      3                            -5.0000 GY  25.00
      2                            -5.0000 GY  25.00
      5                            -5.0000 GY  25.00
      4                            -5.0000 GY  25.00
   LOADING     4                                                              
   -----------
      A SIMPLE BRIDGE DECK                                     -- PAGE NO.    4
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
      3                           -10.0000 GY  20.00
      2                           -10.0000 GY  20.00
      5                           -10.0000 GY  20.00
      4                           -10.0000 GY  20.00
     19                           -20.0000 GY   2.50
     21                           -20.0000 GY   2.50
     14                            -5.0000 GY   5.00
     13                            -5.0000 GY   5.00
     16                            -5.0000 GY   5.00
     15                            -5.0000 GY   5.00
   LOADING     5                                                              
   -----------
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
     19                           -20.0000 GY   2.50
     21                           -20.0000 GY   2.50
     14                           -10.0000 GY  10.00
     13                           -10.0000 GY  10.00
     16                           -10.0000 GY  10.00
     15                           -10.0000 GY  10.00
     14                            -5.0000 GY  15.00
     13                            -5.0000 GY  15.00
     16                            -5.0000 GY  15.00
     15                            -5.0000 GY  15.00
   LOADING     6                                                              
   -----------
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
     14                           -10.0000 GY  10.00
     13                           -10.0000 GY  10.00
     16                           -10.0000 GY  10.00
     15                           -10.0000 GY  10.00
     14                           -10.0000 GY  20.00
     13                           -10.0000 GY  20.00
     16                           -10.0000 GY  20.00
     15                           -10.0000 GY  20.00
     14                            -5.0000 GY  25.00
     13                            -5.0000 GY  25.00
      A SIMPLE BRIDGE DECK                                     -- PAGE NO.    5
     16                            -5.0000 GY  25.00
     15                            -5.0000 GY  25.00
   LOADING     7                                                              
   -----------
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
     14                           -10.0000 GY  20.00
     13                           -10.0000 GY  20.00
     16                           -10.0000 GY  20.00
     15                           -10.0000 GY  20.00
     30                           -20.0000 GY   2.50
     32                           -20.0000 GY   2.50
     25                            -5.0000 GY   5.00
     24                            -5.0000 GY   5.00
     27                            -5.0000 GY   5.00
     26                            -5.0000 GY   5.00
   LOADING     8                                                              
   -----------
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
     30                           -20.0000 GY   2.50
     32                           -20.0000 GY   2.50
     25                           -10.0000 GY  10.00
     24                           -10.0000 GY  10.00
     27                           -10.0000 GY  10.00
     26                           -10.0000 GY  10.00
     25                            -5.0000 GY  15.00
     24                            -5.0000 GY  15.00
     27                            -5.0000 GY  15.00
     26                            -5.0000 GY  15.00
   LOADING     9                                                              
   -----------
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
     25                           -10.0000 GY  10.00
     24                           -10.0000 GY  10.00
     27                           -10.0000 GY  10.00
     26                           -10.0000 GY  10.00
      A SIMPLE BRIDGE DECK                                     -- PAGE NO.    6
     25                           -10.0000 GY  20.00
     24                           -10.0000 GY  20.00
     27                           -10.0000 GY  20.00
     26                           -10.0000 GY  20.00
     25                            -5.0000 GY  25.00
     24                            -5.0000 GY  25.00
     27                            -5.0000 GY  25.00
     26                            -5.0000 GY  25.00
   LOADING    10                                                              
   -----------
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
     25                           -10.0000 GY  20.00
     24                           -10.0000 GY  20.00
     27                           -10.0000 GY  20.00
     26                           -10.0000 GY  20.00
     41                           -20.0000 GY   2.50
     43                           -20.0000 GY   2.50
     36                            -5.0000 GY   5.00
     35                            -5.0000 GY   5.00
     38                            -5.0000 GY   5.00
     37                            -5.0000 GY   5.00
   LOADING    11                                                              
   -----------
   MEMBER LOAD - UNIT KIP  FEET
   MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
     41                           -20.0000 GY   2.50
     43                           -20.0000 GY   2.50
     36                           -10.0000 GY  10.00
     35                           -10.0000 GY  10.00
     38                           -10.0000 GY  10.00
     37                           -10.0000 GY  10.00
     36                            -5.0000 GY  15.00
     35                            -5.0000 GY  15.00
     38                            -5.0000 GY  15.00
     37                            -5.0000 GY  15.00
   ************ END OF DATA FROM INTERNAL STORAGE ************
    36. PRINT MAXFORCE ENVELOP LIST 3 41 42
  MAXFORCE ENVELOP  LIST     3        
      A SIMPLE BRIDGE DECK                                     -- PAGE NO.    7
         MEMBER FORCE ENVELOPE
         ---------------------
         ALL UNITS ARE KIP  FEET
   MAX AND MIN FORCE VALUES AMONGST ALL SECTION LOCATIONS
  MEMB          FY/    DIST  LD        MZ/    DIST  LD
                FZ     DIST  LD        MY     DIST  LD        FX     DIST  LD
     3 MAX     18.03   0.00    3       0.02   0.00    4
                0.00   0.00    1       0.00   0.00    1      0.00     0.00    1
       MIN     -6.97  27.50    3    -373.90  30.00    5
                0.00  30.00   11       0.00  30.00   11      0.00    30.00   11
    41 MAX     16.33   0.00   10       6.80   5.00    5
                0.00   0.00    1       0.00   0.00    1      0.00     0.00    1
       MIN     -4.08   5.00   11    -109.08   2.50   10
                0.00   5.00   11       0.00   5.00   11      0.00     5.00   11
    42 MAX      0.06   0.00    1       6.80   0.00    5
                0.00   0.00    1       0.00   0.00    1      0.00     0.00    1
       MIN     -0.06   5.00    1     -99.89   5.00   10
                0.00   5.00   11       0.00   5.00   11      0.00     5.00   11
   ********** END OF FORCE ENVELOPE FROM INTERNAL STORAGE **********
    37. FINISH
             *********** END OF THE STAAD.Pro RUN ***********         
               **** DATE= APR 21,2020   TIME= 15:41:43 ****
      A SIMPLE BRIDGE DECK                                     -- PAGE NO.    8
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