# EX. UK-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\UK\UK-12 Moving Load Generation on a Bridge Deck.STD when you install the program.

### Example Problem No. 12

Where:

• L1 = 9 m
• L2 = 1.5 m

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 METER KNS
```

Defines the input units for the data that follows.

```    JOINT COORDINATES
1 0 0 0 6 7.5 0 0
R 5 0 0 9.0
```

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 BRITISH
1 TO 60 TA ST UB305X165X40
```

Properties for all members are assigned from the British steel table. 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 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 0.25 FU 0.4 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 units of length are changed from METER to MMS.

```    UNIT METER KNS
TYPE 1 LOAD 90.0 90.0 45.0
DISTANCE 3.0 1.5 WIDTH 3.0
```

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 (90 90 45) 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
```

```    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 2.25 0. 0. ZI 3.0
```

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 3.0m denotes that the vehicle moves along the Z direction and the individual positions which are 3.0m 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

(3.0+1.5) + 45 = 49.5 m.

This example uses 3.0 m increments and generates 10 load cases.

However, if you want the vehicle to move forward in 4.5 m increments (each 4.5 m increment will create a discrete position of the truck on the bridge), it would required (49.5/4.5)+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 METER KNS
JOINT COORDINATES
1 0.0 0.0 0.0 6 7.5 0.0 0.0
R 5 0.0 0.0 9.0
MEMBER INCIDENCES
1 1 7 6
7 1 2 11
R A 4 11 6
56 31 32 60
MEMBER PROPERTIES BRITISH
1 TO 60 TA ST UB305X165X40
SUPPORTS
1 TO 6 31 TO 36 PINNED
UNITS 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 0.25 FU 0.4 RY 1.5 RT 1.2
END DEFINE MATERIAL
CONSTANTS
MATERIAL STEEL ALL
UNIT METER KNS
TYPE 1 LOAD 90.0 90.0 45.0 DISTANCE 3.0 1.5 WIDTH 3.0
SELF Y -1.0
TYPE 1 2.25 0. 0. ZI 3.0
PRINT MAXFORCE ENVELOP LIST 3 41 42
FINISH
``````

```                                                                  PAGE NO.    1
****************************************************
*                                                  *
*           Version  22.08.00.***                  *
*           Proprietary Program of                 *
*           Bentley Systems, Inc.                  *
*           Date=    OCT 19, 2021                  *
*           Time=    17:53:31                      *
*                                                  *
*  Licensed to: Bentley Systems Inc                *
****************************************************
1. STAAD FLOOR A SIMPLE BRIDGE DECK
INPUT FILE: UK-12 Moving Load Generation on a Bridge Deck.STD
2. UNITS METER KNS
3. JOINT COORDINATES
4. 1 0.0 0.0 0.0 6 7.5 0.0 0.0
5. R 5 0.0 0.0 9.0
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 BRITISH
12. 1 TO 60 TA ST UB305X165X40
13. SUPPORTS
14. 1 TO 6 31 TO 36 PINNED
15. UNITS MMS
16. DEFINE MATERIAL START
17. ISOTROPIC STEEL
18. E 210
19. POISSON 0.3
20. DENSITY 7.6977E-008
21. ALPHA 6E-006
22. DAMP 0.03
23. TYPE STEEL
24. STRENGTH FY 0.25 FU 0.4 RY 1.5 RT 1.2
25. END DEFINE MATERIAL
26. CONSTANTS
27. MATERIAL STEEL ALL
28. UNIT METER KNS
30. TYPE 1 LOAD 90.0 90.0 45.0 DISTANCE 3.0 1.5 WIDTH 3.0
32. SELF Y -1.0
34. TYPE 1 2.25 0. 0. ZI 3.0
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
-----------
SELFWEIGHT  Y   -1.000
ACTUAL WEIGHT OF THE STRUCTURE =     124.391 KNS
-----------
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
8                           -90.0000 GY   0.75
10                           -90.0000 GY   0.75
3                           -45.0000 GY   3.00
2                           -45.0000 GY   3.00
5                           -45.0000 GY   3.00
4                           -45.0000 GY   3.00
3                           -22.5000 GY   4.50
2                           -22.5000 GY   4.50
5                           -22.5000 GY   4.50
4                           -22.5000 GY   4.50
-----------
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
3                           -45.0000 GY   3.00
2                           -45.0000 GY   3.00
5                           -45.0000 GY   3.00
4                           -45.0000 GY   3.00
3                           -45.0000 GY   6.00
2                           -45.0000 GY   6.00
5                           -45.0000 GY   6.00
4                           -45.0000 GY   6.00
3                           -22.5000 GY   7.50
2                           -22.5000 GY   7.50
5                           -22.5000 GY   7.50
4                           -22.5000 GY   7.50
-----------
A SIMPLE BRIDGE DECK                                     -- PAGE NO.    4
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
3                           -45.0000 GY   6.00
2                           -45.0000 GY   6.00
5                           -45.0000 GY   6.00
4                           -45.0000 GY   6.00
19                           -90.0000 GY   0.75
21                           -90.0000 GY   0.75
14                           -22.5000 GY   1.50
13                           -22.5000 GY   1.50
16                           -22.5000 GY   1.50
15                           -22.5000 GY   1.50
-----------
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
19                           -90.0000 GY   0.75
21                           -90.0000 GY   0.75
14                           -45.0000 GY   3.00
13                           -45.0000 GY   3.00
16                           -45.0000 GY   3.00
15                           -45.0000 GY   3.00
14                           -22.5000 GY   4.50
13                           -22.5000 GY   4.50
16                           -22.5000 GY   4.50
15                           -22.5000 GY   4.50
-----------
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
14                           -45.0000 GY   3.00
13                           -45.0000 GY   3.00
16                           -45.0000 GY   3.00
15                           -45.0000 GY   3.00
14                           -45.0000 GY   6.00
13                           -45.0000 GY   6.00
16                           -45.0000 GY   6.00
15                           -45.0000 GY   6.00
14                           -22.5000 GY   7.50
13                           -22.5000 GY   7.50
A SIMPLE BRIDGE DECK                                     -- PAGE NO.    5
16                           -22.5000 GY   7.50
15                           -22.5000 GY   7.50
-----------
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
14                           -45.0000 GY   6.00
13                           -45.0000 GY   6.00
16                           -45.0000 GY   6.00
15                           -45.0000 GY   6.00
30                           -90.0000 GY   0.75
32                           -90.0000 GY   0.75
25                           -22.5000 GY   1.50
24                           -22.5000 GY   1.50
27                           -22.5000 GY   1.50
26                           -22.5000 GY   1.50
-----------
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
30                           -90.0000 GY   0.75
32                           -90.0000 GY   0.75
25                           -45.0000 GY   3.00
24                           -45.0000 GY   3.00
27                           -45.0000 GY   3.00
26                           -45.0000 GY   3.00
25                           -22.5000 GY   4.50
24                           -22.5000 GY   4.50
27                           -22.5000 GY   4.50
26                           -22.5000 GY   4.50
-----------
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
25                           -45.0000 GY   3.00
24                           -45.0000 GY   3.00
27                           -45.0000 GY   3.00
26                           -45.0000 GY   3.00
A SIMPLE BRIDGE DECK                                     -- PAGE NO.    6
25                           -45.0000 GY   6.00
24                           -45.0000 GY   6.00
27                           -45.0000 GY   6.00
26                           -45.0000 GY   6.00
25                           -22.5000 GY   7.50
24                           -22.5000 GY   7.50
27                           -22.5000 GY   7.50
26                           -22.5000 GY   7.50
-----------
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
25                           -45.0000 GY   6.00
24                           -45.0000 GY   6.00
27                           -45.0000 GY   6.00
26                           -45.0000 GY   6.00
41                           -90.0000 GY   0.75
43                           -90.0000 GY   0.75
36                           -22.5000 GY   1.50
35                           -22.5000 GY   1.50
38                           -22.5000 GY   1.50
37                           -22.5000 GY   1.50
-----------
MEMBER LOAD - UNIT KNS  METE
MEMBER     UDL      L1     L2      CON       L     LIN1     LIN2
41                           -90.0000 GY   0.75
43                           -90.0000 GY   0.75
36                           -45.0000 GY   3.00
35                           -45.0000 GY   3.00
38                           -45.0000 GY   3.00
37                           -45.0000 GY   3.00
36                           -22.5000 GY   4.50
35                           -22.5000 GY   4.50
38                           -22.5000 GY   4.50
37                           -22.5000 GY   4.50
************ 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 KNS  METE
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     81.16   0.00    3       0.03   0.00    4
0.00   0.00    1       0.00   0.00    1      0.00     0.00    1
MIN    -31.34   9.00    3    -504.76   9.00    5
0.00   9.00   11       0.00   9.00   11      0.00     9.00   11
41 MAX     73.48   0.00   10       9.18   1.50    5
0.00   0.00    1       0.00   0.00    1      0.00     0.00    1
MIN    -18.36   1.50   11    -147.24   0.75   10
0.00   1.50   11       0.00   1.50   11      0.00     1.50   11
42 MAX      0.30   0.00    1       9.17   0.00    5
0.00   0.00    1       0.00   0.00    1      0.00     0.00    1
MIN     -0.30   1.50    1    -134.84   1.50   10
0.00   1.50   11       0.00   1.50   11      0.00     1.50   11
********** END OF FORCE ENVELOPE FROM INTERNAL STORAGE **********
37. FINISH
*********** END OF THE STAAD.Pro RUN ***********
**** DATE= OCT 19,2021   TIME= 17:53:32 ****
A SIMPLE BRIDGE DECK                                     -- PAGE NO.    8
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