EX. US-27 Modeling Soil Springs for a Slab on Grade
This example illustrates the usage of commands necessary to apply the compression only attribute to spring supports for a slab on grade. The spring supports themselves are generated utilizing the built-in support generation facility. The slab is subjected to pressure and overturning loading. A tension/compression only analysis of the structure is performed.
This problem is installed with the program by default to C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\Sample Models\US\US-27 Modeling Soil Springs for a Slab on Grade.STD when you install the program.
The numbers shown in the diagram below are the element numbers.
STAAD SPACE SLAB ON GRADE
* SPRING COMPRESSION EXAMPLE
Every STAAD input file has to begin with the word STAAD. The word SPACE signifies that the structure is a space frame and the geometry is defined through X, Y, and Z axes. An optional title to identify this project is provided in the second line.
SET NL 3
This structure has to be analyzed for 3 primary load cases. Consequently, the modeling of our problem requires us to define 3 sets of data, with each set containing a load case and an associated analysis command. Also, the supports which get switched off in the analysis for any load case have to be restored for the analysis for the subsequent load case. To accommodate these requirements, it is necessary to have 2 commands: SET NL and CHANGE. The SET NL command is used above to indicate the total number of primary load cases that the file contains. The CHANGE command will come in later (after the PERFORM ANALYSIS command).
UNIT FEET KIP
JOINT COORDINATES
1 0.0 0.0 40.0
2 0.0 0.0 36.0
3 0.0 0.0 28.167
4 0.0 0.0 20.333
5 0.0 0.0 12.5
6 0.0 0.0 6.5
7 0.0 0.0 0.0
REPEAT ALL 3 8.5 0.0 0.0
REPEAT 3 8.0 0.0 0.0
REPEAT 5 6.0 0.0 0.0
REPEAT 3 8.0 0.0 0.0
REPEAT 3 8.5 0.0 0.0
For joints 1 through 7, the joint number followed by the X, Y and Z coordinates are specified above. The coordinates of these joints is used as a basis for generating 21 more joints by incrementing the X coordinate of each of these 7 joints by 8.5 feet, 3 times. REPEAT commands are used to generate the remaining joints of the structure. The results of the generation may be visually verified using the STAAD graphical viewing facilities.
ELEMENT INCIDENCES
1 1 8 9 2 TO 6
REPEAT 16 6 7
The incidences of element number 1 is defined and this data is used as a basis for generating the 2nd through the 6th element. The incidence pattern of the first 6 elements is then used to generate the incidences of 96 more elements using the REPEAT command.
UNIT INCH
ELEMENT PROPERTIES
1 TO 102 TH 8.0
The thickness of elements 1 to 102 is specified as 8.0 inches following the command ELEMENT PROPERTIES.
DEFINE MATERIAL START
ISOTROPIC CONCRETE
E 4000.0
POISSON 0.12
DENSITY 8.68e-005
ALPHA 5e-006
DAMP 0.05
G 1346.15
TYPE CONCRETE
STRENGTH FCU 4
END DEFINE MATERIAL
CONSTANTS
MATERIAL CONCRETE ALL
The modulus of elasticity (E) and Poisson’s Ratio are specified following the command CONSTANTS.
SPRING COMPRESSION
1 TO 126 KFY
The above two lines declare the spring supports at nodes 1 to 126 as having the compression-only attribute. The supports themselves are being generated later (see the ELASTIC MAT command which appears later).
UNIT FEET
SUPPORTS
1 TO 126 ELASTIC MAT DIRECTION Y SUBGRADE 12.0
The above command is used to instruct STAAD to generate supports with compression-only springs which are effective in the global Y direction. These springs are located at nodes 1 to 126. The subgrade reaction of the soil is specified as 12 kip/cu.ft. The program will determine the area under the influence of each joint and multiply the influence area by the subgrade reaction to arrive at the spring stiffness for the "FY" degree of freedom at the joint. Units for length are changed to FEET to facilitate the input of subgrade reaction of soil. See TR.27.3 Automatic Spring Support Generator for Foundations .
LOAD 1 'WEIGHT OF MAT & EARTH'
ELEMENT LOAD
1 TO 102 PR GY -1.50
The above data describe a static load case. A pressure load of 1.50 kip/ft acting in the negative global Y direction is applied on all the elements.
PERFORM ANALYSIS PRINT STATICS CHECK
CHANGE
Tension/compression cases must each be followed by PERFORM ANALYSIS and CHANGE commands. The CHANGE command restores the original structure to prepare it for the analysis for the next primary load case.
LOAD 2 'COLUMN LOAD-DL+LL'
JOINT LOADS
1 2 FY -217.
8 9 FY -109.
5 FY -308.7
6 FY -617.4
22 23 FY -410.
29 30 FY -205.
26 FY -542.7
27 FY -1085.4
43 44 50 51 71 72 78 79 FY -307.5
47 54 82 FY -264.2
48 55 76 83 FY -528.3
92 93 FY -205.0
99 100 FY -410.0
103 FY -487.0
104 FY -974.0
113 114 FY -109.0
120 121 FY -217.0
124 FY -273.3
FY -546.6
PERFORM ANALYSIS PRINT STATICS CHECK
CHANGE
Load case 2 consists of several joint loads acting in the negative global Y direction. This is followed by another ANALYSIS command. The CHANGE command restores the original structure once again for the forthcoming load case.
LOAD 3 'COLUMN OVERTURNING LOAD'
ELEMENT LOAD
1 TO 102 PR GY -1.50
JOINT LOADS
1 2 FY -100.
8 9 FY -50.
5 FY -150.7
6 FY -310.4
22 23 FY -205.
29 30 FY -102.
26 FY -271.7
27 FY -542.4
43 44 50 51 71 72 78 79 FY -153.5
47 54 82 FY -132.2
48 55 76 83 FY -264.3
92 93 FY 102.0
99 100 FY 205.0
103 FY 243.0
104 FY 487.0
113 114 FY 54.0
120 121 FY 108.0
124 FY 136.3
125 FY 273.6
PERFORM ANALYSIS PRINT STATICS CHECK
Load case 3 consists of several joint loads acting in the upward direction at one end and downward on the other end to apply an overturning moment that will lift off one end. The CHANGE command is not needed after the last analysis.
LOAD LIST 3
PRINT JOINT DISPLACEMENTS LIST 113 114 120 121
PRINT ELEMENT STRESSES LIST 34 67
PRINT SUPPORT REACTIONS LIST 5 6 12 13
A list of joint displacements, element stresses for elements 34 and 67, and support reactions at a list of joints for load case 3, are obtained with the help of the above commands.
FINISH
The STAAD run is terminated.
Input File
STAAD SPACE SLAB ON GRADE
* SPRING COMPRESSION EXAMPLE
SET NL 3
UNIT FEET KIP
JOINT COORDINATES
1 0.0 0.0 40.0
2 0.0 0.0 36.0
3 0.0 0.0 28.167
4 0.0 0.0 20.333
5 0.0 0.0 12.5
6 0.0 0.0 6.5
7 0.0 0.0 0.0
REPEAT ALL 3 8.5 0.0 0.0
REPEAT 3 8.0 0.0 0.0
REPEAT 5 6.0 0.0 0.0
REPEAT 3 8.0 0.0 0.0
REPEAT 3 8.5 0.0 0.0
ELEMENT INCIDENCES
1 1 8 9 2 TO 6
REPEAT 16 6 7
UNIT INCH
ELEMENT PROPERTIES
1 TO 102 TH 8.0
DEFINE MATERIAL START
ISOTROPIC CONCRETE
E 4000.0
POISSON 0.12
DENSITY 8.68e-005
ALPHA 5e-006
DAMP 0.05
G 1346.15
TYPE CONCRETE
STRENGTH FCU 4
END DEFINE MATERIAL
CONSTANTS
MATERIAL CONCRETE ALL
SPRING COMPRESSION
1 TO 126 KFY
UNIT FEET
SUPPORTS
1 TO 126 ELASTIC MAT DIRECTION Y SUBGRADE 12.0
LOAD 1 'WEIGHT OF MAT & EARTH'
ELEMENT LOAD
1 TO 102 PR GY -1.50
PERFORM ANALYSIS PRINT STATICS CHECK
CHANGE
LOAD 2 'COLUMN LOAD-DL+LL'
JOINT LOADS
1 2 FY -217.
8 9 FY -109.
5 FY -308.7
6 FY -617.4
22 23 FY -410.
29 30 FY -205.
26 FY -542.7
27 FY -1085.4
43 44 50 51 71 72 78 79 FY -307.5
47 54 82 FY -264.2
48 55 76 83 FY -528.3
92 93 FY -205.0
99 100 FY -410.0
103 FY -487.0
104 FY -974.0
113 114 FY -109.0
120 121 FY -217.0
124 FY -273.3
125 FY -546.6
PERFORM ANALYSIS PRINT STATICS CHECK
CHANGE
LOAD 3 'COLUMN OVERTURNING LOAD'
ELEMENT LOAD
1 TO 102 PR GY -1.50
JOINT LOADS
1 2 FY -100.
8 9 FY -50.
5 FY -150.7
6 FY -310.4
22 23 FY -205.
29 30 FY -102.
26 FY -271.7
27 FY -542.4
43 44 50 51 71 72 78 79 FY -153.5
47 54 82 FY -132.2
48 55 76 83 FY -264.3
92 93 FY 102.0
99 100 FY 205.0
103 FY 243.0
104 FY 487.0
113 114 FY 54.0
120 121 FY 108.0
124 FY 136.3
125 FY 273.6
PERFORM ANALYSIS PRINT STATICS CHECK
LOAD LIST 3
PRINT JOINT DISPLACEMENTS LIST 113 114 120 121
PRINT ELEMENT STRESSES LIST 34 67
PRINT SUPPORT REACTIONS LIST 5 6 12 13
FINISH
STAAD Output File
PAGE NO. 1 **************************************************** * * * STAAD.Pro CONNECT Edition * * Version 22.12.00.*** * * Proprietary Program of * * Bentley Systems, Inc. * * Date= OCT 27, 2022 * * Time= 15: 9:53 * * * * Licensed to: Bentley Systems Inc * **************************************************** 1. STAAD SPACE SLAB ON GRADE INPUT FILE: US-27 Modeling Soil Springs for a Slab on Grade.STD 2. * SPRING COMPRESSION EXAMPLE 3. SET NL 3 4. UNIT FEET KIP 5. JOINT COORDINATES 6. 1 0.0 0.0 40.0 7. 2 0.0 0.0 36.0 8. 3 0.0 0.0 28.167 9. 4 0.0 0.0 20.333 10. 5 0.0 0.0 12.5 11. 6 0.0 0.0 6.5 12. 7 0.0 0.0 0.0 13. REPEAT ALL 3 8.5 0.0 0.0 14. REPEAT 3 8.0 0.0 0.0 15. REPEAT 5 6.0 0.0 0.0 16. REPEAT 3 8.0 0.0 0.0 17. REPEAT 3 8.5 0.0 0.0 18. ELEMENT INCIDENCES 19. 1 1 8 9 2 TO 6 20. REPEAT 16 6 7 21. UNIT INCH 22. ELEMENT PROPERTIES 23. 1 TO 102 TH 8.0 24. DEFINE MATERIAL START 25. ISOTROPIC CONCRETE 26. E 4000.0 27. POISSON 0.12 28. DENSITY 8.68E-005 29. ALPHA 5E-006 30. DAMP 0.05 31. G 1346.15 32. TYPE CONCRETE 33. STRENGTH FCU 4 34. END DEFINE MATERIAL 35. CONSTANTS 36. MATERIAL CONCRETE ALL 37. SPRING COMPRESSION 38. 1 TO 126 KFY SLAB ON GRADE -- PAGE NO. 2 * SPRING COMPRESSION EXAMPLE 39. UNIT FEET 40. SUPPORTS 41. 1 TO 126 ELASTIC MAT DIRECTION Y SUBGRADE 12.0 42. LOAD 1 'WEIGHT OF MAT & EARTH' 43. ELEMENT LOAD 44. 1 TO 102 PR GY -1.50 45. PERFORM ANALYSIS PRINT STATICS CHECK P R O B L E M S T A T I S T I C S ----------------------------------- NUMBER OF JOINTS 126 NUMBER OF MEMBERS 0 NUMBER OF PLATES 102 NUMBER OF SOLIDS 0 NUMBER OF SURFACES 0 NUMBER OF SUPPORTS 126 Using 64-bit analysis engine. SOLVER USED IS THE IN-CORE ADVANCED MATH SOLVER TOTAL PRIMARY LOAD CASES = 1, TOTAL DEGREES OF FREEDOM = 378 TOTAL LOAD COMBINATION CASES = 0 SO FAR. SLAB ON GRADE -- PAGE NO. 3 * SPRING COMPRESSION EXAMPLE **NOTE-Tension/Compression converged after 1 iterations, Case= 1 STATIC LOAD/REACTION/EQUILIBRIUM SUMMARY FOR CASE NO. 1 'WEIGHT OF MAT & EARTH' CENTER OF FORCE BASED ON Y FORCES ONLY (FEET). (FORCES IN NON-GLOBAL DIRECTIONS WILL INVALIDATE RESULTS) X = 0.645000019E+02 Y = 0.000000000E+00 Z = 0.200000006E+02 TOTAL APPLIED LOAD 1 ***TOTAL APPLIED LOAD ( KIP FEET ) SUMMARY (LOADING 1 ) SUMMATION FORCE-X = 0.00 SUMMATION FORCE-Y = -7740.00 SUMMATION FORCE-Z = 0.00 SUMMATION OF MOMENTS AROUND THE ORIGIN- MX= 154800.01 MY= 0.00 MZ= -499230.03 TOTAL REACTION LOAD 1 ***TOTAL REACTION LOAD( KIP FEET ) SUMMARY (LOADING 1 ) SUMMATION FORCE-X = 0.00 SUMMATION FORCE-Y = 7740.00 SUMMATION FORCE-Z = 0.00 SUMMATION OF MOMENTS AROUND THE ORIGIN- MX= -154800.01 MY= 0.00 MZ= 499230.03 MAXIMUM DISPLACEMENTS ( INCH /RADIANS) (LOADING 1) MAXIMUMS AT NODE X = 0.00000E+00 0 Y = -1.50000E+00 1 Z = 0.00000E+00 0 RX= 9.79653E-10 121 RY= 0.00000E+00 0 RZ= 4.32018E-10 45 ************ END OF DATA FROM INTERNAL STORAGE ************ 46. CHANGE 47. LOAD 2 'COLUMN LOAD-DL+LL' 48. JOINT LOADS 49. 1 2 FY -217. 50. 8 9 FY -109. 51. 5 FY -308.7 52. 6 FY -617.4 53. 22 23 FY -410. 54. 29 30 FY -205. SLAB ON GRADE -- PAGE NO. 4 * SPRING COMPRESSION EXAMPLE 55. 26 FY -542.7 56. 27 FY -1085.4 57. 43 44 50 51 71 72 78 79 FY -307.5 58. 47 54 82 FY -264.2 59. 48 55 76 83 FY -528.3 60. 92 93 FY -205.0 61. 99 100 FY -410.0 62. 103 FY -487.0 63. 104 FY -974.0 64. 113 114 FY -109.0 65. 120 121 FY -217.0 66. 124 FY -273.3 67. 125 FY -546.6 68. PERFORM ANALYSIS PRINT STATICS CHECK SLAB ON GRADE -- PAGE NO. 5 * SPRING COMPRESSION EXAMPLE **NOTE-Tension/Compression converged after 1 iterations, Case= 2 STATIC LOAD/REACTION/EQUILIBRIUM SUMMARY FOR CASE NO. 2 'COLUMN LOAD-DL+LL' CENTER OF FORCE BASED ON Y FORCES ONLY (FEET). (FORCES IN NON-GLOBAL DIRECTIONS WILL INVALIDATE RESULTS) X = 0.633725605E+02 Y = 0.000000000E+00 Z = 0.215722031E+02 TOTAL APPLIED LOAD 2 ***TOTAL APPLIED LOAD ( KIP FEET ) SUMMARY (LOADING 2 ) SUMMATION FORCE-X = 0.00 SUMMATION FORCE-Y = -13964.90 SUMMATION FORCE-Z = 0.00 SUMMATION OF MOMENTS AROUND THE ORIGIN- MX= 301253.66 MY= 0.00 MZ= -884991.47 TOTAL REACTION LOAD 2 ***TOTAL REACTION LOAD( KIP FEET ) SUMMARY (LOADING 2 ) SUMMATION FORCE-X = 0.00 SUMMATION FORCE-Y = 13964.90 SUMMATION FORCE-Z = 0.00 SUMMATION OF MOMENTS AROUND THE ORIGIN- MX= -301253.66 MY= 0.00 MZ= 884991.47 MAXIMUM DISPLACEMENTS ( INCH /RADIANS) (LOADING 2) MAXIMUMS AT NODE X = 0.00000E+00 0 Y = -1.12956E+01 120 Z = 0.00000E+00 0 RX= 8.11932E-02 99 RY= 0.00000E+00 0 RZ= 1.00569E-01 6 ************ END OF DATA FROM INTERNAL STORAGE ************ 69. CHANGE 70. LOAD 3 'COLUMN OVERTURNING LOAD' 71. ELEMENT LOAD 72. 1 TO 102 PR GY -1.50 73. JOINT LOADS 74. 1 2 FY -100. 75. 8 9 FY -50. 76. 5 FY -150.7 77. 6 FY -310.4 SLAB ON GRADE -- PAGE NO. 6 * SPRING COMPRESSION EXAMPLE 78. 22 23 FY -205. 79. 29 30 FY -102. 80. 26 FY -271.7 81. 27 FY -542.4 82. 43 44 50 51 71 72 78 79 FY -153.5 83. 47 54 82 FY -132.2 84. 48 55 76 83 FY -264.3 85. 92 93 FY 102.0 86. 99 100 FY 205.0 87. 103 FY 243.0 88. 104 FY 487.0 89. 113 114 FY 54.0 90. 120 121 FY 108.0 91. 124 FY 136.3 92. 125 FY 273.6 93. PERFORM ANALYSIS PRINT STATICS CHECK SLAB ON GRADE -- PAGE NO. 7 * SPRING COMPRESSION EXAMPLE *** LOAD CASE 3 -- START ITERATION NO. 2 *** LOAD CASE 3 -- START ITERATION NO. 3 *** LOAD CASE 3 -- START ITERATION NO. 4 *** LOAD CASE 3 -- START ITERATION NO. 5 **NOTE-Tension/Compression converged after 5 iterations, Case= 3 STATIC LOAD/REACTION/EQUILIBRIUM SUMMARY FOR CASE NO. 3 'COLUMN OVERTURNING LOAD' CENTER OF FORCE BASED ON Y FORCES ONLY (FEET). (FORCES IN NON-GLOBAL DIRECTIONS WILL INVALIDATE RESULTS) X = 0.454460478E+02 Y = 0.000000000E+00 Z = 0.202712741E+02 TOTAL APPLIED LOAD 3 ***TOTAL APPLIED LOAD ( KIP FEET ) SUMMARY (LOADING 3 ) SUMMATION FORCE-X = 0.00 SUMMATION FORCE-Y = -10533.10 SUMMATION FORCE-Z = 0.00 SUMMATION OF MOMENTS AROUND THE ORIGIN- MX= 213519.36 MY= 0.00 MZ= -478687.78 TOTAL REACTION LOAD 3 ***TOTAL REACTION LOAD( KIP FEET ) SUMMARY (LOADING 3 ) SUMMATION FORCE-X = 0.00 SUMMATION FORCE-Y = 10533.10 SUMMATION FORCE-Z = 0.00 SUMMATION OF MOMENTS AROUND THE ORIGIN- MX= -213519.36 MY= 0.00 MZ= 478687.78 MAXIMUM DISPLACEMENTS ( INCH /RADIANS) (LOADING 3) MAXIMUMS AT NODE X = 0.00000E+00 0 Y = 3.06386E+01 120 Z = 0.00000E+00 0 RX= -1.35247E-01 120 RY= 0.00000E+00 0 RZ= 1.12342E-01 125 ************ END OF DATA FROM INTERNAL STORAGE ************ 94. LOAD LIST 3 95. PRINT JOINT DISPLACEMENTS LIST 113 114 120 121 JOINT DISPLACE LIST 113 SLAB ON GRADE -- PAGE NO. 8 * SPRING COMPRESSION EXAMPLE JOINT DISPLACEMENT (INCH RADIANS) STRUCTURE TYPE = SPACE ------------------ JOINT LOAD X-TRANS Y-TRANS Z-TRANS X-ROTAN Y-ROTAN Z-ROTAN 113 3 0.00000 20.81368 0.00000 -0.10277 0.00000 0.07382 114 3 0.00000 15.82565 0.00000 -0.10134 0.00000 0.06799 120 3 0.00000 30.63862 0.00000 -0.13525 0.00000 0.10711 121 3 0.00000 24.13106 0.00000 -0.12907 0.00000 0.09243 ************** END OF LATEST ANALYSIS RESULT ************** 96. PRINT ELEMENT STRESSES LIST 34 67 ELEMENT STRESSES LIST 34 SLAB ON GRADE -- PAGE NO. 9 * SPRING COMPRESSION EXAMPLE ELEMENT STRESSES FORCE,LENGTH UNITS= KIP FEET ---------------- STRESS = FORCE/UNIT WIDTH/THICK, MOMENT = FORCE-LENGTH/UNIT WIDTH ELEMENT LOAD SQX SQY MX MY MXY VONT VONB SX SY SXY TRESCAT TRESCAB 34 3 -4.66 -6.79 2.34 7.95 5.74 164.71 164.71 0.00 0.00 0.00 172.44 172.44 TOP : SMAX= 155.71 SMIN= -16.73 TMAX= 86.22 ANGLE= 58.0 BOTT: SMAX= 16.73 SMIN= -155.71 TMAX= 86.22 ANGLE=-32.0 67 3 32.82 6.55 -63.47 5.72 36.48 1238.45 1238.45 0.00 0.00 0.00 1357.37 1357.37 TOP : SMAX= 288.91 SMIN= -1068.46 TMAX= 678.69 ANGLE= 66.7 BOTT: SMAX= 1068.46 SMIN= -288.91 TMAX= 678.69 ANGLE=-23.3 **** MAXIMUM STRESSES AMONG SELECTED PLATES AND CASES **** MAXIMUM MINIMUM MAXIMUM MAXIMUM MAXIMUM PRINCIPAL PRINCIPAL SHEAR VONMISES TRESCA STRESS STRESS STRESS STRESS STRESS 1.068459E+03 -1.068459E+03 6.786865E+02 1.238454E+03 1.357373E+03 PLATE NO. 67 67 67 67 67 CASE NO. 3 3 3 3 3 ********************END OF ELEMENT FORCES******************** 97. PRINT SUPPORT REACTIONS LIST 5 6 12 13 SUPPORT REACTION LIST 5 SLAB ON GRADE -- PAGE NO. 10 * SPRING COMPRESSION EXAMPLE SUPPORT REACTIONS -UNIT KIP FEET STRUCTURE TYPE = SPACE ----------------- JOINT LOAD FORCE-X FORCE-Y FORCE-Z MOM-X MOM-Y MOM Z 5 3 0.00 149.37 0.00 0.00 0.00 0.00 6 3 0.00 170.57 0.00 0.00 0.00 0.00 12 3 0.00 148.42 0.00 0.00 0.00 0.00 13 3 0.00 152.40 0.00 0.00 0.00 0.00 ************** END OF LATEST ANALYSIS RESULT ************** 98. FINISH SLAB ON GRADE -- PAGE NO. 11 * SPRING COMPRESSION EXAMPLE *********** END OF THE STAAD.Pro RUN *********** **** DATE= OCT 27,2022 TIME= 15: 9:54 **** ************************************************************ * For technical assistance on STAAD.Pro, please visit * * http://www.bentley.com/en/support/ * * * * Details about additional assistance from * * Bentley and Partners can be found at program menu * * Help->Technical Support * * * * Copyright (c) Bentley Systems, Inc. * * http://www.bentley.com * ************************************************************