Base Plate Modeling in Staad PDF

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Step by step procedure for plat modelling in STAAD...

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Base Plate Modeling in STAAD.Pro 2007 By

RAM/STAAD Solution Center

24 March 2007

Introduction: Base plates are normally designed using codebase procedures (e.g. AISC-ASD). Engineers often run into situations where there are no codes available to design a particular type of a base plate or there are instances where base plate were simply over designed in the past and the engineer has to check the design of this old base plate based upon new loadings and make modifications as required. In these situations, an engineer may opt to do a finite element analysis on the base plate. STAAD.Pro 2007 is equipped with a lot of mesh generation and loading tools. The purpose of this document is to demonstrate how engineers can analyze base plates using STAAD.Pro 2007.

Figure 2: Plan view of tank base plate

We would like to thank Mr. Indranil Roy Chowdhury, P.Eng. from Hartford Installations, Missisauga, Ontario for allowing us to publish this document. Please note that this document assumes that the user has basic knowledge of STAAD.Pro and Finite Element Analysis. Figure 3: Elevation view of base plate stiffener

Exercise Problem: We would like to create the following base plate geometry in STAAD.Pro. This base plate was used to support a tank leg. The tank leg pipe diameter is 0.9ft and the thickness of the pipe is 0.5 in thick.

1.

Open a new STAAD.Pro file using the space option and the units of ft and kip.

Figure 4: File creation dialog box Figure 1: Isometric sketch of tank base plate

2.

Give an appropriate file name.

3.

Click on the Next button and then click on the Finish button on the following screen.

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The STAAD.Pro interface will appear as shown in Figure 5.

Figure 7: The Base_Plate grid is shown in the Graphics Window.

7.

Draw the outline of the base plate using beam elements. Press the Snap Node/Beam button in the Data Area.

Figure 5: STAAD.Pro user interface

4.

Create a new grid. Click on the Create button in the data area. The Linear input box will appear as shown in Figure 6.

Figure 8: Outline beams created using the grid system.

8.

Now we have to create the pipe section/base plate and the stiffener/base plate interface.

9.

Click on the Create button in the Data Area.

10. Select the Radial grid option and enter the input parameters as shown in Figure 9.

Figure 6: Linear grid box

5.

Input the parameters as shown in Figure 6.

6.

Click on the Ok button. You will notice the Base_Plate Entry in the Data Area.

Figure 9: Circular grid layout for base plate/stiffener and column/stiffener interface.

11. Click the Ok button. 12. Turn on the stiffeners grid and the radial grid will appear in the STAAD.Pro graphics window as illustrated in Figure 10.

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purpose of finite element analysis we should always try to maintain the aspect ratio of the elements. In this case, we performed the translational repeat on the beam elements because we wanted to do a plate infill and create the plate elements. We simply broke the 2.5’ long pipe into 5 sections because we knew that the pipe circumference is broken down into eight 0.5’ lengths. Figure 10:Stiffners grid in the STAAD.Pro Graphics window.

13. Draw the base plate/stiffener column/stiffener interface using stiffeners grid.

and the

Figure 13:Translational Repeat Command.

19. Now we need to create the top portion of the stiffener. You can do this by creating a new stiffener grid at 2.5’ elevation. Figure 11 Base plate/stiffener and column/stiffener interface drawn using the Stiffeners grid.

20. Click on the Geometry->Snap/Grid Node>Beam menu command.

14. Select the beam elements that represent the column/base plate interface.

21. Click on the Create button in the Data Area.

15. Select the Geometry->Translational Repeat menu command.

22. Turn on the stiffeners grid and the radial grid will appear in the graphics window as illustrated in Figure 14.

16. The 3D Repeat dialog box will appear as shown in Figure 12.

Figure 12:Translational Repeat Command.

17. Enter the values in the 3D Repeat dialog box as shown in Figure 12. 18. Click the Ok button. The pipe connected to the base plate will be displayed. For the

Figure 14:Stiffners grid in the STAAD.Pro Graphics window.

23. Click on the Copy button in the Data Area. Type Stiffener_top as the name for the new stiffener grid.

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29. Select the four base nodes of the stiffeners as illustrated in Figure 18.

Figure 15: Copy grid option.

24. You will notice a Stiffener_top entry in the Data Area. Turn on the Stiffener_top grid. 25. Click on the edit button in the Data Area. 26. The Radial grid options dialog box will appear. Enter the parameters as shown in Figure 16.

Figure 18: Four bottom nodes of the stiffener plates selected.

30. Click on Geometry->Translational Repeat menu command.

Figure 19: Translational repeat on the bottom four nodes.

31. Enter the values in the 3D Repeat dialog box as shown in Figure 19. Figure 16:Stiffners grid in the STAAD.Pro Graphics window.

32. Click the Ok button.

27. Click on the Ok button. 28. Draw the top edges of the stiffeners as highlighted in Figure 17.

Figure 20: Vertical edges of plate stiffeners created.

33. Click on Geometry->Add Beam->Add Beam from Point to Point menu command and draw the sloping edges of the stiffeners as shown in Figure 21. Figure 17:Top edges of stiffeners created using the Stiffener_top grid.

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Figure 23: Unwanted elements selected in the graphics window. Figure 21: Sloping edges of plate stiffeners created.

34. We would like to use the Plate Infill command to create the plate elements for the pipe. We will use the Generate Surface Meshing Tool to generate the mesh for the stiffeners. The Parametric Meshing Tool will be used to generate the mesh for the base plate. Select the plan view of the geometry that we have created. 35. Rubberband the beam elements that represent the pipe section. You will end up picking up some unwanted elements also.

38. Select the Select->By Inverse->Inverse Beam Selection menu command. 39. The elements that represent the pipe section will be highlighted. 40. Right click in the graphics window and select the New View option. 41. Select the Display View in Active Window option. 42. Select the isometric view option. 43. Select all the beam elements as shown in Figure 24. You could use the Ctrl+A shortcut keys on your keyboard to select all the beam elements.

Figure 22: Rubberband the elements that represent the pipe section.

36. Click on the View->View Selected Objects Only menu command. 37. Now in the plan view, you will only see the elements that represent the pipe and some stiffener elements. Select all the unwanted elements in the graphics window as shown in Figure 23.

Figure 24: Unwanted elements selected in the graphics window.

44. Select the Geometry->Create Infill Plates menu command. The dialog box shown in Figure 25 will appear.

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51. Enter that inputs in the Insert Node/Nodes dialog box as shown in Figure 25. 52. Get a good isometric view of one of the stiffener plates.

Figure 25: Message Box - 40 plates are created.

53. Rubberband the stiffener plate elements as shown in Figure 26.

46. Click on the Ok button and you will notice that new plate elements are created between the areas bounded by the beam elements. 47. Click on the View->Whole Structure menu command. 48. We will break the sloping part of the stiffeners into five parts. Select the sloping part of the stiffeners in the graphics window as shown in Figure 26.

Figure 26: Stiffener plate selected

54. Click on View->View Selected Objects Only menu command. 55. Select the Geometry->Generate Surface Meshing menu command.

Figure 26: Sloping edges of stiffeners are selected.

49. Click on the Geometry->Insert Node menu command. 50. The Insert Node/Nodes dialog box will appear as shown in Figure 27.

Figure 27: Node Points for Generate Surface Meshing command

56. You will notice that your mouse cursor has changed. Select the nodes on the edge of the stiffener plate in clockwise or counterclockwise fashion as indicated in Figure 27. Select the node that you started off from when you are done.

Figure 25: Insert Node dialog box

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59. Select the Plates cursor and select all the newly created plate elements in the graphic window. 60. Click on Geometry->Circular Repeat menu Command. 61. The 3D Circular dialog box will appear as shown in Figure 31.

Figure 28: Sloping edges of stiffeners are selected.

57. The Define Mesh Region dialog box will appear as shown in Figure 28. Enter 1 for all rows in the Div. column as illustrated in Figure 29. We are telling STAAD.Pro to avoid dividing each of the divided edges into smaller pieces.

Figure 31: Meshing for stiffeners.

62. Enter the inputs in the 3D Circular dialog box as shown in Figure 31. 63. Click the Ok button. You will notice that all the stiffener plates have been created as shown in Figure 32.

Figure 29: Number of edge divisions set to 1.

58. Click on the Ok button. You will note that the meshing for the stiffener has been created as shown in Figure 30.

Figure 32: Meshing for stiffeners.

64. Select the View->Whole Structure menu command. 65. We will need to divide the base plate edges into 12 parts. Select the four base plate edges and select the Geometry->Insert Node menu command.

Figure 30: Meshing for stiffeners.

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74. The Mesh Parameters dialog box will appear as illustrated in Figure 35.

Figure 33: Meshing for stiffeners.

66. The Insert Node/Nodes dialog box will appear as shown in Figure 33. 67. Enter that inputs in the Insert Node/Nodes dialog box as shown in Figure 33. 68. We will draw the base plate using the Parametric Meshing Tool. Click on the Geometry->Parametric Meshing control tab on your left. 69. Click on the Add button in the Data Area. The New Mesh Model dialog box will appear as shown in Figure 34.

Figure 33: Meshing for stiffeners.

75. Set the inputs as shown in Figure 33 and click the Ok button. 76. Click on the No button for the following dialog box. 77. You will see a mesh preview. This preview mode lets the user identify any problems in the FEM model. In Figure 34, we can see that there is a plate connectivity problem at the pipe/base plate interface.

Figure 34: Meshing for stiffeners.

70. Type a mesh name as shown in Figure 34 (i.e. BasePlate). 71. Click on the Ok button. 72. You will notice that the mouse cursor will change.

Figure 34: Meshing for stiffeners.

78. You can resolve this issue by only generating the mesh for regions marked as R1 and R2 and then doing a circular repeat on the mesh.

73. Select the four corner nodes in the clockwise or counter-clockwise fashion and select the starting node once you have selecting four nodes.

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Note that we do not have any connectivity problems in this case. 82. Click on the Setup control tab on the left. 83. Select the Select->Plates Parallel to->XZ menu command. 84. Click on Geometry->Circular Repeat menu command. Enter the inputs as shown in Figure 38.

Figure 35: Mesh generation by regions.

79. We have not documented all these steps in detail in this document. 80. Parametric meshing Type A for B1 (see Figure 36). Figure 38: Circular repeat for Base Plate

85. Click on the Ok button. 86. Select the Select->Plates Parallel to->XZ menu command.

87. Click on View->View Selected Objects Only menu command. 88. Select the Geometry->Generate Surface Meshing menu command. Click on the nodes shown in Red in Figure 39. Figure 36: Mesh generation by regions – Region R1

81. Click on the Merge Mesh button.

Figure 39: Node outline for the Geometry->Generate Surface Meshing menu command

89.

Figure 37: Mesh generation by regions – Region R2

The Define Mesh Region dialog box will appear as shown in Figure 40. Enter 1 for all rows in the Div. column as illustrated in Figure 29. We are telling STAAD.Pro to

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avoid dividing each of the divided edges into smaller pieces.

97. Check if the model is ok from the plate to plate connectivity point of view by clicking on Tools->Check for improperly connected plates menu command. Property Assignment: 98. We will assign 0.5”, 0.4” and 0.6” thickness to the pipe, stiffeners, and base plates respectively.

Figure 40: Number of edge divisions set to 1.

90. Click on the Ok button. 91. Select the View->Whole Structure menu command. 92. Press the Esc key on your keyboard to cancel the Generate Surface Meshing command. 93. Select the beams cursor and press the Ctrl+A key to select all the beams.

99. In a 3D model, it is sometimes difficult to extract a particular section and assign a property to it. For example, it is difficult to select the pipe section out of the 3D model we have and assign the appropriate thickness to it. One could assign plate elements to groups when the geometry is being created. In the case of this example, we know that the number of plates along the circumference = 8 and number of divisions along the height of the pipe= 5. Hence, the number of plates used to create the pipe = 8x5=40 plate elements. Click on Select -> By List -> Plates menu command. 100. The Select Plates dialog box will appear as shown in Figure 42.

94. Press the delete key on your keyboard and press Ok on the following dialog box. 95. Right click in the graphics window and select the 3D Rendering option.

Figure 42: Rendered view of the base plate geometry.

101. The first plate numbering starts from 117. Hence, to select the first fifty plates in the model, we will need to provide the range of 117 to 167 in the Enter List input box. Figure 41: Rendered view of the base plate geometry.

96. Close the rendered mode by simply clicking on the Setup control tab on the left.

102. Click on the Select Listed Entities button in the Select Plates dialog box.

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103. You will notice that the pipe elements will be selected in the Graphics window as illustrated in Figure 43.

111. Press the F2 key on your keyboard. A yellow dialog box will appear as shown in Figure 45.

Figure 45: Unit converter tool

112. Type 0.5 in in the input box and press the Enter key on your keyboard. Figure 43: Pipe plate elements selected in the graphics window.

113. You will notice that STAAD.Pro will automatically convert 0.5 in to 0.041667 ft.

104. Click on the Close button.

114. Click on the Assign button.

105. Click on General control tab on the left.

115. Click on the Close button.

106. The Properties dialog box will appear in the Data Area.

116. Click on the whitespace in the graphics window to get rid of the plate selection.

107. Click on the Thickness button in the Properties dialog box.

117. We will now assign the properties to the base plate.

108. The Plate Thickness dialog box will appear as illustrated in Figure 44.

118. Select the Select->Plates Parallel to->XZ menu command. 119. Click on the Thickness button in the Properties dialog box. 120. The Plate Thickness dialog box will appear as illustrated in Figure 46.

Figure 44: Plate Thickness Dialog Box

109. Select Steel in the Material selection box. 110. We know that the pipe thickness is 0.4” but the input system in the Plate Thickness dialog box is in ft. We can use the unit converter to convert 0.5” to ft. Click in the Node 1 input box.

Figure 46: Plate Thickness Dialog Box

121. Select Steel in the Material selection box.

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122. We know that the base plate thickness is 0.6” but the input system in the Plate Thickness dialog box is in ft. We can use the unit converter to convert 0.6” to ft. Click in the Node 1 input box. 123. Press the F2 key on your keyboard. A yellow dialog box will appear as shown in Figure 47. Figure 48: Plate Thickness Dialog Box

133. Select STEEL in the Material selection box.

Figure 47: Unit converter tool

124. Type 0.6 in in the input box and press the Enter key on your keyboard. 125. You will notice that STAAD.Pro will automatically convert 0.6 in to 0.05 ft.

134. We know that the stiffener thickness is 0.4” but the input system in the Plate Thickness dialog box is in ft. We can use the unit converter to convert 0.4” to ft. Click in the Node 1 input box. 135. Press the F2 key on your keyboard. A yellow dialog box will appear as shown in Figure 49.

126. Click on the Assign button. 127. Click on the Close button. 128. Click on the whitespace in the graphics window to get rid of the plate selection.

Figure 49: Unit converter tool

129. We will now assign the properties to the stiffener plates.

136. Type 0.4 in in the input box and press the Enter key on your keyboard.

130. Select the Select->By Missing Attributes>Missing Properties menu command.

137. You will notice that STAAD.Pro will automatically convert 0.4 in to 0.033333 ft.

131. Click on the Thickness button in the Properties dialog box.

138. Click on the Assign button.

132. The Plate Thickness dialog box will appear as illustrated in Figure 48.

139. Click on the Close button. 140. Click on the whitespace in the graphics window to get rid of the plate selection. 141. Right click in the graphics window and select the 3D Rendering option. You will be able to see the plate thickness in the 3D Rendered mode as illustrated in Figure 50.

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Figure 52: Adding new node

Figure 50: 3D Rendering with plate thickness

142. Close the rendered mode by simply clicking on the Setup control tab on the left. 143. We will need to create a node at the top at (3,2.5,3) to which we will apply a point load. This node will distribute the loading to the column node points.

149. Click on the General->Spec control tab on the left. 150. Click on the Node button. 151. The Node Specification dialog box will appear. Enter the master node number in the Master Node selection box (e.g. 658 in this example as noted in Step# 148 above).

144. Click on the Geometry control tab on the left. 145. You will notice the Nodes Table in the data area as illustrated in Figure 51. Close the Snap Node/Beam dialog box if it is open.

Figure 52: Adding new node

152. Click on the Add button. 153. Select the plan view of the structure. 154. Using the Nodes cursor, select all the nodes at the top of the FEM model as illustrated in Figure 53. Figure 51: Nodes Table

146. Scroll down to the end of the Nodes Table. 147. You will notice a blank cell at the end. 148. Type in coordinates of the new node as shown in Figure 52. This node is the Master Node. Remember this node number. The node number used in this exampl...