Defining and Assigning Properties

In this section, we define Strut/Tie/Node Property Types based on the forces we obtained from the previous step. After that, we assign the Strut/Tie/Node Property Types to the Strut-and-Tie Model. We also need to define the Effective Widths of all STM Elements.

4.1

Referring to Figure 23, we will define two Concrete Strut Types in this step: Prismatic Strut and Bottle-Shaped. Click the button from the Defining toolbar. Alternatively, click the Define menu, point to Strut Types, and click Concrete Struts. CAST will then display the Define Concrete Strut Types dialog box as shown in Figure 24. In this dialog box, do the following:

• Change the Name text box located in the Type List frame to Prismatic Strut.
• Click the Code-Based Equations radio button in the Strut Equation Method frame and select (0) ACI Prismatic Struts from the Code-Based Equations combo box.
• Change the Strength Reduction Factor text box to 0.75.
• Click the Add button located in the Type List frame. The Strut Type name just defined now appears in the Defined Types list box.
• Change the Name text box to Bottle-Shaped.
• Click the Code-Based Equations radio button in the Strut Equation Method frame and select (1) ACI Bottle-Shaped Struts w/ Steel from the Code-Based Equations combo box.
• Change the Strength Reduction Factor text box to 0.75.
• Click the Add button located in the Type List frame.
• Click the OK button to confirm the input and close the window.

Figure 24   The Define Concrete Strut Types Dialog Box
(Click here to view a larger image)

Notes:

• You can skip this step if you decide to use built-in Strut Types. For more information on how to use built-in Strut Types, please see the notes in Step 4.4.

4.2

Click the Define menu, point to Tie Types, and click Non-Prestressed Reinforcement Tie Types (or click the button from the Defining toolbar). CAST will then display the Define Non-Prestressed Reinforcement Tie Types dialog box as shown in Figure 25. In this dialog box:

• Change the Name text box located in the Type List frame to Main Tie.
• Change the Number of Bar Layers text box to 1 by scrolling up/down the scroll button.
• Select the reinforcing bar standard you want to use. Assume that the reinforcing bar for this design is in accordance with ASTM A615/A615M. Therefore, select the ASTM A615/A615M radio button.
• Now define each layer data by entering values in the corresponding text boxes located in the Bar Layer Data (ASTM A615/A615M) frame.
  • Select 1 in the Layer Number text box by scrolling up/down the scroll button, select #25 in the Bar Designation text box by scrolling up/down the scroll button.
  • Change the Number of Bars text box to 6.
  • Enter 0 in the Distance from Reference Line text box.
  • If we have more than one bar layer, change the Layer Number text box to the appropriate layer number and repeat these sub-steps.
• Change the Strength Reduction Factor text box in the Summary frame to 0.75.
• Change the Yield Overstrength Factor text box in the Summary frame to 1.00.
• Assume 50 mm for the tension zone extension, and type in the number in the Tension Zone Extension text box located in the Summary frame.
• Click the Add button located in the Type List frame. The name of properties just defined now appears in the Defined Types list box.
• Click the OK button to confirm the input and close the window.

Figure 25   The Define Non-Prestressed Reinforcement Tie Types Dialog Box
(Click here to view a larger image)

4.3

We will define two node types in this step: CCC and CCT. Select Node Types from the Define menu (or click the button from the Defining toolbar). The Define Node Types dialog box similar to Figure 26 will be displayed. In this dialog box:

• Change the Name text box located in the Type List frame to CCC Node.
• Click the Code-Based Equations radio button in the Node Equation Method frame and select (0) ACI CCC Nodes from the Code-Based Equations combo box.
• Change the Strength Reduction Factor text box to 0.75.
• Click the Add button located in the Type List frame. The node type name just defined now appears in the Defined Types list box.
• Change the Name text box located in the Type List frame to CCT Node.
• Click the Code-Based Equations radio button in the Node Equation Method frame and select (1) ACI CCT Nodes from the Code-Based Equations combo box.
• Change the Strength Reduction Factor text box to 0.75.
• Click the Add button located in the Type List frame.
• Click the OK button to confirm the input and close the window.

Up to this point, we have finished defining the Strut/Tie/Node Property types for our model.

Figure 26   The Define Node Types Dialog Box
(Click here to view a larger image)

Notes:

• You can skip this step if you decide to use built-in Node Types. For more information on how to use built-in Node Types, please see the notes in Step 4.4.

4.4

It is now time to assign Strut/Tie/Node Property Types we have defined in Steps 4.1, 4.2, and 4.3 to the STM Elements and Nodes. We will assign Prismatic Strut type to STM Element IDs E6, E7, E8, E9, E10, E11, E12, E15, and E16 and assign Bottle-Shaped type to STM Element IDs E4 and E5. After that, we will assign Main Tie type to STM Element IDs E1, E2, and E3. We will also assign CCC Node type to STM Node IDs N5 and N6 and assign CCT Node type to STM Node IDs N1, N4, N12, and N13. The last two STM Nodes are nodes carrying the Bearing Plates; they are assigned to Property Types so that their bearing stresses can be checked. See Figure 19 for ID reference.

To assign Strut Property Types to STM Elements:

• Click the button on the button from the Drawing toolbar to be in the Select mode.
• Select STM Element IDs E6, E7, E8, E9, E10, E11, E12, E15, and E16 by either clicking on them or drawing a window around them. The selected elements will become dashed lines.
• Click on the button from the Assigning toolbar (or from the Assign menu, point to Strut or Tie Types, and select User-Defined Struts or Ties). The Assign User-Defined Strut or Tie Types dialog box as shown in Figure 27 will be displayed on the screen.
• Select Concrete Strut from the Property Type combo box.
• Select Prismatic Strut from the Defined Property Type Name combo box.
• Click the OK button.
• Select now STM Element IDs E4 and E5 by either clicking on them or drawing a window around them. The selected elements will become dashed lines.
• Click the button again.
• After the Assign User-Defined Strut or Tie Types dialog box is displayed, select Concrete Strut from the Property Type combo box.
• Select Bottle-Shaped from the Defined Property Type Name combo box.
• Click the OK button to confirm the input and close the window.

Figure 27   The Assign User-Defined Strut or Tie Types Dialog Box

To assign Tie Property Types to STM Elements:

• Click the button on the button from the Drawing toolbar to be in the Select mode.
• Select STM Element IDs E1, E2, and E3 by either clicking on them or drawing a window around them. The selected elements will become dashed lines.
• Click the button again.
• After the Assign User-Defined Strut or Tie Types dialog box appears, select Non-Prestressed Reinforcement Tie from the Property Type combo box.
• Select Main Tie from the Defined Property Type Name combo box.
• Click the OK button to confirm the input and close the window.

To assign the node types to STM Nodes:

• Click the button from the Drawing toolbar to be in the Select mode.
• Select STM Node IDs N5 and N6 by either clicking on them or drawing a window around them.
• Click on the button from the Assigning toolbar (or from the Assign menu, point to Node Types, and click User-Defined Node Types). The Assign User-Defined Node Types dialog box as shown in Figure 28 will be revealed.
• Select CCC Node from the combo box located in the Defined Property Type Name frame.
• Click the OK button.
• Select now STM Node IDs N1 and N4 by either clicking on them or drawing a window around them.
• Click on the button again.
• After the Assign User-Defined Node Types dialog box appears, select CCT Node from the combo box located in the Defined Property Type Name frame.
• Click the OK button to confirm the input and close the window.

Figure 28   The Assign User-Defined Node Types Dialog Box

Notes:

If you skip Steps 4.1 and 4.3, do the following:

• To assign the Strut or Tie Property Types to STM Elements:
  • Click the button on the button from the Drawing toolbar to be in the Select mode.
  • Select STM Element IDs E6, E7, E8, E9, E10, E11, E12, E15, and E16 by either clicking on them or drawing a window around them. The selected elements will become dashed lines.
  • Click the (Assign 'ACI Prismatic Strut' Types) button from the Assigning toolbar.
  • A dialog box showing the default Property Type name will be revealed. Click the OK button to accept the type name.
  • Select now STM Element IDs E4 and E5 by either clicking on them or drawing a window around them. The selected elements will become dashed lines.
  • Click the (Assign 'ACI Bottle-Shaped w/ Steel Strut' Types) button.
  • A similar dialog box showing the default Property Type name will appear. Click the OK button to accept the type name.

• To assign the node types to STM Nodes:

  • Click the button from the Drawing toolbar to be in the Select mode.
  • Select STM Node IDs N5 and N6 by either clicking on them or drawing a window around them.
  • Click the (Assign 'ACI CCC Node' Types) button.
  • A dialog box showing the default Property Type name will appear. Click the OK button to accept the type name.
  • Select now STM Node IDs N1, N4 , N12 , and N13 by either clicking on them or drawing a window around them.
  • Click on the (Assign 'ACI CCT Node' Types) button.
  • Again, a dialog box showing the default Property Type name will appear. Click the OK button to accept the type name.

4.5

We now need to provide the Effective Widths for STM Elements. We will provide a Width of 200 mm for STM Elements IDs E1, E2, and E3, a Width of 300 mm for STM Elements IDs E7, E8, E9, E10, E11, and E12 and 150 mm for STM Elements IDs E4, E5, E6, E15, and E16.

• Click on the button from the Drawing toolbar to be in the Select mode.
• Select STM Element IDs E1, E2, and E3.
• Click on the button from the Assigning toolbar (or click Relative Stiffnesses and Widths from the Assign menu). The Assign Relative Stiffnesses and Widths dialog box as shown in Figure 29 will be displayed.
• Type in 200 in the Provided Effective Width text box.
• Click the OK button.
• Select now STM Element IDs E7, E8, E9, E10, E11, and E12.
• Click on the button again.
• Type in 300 in the Provided Effective Width text box.
• Click the OK button.
• Select STM Element IDs E4, E5, E6, E15, and E16.
• Click on the button again.
• Type in 150 in the Provided Effective Width text box.
• Click the OK button.

Notes:

• Leave all the relative stiffnesses to 1 because the Strut-and-Tie Model used in this design is statically determinate.

Figure 29   The Assign Relative Stiffnesses and Widths Dialog Box

The CAST window now should look like Figure 30. At this stage we have completed the model and are ready to analyze the model.

Figure 30   CAST Window after Step 4.5 
(Click here to view a larger image)

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