Overview
In this document, the task of designing a double corbel is completed to illustrate how the CAST Design Tool (Version 0.9.10)
can be used for the design of D- (Discontinuity) Regions. Following a brief introduction and description of the CAST graphical
user interface, a step-by-step solution is presented. In order to describe many of the important features of this program,
complete details are provided with associated images from CAST. The completion of this exercise and thus familiarization
with CAST is estimated to take 60 minutes.
Introduction
Figure 1 describes the geometry and loadings for the double corbel structure being considered. The thickness of the corbel is
600 mm. The concrete strength is 35 MPa, and the yield strength of reinforcement is taken as 420 MPa. The corbel supports
an ultimate vertical force of 1000 kN and an ultimate horizontal force of 100 kN at each end and two ultimate point loads of
3000 kN in the supporting column region. Bearing plates of 150 mm length x 600 mm width x 25 mm thick are provided at
each end of the corbel. Figure 2 shows the selected strut-and-tie model for this structure. The design will be completed to
meet ACI 318-02 Appendix A requirements.

Figure 1 The Geometry and the Loadings of the Corbel under Consideration

Figure 2 Strut-and-Tie Model Employed in this Corbel Design
CAST Window
Creation/modification of the structure’s geometry and strut-and-tie model, execution of the truss analysis, and stress checks
using CAST Design Tool are all done through the CAST Graphical User Interface (GUI). The CAST GUI that appears on your
screen will look similar to Figure 3. This interface consists of several components as labeled in Figure 3. Please familiarize
yourself with the names of these interface components as they will be used throughout this handout.
Figure 3 A Typical CAST Window
(Click here to view a larger image)
Notes:
• The screen shown in this handout may look slightly different from your computer’s screen due to different toolbar
positions and different settings of screen resolution and fonts.
• In addition, several terminologies used in CAST Design Tool are explained below:
 D-Region Boundary:
o A closed, non-intersecting polygon that defines the geometry of the structure.
o There are two types of D-Region Boundaries: Outer Boundary (Perimeter) and Inner Boundary (for

openings).
o You are allowed to create only one Outer Boundary, but you can create as many Inner Boundaries as
you want.
o Because there is only one Outer Boundary that should exist in your model and the region inside the
Outer Boundary represents the concrete continuum, you are not allowed to copy, cut, or remove it
from your model once you create it. However, you are surely allowed to change the positions of the
Boundary Corners. You are also allowed to add and remove Boundary Corners as you wish.
 D-Region Boundary Corner:
o Intersection of two Boundary Edges.
 D-Region Boundary Edge:
o Line connecting two Boundary Corners.
o Place for STM Nodes that possess Bearing Plates, Point Loads, or Point Supports.
 Strut-and-Tie Model:
o Internal truss in the D-Region.
o Consists of STM Elements interconnected at STM Nodes.
 STM Element:
o Component of Strut-and-Tie Model.
o STM Elements can be in the form of Struts (compressive STM Elements) or Ties (tensile STM
Elements).
o STM Elements have Effective Widths, representing the extent of idealized compressive stress fields
(for Struts) or tensile stress fields (for Ties).
 STM Node:
o Component of Strut-and-Tie Model.
o Place where one or more STM Elements meet, also called a nodal zone.
o There is only one STM Element allowed to frame into an STM Node having Bearing Plates, Point
Loads, or Point Supports.
 Stabilizer:
o STM Element whose member force is zero.
o Stabilizers are not included in the nodal zone construction.
o Stabilizers are required to avoid ill-conditioned structure stiffness matrix in truss analysis.

o You must always create a stable Strut-and-Tie Model; Stabilizers are identified by CAST during truss
analysis.
o See Q & A #4 for more detail about Stabilizers.
Getting Started
In this section, we start the program, set the units, create a new model file, define project description, define general
properties, setup Guidelines, and save the model in a file.
1.1 Click Start menu of the Windows operating system, point
to Programs, point to CAST, and then click CAST. This
starts the CAST program. A CAST window followed by the
CAST splash screen then appears. After this, if the Tip of the
Day dialog box like the one shown in Figure 4 is displayed,
close it by clicking the OK button.
Figure 4 The Tip of the Day Dialog Box
1.2 Select the active unit you want to work with from the Active
Unit of Measure combo box (seeFigure 5) located in
the Standard toolbar. Since our design problem is given in SI
unit, select SI Unit.
Figure 5 The Active Unit of Measure Combo Box
Note:You can change the units at any time; CAST will handle
all the conversion automatically
1.3
Click the button (or select New from the File menu).
CAST responds by displaying the Define Project
Description dialog box shown in Figure 6. In this dialog box:
• Change the Project Name text box to Double
Corbel.
• Provide a name in the Designer text box. In our
case, assume that the designers are Sabrina and
Julius, so type in Sabrina & Julius.
• Change the Date text box to current date, let

say 4/2/2002.
• Enter any important notes in the Notes text box. In
our case, type in Example for CAST Tutorial.
• Click the OK button to confirm the input and close
the window.
Figure 6 The Define Project Description Dialog Box
Note: The Define Project Description dialog box can be
later displayed for editing by clickingProject
Description from the Define menu (or by pressing Ctrl+D
key combination). Alternatively, it can be displayed by clicking
the button from the Defining toolbar.
1.4 CAST will then display the Define General Properties dialog
box shown in Figure 7. This dialog box allows us to define
the thickness of the structure under consideration, the
concrete cylinder strength, and the steel yield strength.
• Type in 600 in the D-Region Thickness text box.
• Type in 35 in the Concrete Cylinder Strength,
f'c text box.
• Leave the Concrete Tensile Strength, f'ct text box
blank.
• Type in 420 in the Non-Prestressed
Reinforcement Yield Strength, fy text box.
• Click the OK button to confirm the input and close
the window.
Figure 7 The Define General Properties Dialog
Box
Note:
• The Define General Properties dialog box can be
later displayed for editing by clickingGeneral
Properties from the Define menu (or by pressing

Ctrl+T key combination). Alternatively, it can be
displayed by clicking the button from
the Defining toolbar.
1.5 Now, we will create Guidelines to help determine the
geometry of the model. To do this, clickGuidelines from
the Construct menu. CAST will display the Construct
Guidelines dialog box shown in Figure 8. In this dialog box:
• Check the Glue Boundary Corners or STM Nodes
to Guidelines checkbox to turn on this option. If this
option is on, it lets you edit D-Region Boundary
Corners and/or STM Node locations by simply
editing the Guidelines.
• Check the Snap Boundary Corners or STM Nodes
to Guidelines checkbox to turn on this option. If this
option is on, a D-Region Boundary Corner or an STM
Node drawn or moved near a vertical and horizontal
Guideline will snap to it. This option guarantees that
new generated Boundary Corners or STM Nodes will
be precisely placed on Vertical and Horizontal
Guidelines as well as at the intersection of Vertical
and Horizontal Guidelines. This option can also be
activated from the Snapping toolbar: when on
and when off.
• Select the type of the Guidelines we want to
add/move/delete. Let’s begin with the Vertical
Guidelines by clicking on the text box of
the Distance from Y-Axis frame located in
theVertical Guidelines frame.
• Add Vertical Guidelines. In our case, we need twelve
Vertical Guidelines, i.e., at location X=-1000, X=-910,

X=-900, X=-500, X=-250, X=0, X=125, X=250,
X=500, X=900, X=910, X=1000. Enter each number
in the text box of the Distance from Y-Axis frame
located in the Vertical Guidelines frame followed by
clicking the Add button.
• After completing Vertical Guideline locations, do the
same for Horizontal Guidelines. In our case, we need
six Horizontal Guidelines, i.e., at location Y=-600,
Y=0, Y=400, Y=900, Y=1000, Y=1500. Enter each
number in the text box of the Distance from X-
Axis frame located in the Horizontal
Guidelines frame followed by clicking
the Add button.
• Press the OK button to confirm the input and close
the window.
Figure 8 The Construct Guidelines Dialog Box.
Notes:
• Guidelines are lines that we create to help us
determine the geometry of the model. The Boundary
Corners and STM Nodes of our structural model are
usually located at intersections of Vertical and
Horizontal Guidelines.
• We can later display the Construct
Guidelines dialog box for editing by
clickingGuidelines from the Construct menu (or by
pressing Shift+F3 key combination or by clicking
the button from the Standard toolbar).
• When a Guideline is visible on a display window,
the Construct Guidelines dialog box can also be
displayed by double clicking on the Guideline.

• If you want to change a Guideline location (a Vertical
Guideline for example):
 Select the Guideline location you want to
change from the list box in the Defined
Locations frame.
 The Guideline location value will appear in
the text box of the Distance from Y-
Axisframe. Edit the value in this text box.
 Click the Modify button in the Vertical
Guidelines frame.
 Click the OK button to confirm the change
and close the window.
• To delete a defined Guideline (a Vertical Guideline
for example):
 Select the Guideline location you want to
delete from the list box in the Defined
Locations frame.
 Click the Delete button in the Vertical
Guidelines frame.
 Click the OK button to confirm the deletion
and close the window.
The screen will then refresh and will look similar to Figure 9.
Figure 9 CAST Window after Step 1.5
(Click here to view a larger image)
Notes:
• We can have multiple display windows to view our
structural model at the same time. To add a new
display window, click the Window menu, point
to New Window, and click on one of the Load
Condition names listed. To arrange the positions of

the display windows, select one of the four options
available (Tile Horizontally/Tile
Vertically/Cascade/Arrange Icons) from
the Window menu.
• We can hide/display the Guidelines of the active
display window by clicking Show Guidelines from
the View menu (or by pressing F3 key). Similarly, we
can hide/display the axes shown in an active display
window by choosing Show Axes from
the View menu (or by pressing F4 key).
• In addition to Guidelines, CAST also provides Grid
Points to help us determine the geometry of our
model. To setup Grid Points, select Grid Points from
the Construct menu (or press Shift+F2 key
combination). The Construct Grid Points dialog box
similar to Figure 10 will then appear on the screen. In
this dialog box, we can:
 Set the horizontal or vertical interval of Grid
Points by entering the horizontal or vertical
text box in the Grid Point Interval frame.
 If you want to store the specified horizontal
or vertical Grid Point interval in file to be
used for the next opening of CAST, click
the Save As Defaults button. The Grid Point
interval will be stored in CAST.INI.
 Check the Snap Boundary Corners or STM
Nodes to Grid Points checkbox to turn on
this option. If this option is turned on, a D-
Region Boundary Corner and/or STM Node
drawn or moved near a Grid Point will snap

to it. This option guarantees that new
generated D-Region Boundary Corners
and/or STM Nodes will be precisely placed
at the grid points. This option can also be
activated from the Snappingtoolbar:
when on and when off.
Figure 10 The Construct Grid Points Dialog Box
1.6 Although you have not finished creating the model, you
should save your work at this early stage. To save the model
for the first time, do the following:
• Select Save As or Save from the File menu (or use
Ctrl+S key combination, or click the button from
the Standard toolbar). CAST responds by displaying
the Save As dialog box shown in Figure 11.
• Change the directory to your working directory. In
this case, assume that the working directory
is c:\CAST\Files.
• Provide a file name in the File name text box. In this
case, assume that the file name isDCorbel. CAST
will then automatically build an extension of .CST to
the file name.
• Click the Save button.
It is also a good idea to save your work from time to time
because you will have to do the unsaved work again if your
PC system collapses before you save your work. To save
your work, select Savefrom the File menu (or use Ctrl+S key
combination, or click the button from
the Standardtoolbar).
Figure 11 The Save As Dialog Box
Constructing the Model

In this section, we construct the D-Region Boundaries and the Strut-and-Tie Model. After that, we define and assign Bearing
Plates (if any), Point Loads, and Point Supports.
2.1 We will use the Guidelines constructed in Step 1.5 to help us
create our D-Region Boundaries. If you do not see the
Guidelines on the screen, click Show Guidelines from
the View menu. This creates a rectangle surrounding the
icon next to it and works as a toggle to turn on/off the
Guidelines. Make sure that the Snap Boundary Corners or
STM Nodes to Guidelines button located in
the Snapping toolbar is on by clicking it: when on
and when off. Click then the button (or click
the Construct menu and then click Outer Boundary) to
switch to the Draw mode. Next, create the D-Region
Boundary by placing the Boundary Corners at the Guideline
intersections as follows:
• Click on the intersection of Guideline X=-1000 and
Guideline Y=1000
• Click on the intersection of Guideline X=-500 and
Guideline Y=1000.
• Click on the intersection of Guideline X=-500 and
Guideline Y=1500.
• Click on the intersection of Guideline X=500 and
Guideline Y=1500.
• Click on the intersection of Guideline X=500 and
Guideline Y=1000.
• Click on the intersection of Guideline X=1000 and
Guideline Y=1000.
• Click on the intersection of Guideline X=1000 and
Guideline Y=400.
• Click on the intersection of Guideline X=500 and

Guideline Y=0.
• Click on the intersection of Guideline X=500 and
Guideline Y=-600.
• Click on the intersection of Guideline X=-500 and
Guideline Y=-600.
• Click on the intersection of Guideline X=-500 and
Guideline Y=0.
• Click on the intersection of Guideline X=-1000 and
Guideline Y=400.
• Click on the intersection of Guideline X=-1000 and
Guideline Y=1000 to close the D-Region Boundary.
This last step can also be accomplished by simply
clicking the right button of your mouse.
Up to this point, we have finished drawing the geometry of
the structure as shown in Figure 12.
Figure 12 CAST Window after Step 2.1
(Click here to view a larger image)
Notes:
• You can create openings within the D-Region, if any,
in the same manner as you create the Outer
Boundary, except that you must click the
button (or click again the Constructmenu and then
click Inner Boundaries).
• You must first create the Outer Boundary before you
can create Inner Boundaries and Strut-and-Tie
Model.
• You are allowed to create only one Outer Boundary,
but you can create as many Inner Boundaries (to
represent openings) as you want.
• If you hold the Shift key while drawing, it turns on the

orthogonal mode. In this mode, all lines you make
will be parallel to either X or Y axis.
• If you make a mistake, for example, you draw an
element at a wrong place, you can undo your work
by clicking the button from the Standard toolbar
or clicking Undo from theEdit menu (or by pressing
Ctrl+Z key combination).
• You can also move/add/remove an Outer or Inner
Boundary Corner by clicking the button to
switch to Modify mode (or by selecting Edit
Boundaries from the Edit menu), and then:
 To move the whole D-Region Boundary,
simply drag it to the desired position. If
the (Snap Boundary Corners or STM
Nodes to Grid Points) or the (Snap
Boundary Corners or STM Nodes to
Guidelines) option is turned on, the centroid
of the D-Region Boundary enclosed area will
be snapped to any Grid Points or Guidelines
while dragging.
 Similarly, to move a corner position, drag the
corner to the desired position. If the
(Snap Boundary Corners or STM Nodes
to Grid Points) or the (Snap Boundary
Corners or STM Nodes to Guidelines)
option is turned on, the corner will be
snapped to any Grid Points or Guidelines
while dragging.
 To add or remove a corner:
o Right click on a corner or an edge.

The pop-up menu similar to Figure
13 will be displayed.
o Click Add Corner to add a corner.
Click Remove Corner to remove a
corner.
• Pressing the Esc key will terminate the Draw mode
and take you back to the Select mode.
• You can adjust object sizes by using the
object size adjusters located at the status bar. The
most left control can be used to adjust the font sizes
in the display window. The middle control is used to
adjust the line thickness of D-Region Boundary, STM
Element, and Bearing Plate objects and to adjust the
diameter of STM Node objects. The most right
control is used to adjust the length of Point Load and
Point Support objects.

Figure 13 The Pop-up Menu for Adding or Removing D-
Region Boundary Corners
2.2 Let’s now draw the geometry of the Strut-and-Tie Model.
Again, we will again use the Guidelines to help us create the
geometry. Click the button (or select STM
Elements from the Constructmenu) to switch to the Draw
mode. Make sure that the Snap and Glue STM Nodes to
Other STM Nodes option is on by clicking it: when on
and when off. Also, make sure that theSnap STM Nodes
to Boundary Edges option is on by clicking it: when on
and when off. The (Snap STM Elements
Perpendicular to Boundary Edges) option allows the STM
Elements drawn to be perpendicular to Boundary Edges.

We also need to show STM Element and Node IDs for our
later reference. This is done by clicking the button from
the Standard toolbar or by selecting Set Object View
Options menu from theView menu and then clicking
the OK button. This will show the Set Object View
Options dialog box as shown in Figure 14. In this dialog box,
check Node IDs and Element IDs checkboxes in the Strut-
and-Tie Model frame, and then click the OK button.
Figure 14 The Set Object View Options Dialog Box
(Click here to view a larger image)
Now, do the following:
• Click on the intersection of Guideline X=-910 and
Guideline Y=900, and then click on the intersection
of Guideline X=-250 and Guideline Y=900. This step
basically draws STM Element ID E1 (see Figure 15).
• Click on the intersection of Guideline X=-250 and
Guideline Y=900, and then click on the intersection
of Guideline X=250 and Guideline Y=900. This step
creates STM Element IDE2.
• Click on the intersection of Guideline X=250 and
Guideline Y=900, and then click on the intersection
of Guideline X=910 and Guideline Y=900. This step
creates STM Element IDE3.
• Click on the intersection of Guideline X=-910 and
Guideline Y=900, and then click on the intersection
of Guideline X=-250 and Guideline Y=0. This step
creates STM Element ID E4.
• Click on the intersection of Guideline X=910 and
Guideline Y=900, and then click on the intersection
of Guideline X=250 and Guideline Y=0. This step

creates STM Element ID E5.
• Click on the intersection of Guideline X=-250 and
Guideline Y=0, and then click on the intersection of
Guideline X=250 and Guideline Y=0. This step
creates STM Element ID E6.
• Click on the intersection of Guideline X=-250 and
Guideline Y=-600, and then click on the intersection
of Guideline X=-250 and Guideline Y=0. This step
creates STM Element ID E7.
• Click on the intersection of Guideline X=-250 and
Guideline Y=0, and then click on the intersection of
Guideline X=-250 and Guideline Y=900. This step
creates STM Element IDE8.
• Click on the intersection of Guideline X=-250 and
Guideline Y=900, and then click on the intersection
of Guideline X=-250 and Guideline Y=1500. This
step creates STM Element IDE9.
• Click on the intersection of Guideline X=250 and
Guideline Y=-600, and then click on the intersection
of Guideline X=250 and Guideline Y=0. This step
creates STM Element ID E10.
• Click on the intersection of Guideline X=250 and
Guideline Y=0, and then click on the intersection of
Guideline X=250 and Guideline Y=900. This step
creates STM Element IDE11.
• Click on the intersection of Guideline X=250 and
Guideline Y=900, and then click on the intersection
of Guideline X=250 and Guideline Y=1500. This step
creates STM Element IDE12.
• Click on the intersection of Guideline X=-250 and

Guideline Y=900, and then click on the intersection
of Guideline X=250 and Guideline Y=0. This step
creates STM Element ID E13.
• Click on the intersection of Guideline X=-250 and
Guideline Y=0, and then click on the intersection of
Guideline X=125 and Guideline Y=-600. This step
creates STM Element IDE14.
• Click on the intersection of Guideline X=-910 and
Guideline Y=900. Click on the intersection of
Guideline X=-900 and Guideline Y=1000. This step
creates STM Element ID E15.
• Click on the intersection of Guideline X=910 and
Guideline Y=900. Click on the intersection of
Guideline X=900 and Guideline Y=1000. This step
creates STM Element ID E16.
Figure 15 CAST Window Showing an STM Element and
Guideline Locations
(Click here to view a larger image)
Up to this point, we have finished drawing the geometry of
the Strut-and-Tie Model. Figure 16 shows how the CAST
window should look like now.
Figure 16 CAST Window after Step 2.2
(Click here to view a larger image)
Notes: When we draw an STM Element, STM Nodes are
automatically provided at each end of the STM Elements.
• Again, if you make a mistake, for example, you draw
an element at the wrong place, you can undo your
work by clicking the button from
the Standard toolbar or clicking Undofrom
the Edit menu.

• You can also move the position of STM Nodes by
clicking to switch to Modify mode (or by
selecting Drag STM from the Edit menu) and then
dragging the node. If the (Snap Boundary
Corners or STM Nodes to Grid Points) or the
(Snap Boundary Corners or STM Nodes to
Guidelines) option is turned on, the node will be
snapped to any Grid Points or Guidelines while
dragging.
• The Modify mode also allows you to move the
position of an STM Element by dragging the element
to the desired position. However, the connectivity to
the nodes at the ends of the element will be lost. If
the (Snap Boundary Corners or STM Nodes to
Grid Points) or the (Snap Boundary Corners or
STM Nodes to Guidelines) option is turned on, the
centroid of the STM Element will be snapped to any
Grid Points or Guidelines while dragging.
• Pressing the Esc key will terminate the Draw mode
and take you back to Select mode.
2.3 The next step is to assign bearing plates to STM Nodes we
have just drawn. Do the following:
 Click on the button from the Drawing toolbar to
be in the Select mode.
 Select STM Node IDs N12 (at X=-900 Y=1000)
and N13 (at X=900 Y=1000) by either clicking on
them or drawing a window completely around them.
The selected nodes will become star-type shapes as
shown in Figure 17.
 Click on the button from the Assigning toolbar

(or select Bearing Plates from theAssign menu).
The Assign Bearing Plates dialog box (Figure 18)
then appears. In this dialog box:
 Enter 600 in the Width text box.
 Enter 150 in the Length text box.
 Enter 25 in the Thickness text box.
 Click the OK button to confirm the input and close
the window.
After this stage, the CAST window will look similar to Figure
19.
Figure 17 CAST Window Showing Selected STM Nodes
(Click here to view a larger image)
Figure 18 The Assign Bearing Plates Dialog Box
Figure 19 CAST Window After Step 2.3
(Click here to view a larger image)
Notes:
• You are only allowed to assign bearing plates to STM
Nodes that are located on the Outer or Inner
Boundaries.
• To clear all selected nodes, click on the button
from the Selecting toolbar to be in the Select mode
and click on them. We can also clear the selected
nodes by selectingDeselect STM from
the Select menu, clicking on Point/Window, and
clicking on them (or drawing a window completely
around them).
• If the bearing plates do not appear on the screen,
click the button (or select Set Object View
Options from the View menu). After the Set Object
View Options dialog box (Figure 14) is displayed,

check Bearing Plates checkbox in the Structure
and Loading frame, and then click the OK button.
2.4 Now, let’s assign the Boundary Conditions, i.e., the Point
Loads and Point Supports, to the STM Nodes as follows:
• Click the button from the Drawing toolbar to
be in the Select mode.
• Select the previous selected STM nodes
(IDs E12 and E13; see Figure 19 for ID reference) by
either clicking on them or drawing a window around
them. This step can also be done by clicking
the button from the Selecting toolbar or by
clicking Restore Previous Selection from
the Select menu.
• Click the button from the Assigning toolbar
(or from the Assign menu, clickBoundary
Conditions). The Assign Boundary
Conditions dialog box (Figure 20) then appears. In
this dialog box:
 Click on Force option (radio) button.
 Enter -1005 in the text box next to
the Force radio button just clicked.
 Click the OK button to confirm the input and
close the window.
• Select all STM Nodes at the column bottom
(IDs N7, N9, and N11; see Figure 19 for ID
reference).
• Click again the button from
the Assigning toolbar. In this dialog box:
 Click on the Support radio button.
 Click the OK button to confirm the input and

close the window.
• Select the two STM Nodes at the column top
(IDs N8 and N10; see Figure 19 for reference).
• Click again the button from
the Assigning toolbar. In this dialog box:
 Click on Force radio button.
 Enter -3000 in the text box next to
the Force radio button.
 Click the OK button to confirm the input and
close the window.
At this stage, we have finished assigning Point Loads and
Point Supports to the STM Nodes.Figure 21 shows how the
CAST window should look like now.
Figure 20 The Assign Boundary Conditions Dialog Box
Figure 21 CAST Window after Step 2.4
(Click here to view a larger image)
Notes: You may assign Point Loads to STM Nodes that are
located on D-Region Boundaries (Outer or Inner) or in the D-
Region under consideration, but you are only allowed to
assign Point Supports to STM Nodes that are located on D-
Region Boundaries.
• If the Point Loads or Point Supports do not appear
on the screen, click the button (or select Set
Object View Options menu from the View menu).
After the Set Object View Options dialog box
(Figure 14) is displayed, check Point
Loads/Supports checkbox in theStructure and
Loading frame and click the OK button.
• Use the object size adjusters (the most
right one) located at the status bar to adjust the size

of Point Load and Point Support objects.
Obtaining Truss Forces
In this section, we analyze the model that we currently built to obtain forces in the STM Elements.
To analyze the model, click Run Design Calculations from the Analysis menu or click the button from
the Standard toolbar. A window displaying the analysis progress shown in Figure 22 then appears. After the analysis is
completed, the forces for each STM Element are shown in the display window (Figure 23). In the figure, compression
members are represented by dashed blue lines while tension members are represented by solid orange lines.
Figure 22 The Window Showing Analysis Progress
Notes:
• When there are multiple Load Conditions defined in the model, a dialog box will appear prior to the analysis
progress window, asking for Load Conditions to be analyzed.
• If you create a Strut-and-Tie Model which is not stable, an error message indicating that excessive loss of accuracy
occurred during the process will show up. To fix this problem, please follow suggestions described in Q & A #9.
Figure 23 CAST Window after Analysis is Performed
(Click here to view a larger image)
Defining and Assigning Properties
In this section, we define Strut/Tie/Node Property Types based on the forces we obtained from theprevious 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 Strutand Bottle-
Shaped. Click the button from the Defining toolbar.
Alternatively, click theDefine 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 Equationscombo 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/A615Mradio button.
• Now define each layer data by entering values in the
corresponding text boxes located in theBar 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 Definemenu (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