CASA Tutorial — Basic frame

Simple frame tutorial

This tutorial looks at building a basic frame, with the result of that shown in the video on the right.

We will look at various ways of entering and manipulating data. The aim is to explore the use of the program and try alternative techniques for the same situations with data chosen for the purposes of explanation rather than design correctness. Some of the techniques depend upon the version of CASA you are using; for example, the creation of the video requires the Enhanced edition or higher.

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The tutorial covers both how to build a model for analysis and also how to add cosmetic effects such as material textures and an advertising banner on the front of the building. The model remains perfectly analysable despite the cosmetic enhancements.

Contents
1 » Getting started11 » Interlude
2 » Setting titles12 » Member loads
3 » Conveniences13 » Splitting members
4 » Nodes14 » Loadcase combinations
5 » Members15 » Timber bars and advert banner
6 » Section types16 » Cameras
7 » Node supports17 » Analysing
8 » Replicating18 » Displaying graphical results
9 » More members19 » Displaying numerical results
10 » Another section type
Getting started

Firstly, load CASA (not the Reader version) either from a shortcut on the desktop or from the Windows Start Menu. Depending on your edition of CASA, some aspects of this tutorial may not apply. If using the Demonstrator version then the section generator and analysis parts will not apply.

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A main window will appear, in which a new empty model exists. This new model is untitled, unsaved, and contains only some default objects and settings.

While working through this tutorial, if you make a mistake then try using the Undo button on the main window toolbar.

On-line help is available in CASA through tooltips (hover over a field or button in a window to see a short explanation), through the “What’s This?” feature (click on the question mark in the window title bar and then click on the field or button of interest for more detailed information), and in the manual which can be accessed through the Help menu in the main window (requires a PDF viewer such as Adobe Acrobat Reader).

Settings titles

From the main window, open the Edit menu and choose Titles....

Enter some relevant titles and then close the window.

Conveniences

From the main window, open the View menu, choose Display Settings....

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There is a drop-down menu at the top of this window for selecting different pages of settings. On the page entitled Geometry & Loads (the first one; go through the drop-down menu if it is not visible), set the check-boxes beside the entries Node labels and Member labels.

This turns on the display of node and member numbers. Normally these are turned off so as to not clutter the view (and are often not needed due to the design of the interactive interface), but since this is a simple tutorial it is convenient to have them displayed.

When finished, this window can be closed.

While progressing through this tutorial, keep in mind that you can move around and in and out of the model by dragging the mouse and using the scroll wheel over the graphical view. A full list of mouse controls is given in an appendix in the manual.

Nodes

From the main window, open the Edit menu and choose Nodes....

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The window should be in its default state: the Name, Support, and Groups locks on red, the Name field is <new>, the “Default” group is chosen, and the input caret is in the X field.

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Now type 0 and press either TAB or Enter. A new node should be created with the name “1” and the caret should move to the Y field with the contents selected. In the main window you should see the node appear in the middle. Again, type 0 and press Enter, then do the same again for the Z field. The window should roll over to another <new> node and the caret move to the X field. Thus node “1” is defined as being at the coordinates (0,0,0) and we are ready to enter the next node.

Now define the next node at (10,0,0).

Now define the third node at (0,5,0).

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For the fourth node, with the caret in the X field, move the mouse pointer so that it is near node “2” on the model view in the main window. The node should be highlighted in orange and a little pop-up will appear to the effect of node 2 at coordinate (10,0,0) in the “Default” group. Click with the left mouse button. The number 10.000 (the X-coordinate of node 2) should appear in the X field and the caret should move to the Y field Here we have interacted with the model view to copy information from a pre-existing object to help us define a new object. Now use the mouse to set Y to 5 by clicking on node 3. The value of Z has already defaulted to 0, so we can keep this by just pressing TAB or we can copy the value from another node by clicking on that node.

Now define the fifth node at (5,7.5,0).

If you wish, this window can now be closed.

Members

From the main window, open the Edit menu and choose Members....

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The window should be in its default state; the Name, Releases, and Groups locks on red, the Name field is <new>, the “Default” group is chosen, and the input caret is in the Node A field.

Define the first member as going between node 1 (node A) and node 3 (node B) by clicking on the nodes.

For the Maj. Axis (major axis, e.g. the one to which the web of a typical I-beam would be aligned) there are two fields next to each other. In the left-hand field either type Z and press Enter or open the drop-down menu and choose Z. This aligns the major axis with the global Z axis. The right-hand field is used to specify a node when the axis points towards a node; it is not used in this example and so can be ignored.

Ordinarily, when entering data by pointing-and-clicking, the caret is automatically moved to the next field, but when choosing from the drop-down menus the caret remains in the field, so now either press TAB or Enter or click on the Section field and type in Column and press Enter. A message box will pop up informing you that a section type has been created. We will define the properties of this later. Click OK to remove the message. The caret will remain in the Section field after the message, so press TAB or Enter to roll over to another new member.

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You will notice that there are red crosses beside the member name and the section type. This indicates that they are not adequately defined for the purposes of analysis. While the member itself is fully defined, it is dependent upon the as-yet undefined section Column, and so the member is marked too. As we progress through the tutorial and complete the definition of the section type then these crosses will disappear.

Define the second member as going between nodes 2 and 4 by clicking on the nodes. As this is to be a counterpart of the first member, click on the first member to copy the definitions for the Axis and Section (i.e. Z and Column). After the section value has been copied, the window will roll over to a new member.

For the next member, make it span between nodes 3 and 5, with an Axis of Y and a Section of Rafter.

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For the fourth member, make it span between nodes 5 and 4 with the same axis and section as the previous member.

If you wish, this window can now be closed.

Note that the section types used so far have been created but not defined, so CASA cannot fully render the section shapes. Instead, simple thin lines are drawn with a small “tick” mark halfway along. The tick indicates the directions of the major and minor axes of the member. When we define the section types later the members will become fully rendered.

Section types

To open the section type editor you could use the same method as for the other editing windows — from the main window, open the Edit menu and choose Section types... — but we will use a different technique this time: in the main window, point to member 1 so it is illuminated and click with the right-hand mouse button to open a menu. From this menu go to the Edit other submenu and choose SectionType Column. This will open the section type editor and display Column ready for editing.

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For the Column type, ignore the material for the moment and open the Library menu in the Geometrical properties tab. Scroll down, open the GB-UC subsection by double-clicking on its name, scroll down and choose GB-UC 356×406×235. The property fields will be filled in, the shape set to I, and the material automatically set to Steel. If a different material is desired then it can be changed independently.

Now go the Name field in the window and from the drop-down menu choose Rafter. Choose the GB-UB 356×171×45.

If you wish, this window can now be closed.

Node supports

From the main window, open the Edit menu and choose DOFs....

DOF stands for “Degrees Of Freedom”, and the same definitions are used for both nodal supports and member end releases. There are a few of the most useful support and release types predefined. From the Name menu choose “Pinned support”. Looking at the row of checkboxes in the window, it should be apparent that this support is restrained along the linear X, Y, and Z axes but free to rotate about each of those axes.

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Now drag the icon depicting a support (without a cross) on to the model view and hover over node 1. The node should be illuminated; if a member illuminates then you are pointing more to the member than to the node, so move the mouse nearer to the node until the node illuminates. Release the mouse button to drop it onto node 1. Then drag the same icon again, but this time onto node 2. In the model view, nodes 1 and 2 should now have purple circles indicating the presence of restraints.

If you wish, this window can now be closed.

Replicating

From the main window, open the Select menu and choose Manipulate... to open a selection window.

With the Selection window having the input focus (click on it if you are unsure), click on each of the members in the main window model view with the left mouse button to select them all. If you make a mistake, such as clicking on a node, you can deselect it by clicking on it again with the SHIFT held down.

If the graphical view is too small or at a bad angle then you can drag it with the mouse and use the scroll wheel to move in and out. Dragging with the left mouse button will rotate; with the right it will pan.

Now in the Selection window, in the Summary tab, click on the button marked Auto-select (for copying). This will select the nodes between which the members span. In the counts frame there should be an indication of 5 nodes and 4 members selected.

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Now in the same window, go to the Transreplication tab. This is where translation, rotation, and replication can be applied to nodes with associated selected objects (such as members or loads) being adjusted or copied accordingly. Open the Translation menu and pick Translate by offset. In the X, Y, and Z fields enter 0, 0, and 5, respectively.

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At the bottom of the window is a field indicating Number of copies. Change this value to 1.

Now click the button marked Transreplicate. A copy of the frame should appear five metres behind it in the model view.

Go back to the Summary tab and click the button marked Clear to remove the selection.

If you wish, this window can now be closed.

More members

If you had closed the member window before then from the main window open the Edit menu and choose Members....

The window will normally open at a new member. If not at <new> then open the Name menu, scroll to the bottom, choose <new>, and then put the caret into the Node A field (either with the mouse, or press TAB or Return).

We are going to create three members joining the roof nodes of the front frame to the back frame. It may be necessary to rotate the view to better see the nodes. The input focus should remain in the member editing window after dragging the view around, but if you click outside of CASA then you may need to click on the Node A field in the member editing window before continuing.

Define a member between node 3 on the front frame and node 8 (its corresponding rear-frame node) with an axis in Y and a new section of Beam. After removing the message box indicating that a new section type has been created, instead of moving directly to the next member, click on the green locks for Axis and Section to turn them red. Now put the caret into the Section field and press TAB to move to the next, new, member.

Now define the next two roof members, one along the peak between nodes 5 and 10, and the other along the side between nodes 4 and 9. Notice how the locks keep the same axes and section for these two members without them having to be specified each time.

If you wish, this window can now be closed.

Another section type

Open the section type window again, either from the Edit menu or by pointing to member 9 and choosing Edit other — SectionType Beam. Make sure that the window is showing the Beam type.

Enhanced (or higher) editions only:

For the Beam type we will use the section generator. Open the Generator tab and in the drop-down menu choose Open section. Eight dimensions define the three plates of the section. The overall depth, D is to be 352mm. Then the top flange, w1 and t1, is 171×9.7mm respectively. It is central on the web, so the distance x1 is 171/2 = 85.5mm. The web thickness, t2 is to be 6.9mm. The bottom flange is the same as the top flange, so w3×t3 is 171×9.7mm and the offset x3 is 85.5mm. Now click on the button marked Set.

In the Section properties tab, choose a shape of I, and in the Material properties frame choose Standard Steel from the drop-down menu.

The dimensions entered for Beam are the same as the dimensions of the UB 356×171×45 used for Rafter. It can be seen that even though the section generator ignores fillets and toes, the results are close to those of the library section.

All other versions:

In the Geometrical properties panel, open the Library menu and choose GB-UB 356×171×45

Interlude
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If you now use the mouse to move in and rotate the structure view you will see the elements rendered as beams in a steel-grey colour. The illumination always comes from the viewer’s position so that the side being looked at is never in shade.

To double-check the entered data, simply point the mouse pointer at the nodes and members and look at the pop-up information. For example, point to the right-rear base, node 7, and see that it is located at coordinates (10,0,5) with a pinned support in group “Default”.

If you find any mistakes then try pointing at the erroneous item with the mouse, clicking with the right-hand button, choosing Edit..., and making the corrections.

At this point it is probably worth saving our model.

Not applicable to Demonstrator edition

From the main window open the File menu and choose Save as.... There is a standard file dialogue window from where you can enter a filename and choose where to save the file. Typing “.casa” on the end of the filename is optional; if it is omitted then CASA will add it for you.

Member loads

We will now add some loads to the roof beams, so rotate the structure view such that the three of them are clearly visible.

From the main window, open the Edit menu and choose Member loads....

The first load will be applied to member 9. Following previous examples, this can be done by ensuring the input caret is in the Member field and using the mouse to click on the member in the structure view. Alternatively, open the drop-down menu of the Member field and choose 9. When picking from the menu, the caret will not automatically advance to the next field, so press TAB or Enter to move.

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We will be entering uniformly distributed loads, so open the drop-down menu for the Shape field and choose UDL.

Put the caret in the Fy-A (linear force in Y at end A) field by clicking on it, enter -10 and press TAB or Enter. The setting of the Shape to UDL ensures that the force at end B automatically matches that at end A.

Continue for the other fields so that both Fy-A and Fy-B (linear force in Y at end B) have the value -10 and the others are all 0.

Note that this load has its Axes in the default global direction, so Y is relative to global coordinates irrespective of the orientation of the member, and it is a member of the Default loadcase.


We now wish to copy this load onto members 10 and 11, so we will select these members. We could do this through the selection editing window, as before, but for this exercise we will do it directly without the selection editing window by simply pointing at the members with the mouse and doing a CTRL+Left-click. The members should appear highlighted in red.

Alternative method of making a selection: Open the section type editing window and choose Beam. Then open the context-sensitive menu, go to the selection submenu, and choose Add all related members to the selection.

Go back to the Member load dialogue window and make sure it is displaying load 1. Open the context-sensitive menu with a right-click of the mouse over the window background, go down to the Selection submenu and choose Copy onto selected members.

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Alternative method of copying loads: with the member load dialogue window showing load 1, simply drag the icon depicting a member load in the top-right of the window across onto members 9 and 10 in the main window, similar to applying supports. There is no need to make any selection with this method.

This gives us our three loads across the roof. Now in the Select menu in the main window, choose Clear.

If you wish, this window can now be closed.

Splitting members

Let us assume that we wish to have nodes at the midpoints of each member.

Open the Selection dialogue window (Select — Manipulate... menu in the main window), and in the Summary tab make sure that at least Members is ticked (it does not matter what else is or is not selected for this operation). Now click on the button marked All (filtered). The whole structure will be highlighted red with the selection.

An alternative method, which can be tested, is to ensure that all of the model is visible in the main window and then while holding the CTRL key down, drag with the left mouse button to create a rubberband around the whole structure. When the mouse button is released, everything will be selected. Creating a rubberband with CTRL and the right-hand mouse button instead will remove everything from the selection, which can also be tested. Remember to click on All (filtered) when you are finished experimenting, to ensure that everything is indeed selected.

Now open the Selection window context-sensitive menu (right-click with the mouse in the Selection window), go down to the Split members submenu and in the Fragments tab accept the default of 2 fragments and click on the button marked Split.

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The selection can now be cleared by clicking on the button marked Clear in the Selection window.

It should now be seen that every member in the structure has been split in half with new nodes at the midpoints of the original members, and the loads have been split accordingly.

The selection window can now be closed.

Loadcase combinations

For this tutorial we only have one loadcase but we wish to have a combination of both those loads and gravity.

From the main window Edit menu, choose Combinations.

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In the Name field, enter Default + Gravity, and press Return. Now tick the boxes associated with the loadcases Default and Gravity in Y. Change the value of the factor associated with the Default loadcase to 2.00 by clicking on the number in the factor column and typing in 2 and pressing Enter. (Note that you have to tick a loadcase before you can edit its associated factor.)

Gravity is automatically calculated according to the lengths of members, the density of their material, and g = 9.81 m/s2.

If your version supports Second Order (aka “P-delta”; non-linear) analysis then using it is as simple as just ticking the box marked Second Order, that’s all. Later on you can try setting this and comparing the results from the analysis.

If you wish, this window can now be closed.

Timber bars and advert banner

Open the Groups editing window. Create a new group called Timber. Set its usage to Annotation from the usage menu. Set the member colour to a solid woody colour by clicking on the Member colour button, choosing a suitable colour, and ensuring that Alpha is set to 255 (this means the colour is fully opaque; a value of 0 would be fully transparent). Click Ok. Now in the texture menu choose Texture: timber.

Create another group called Advert in the same way, but make it solid white and use the image of “Intesym logo”.

Now create two nodes in the Timber group at coordinates (3,5,0) and (7,5,0). These should be nodes 28 and 29.

Now create two members in the Timber group spanning between nodes 3 - 28 and 29 - 4, both with their axes in Y and specify a new section type called Bar.

Now create a member in the Advert group spanning between nodes 28 and 29 with its axis in Y and give it a new section type called Sign.

Now open a section type editor and choose Bar. As we are only concerned with the visual effect, not the structural properties, it is okay to choose a large RHS like a 300x200x6.3.

Now edit the section type Sign. Again, only the visual effect is important, so manually choose a shape of Rectangle and set the Depth to 1000 and the Width to 1.

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Now close the section type and member windows, turn off any node or member labels, zoom into the structure and move around and inspect the wooden beams and company logo.

This model will still analyse because the timber members and advert are in groups marked as being for annotation only, and so they are completely ignored during the analysis.

Cameras

To create a camera flight we need to set up nodes along the flight path to define the trajectory.

Open the node editing window again and, if necessary, set the Name field to <new> from the drop-down menu.

To help keep the camera nodes distinct from other nodes we will give them names instead of simple pure numbers. For this, disable the lock (red box) next to the Name field by clicking on it to turn it green. Doing this means that each time you complete the definition of a node and the window rolls over to <new>, the input focus will appear in the Name field, making it easier to enter a name manually.

Even with the Name field unlocked, if you skip entering a name and start defining a new node then a new number will be allocated automatically, the same as when the field is locked. The purpose of the lock is to implicitly skip entering a name to simplify the process of entering nodes when the specific names or numbers are unimportant. In the following instructions, if you accidentally enter a node with an automatically generated number instead of the intended name then you can correct this by opening the context-sensitive menu (right-click over the node editing window), going to the Rename submenu, and entering the intended name and pressing Enter.

In the Name field enter F1 and press TAB or Enter. This will create a new node called “F1”. In the Groups field, check the box for Camera Focus 1 and uncheck the box for Default. If a pinned support has been carried over from a previous node (because the input lock is red) then open the support menu and change it to <none>.

Now set the coordinates of this node to (5, 5, 2.5).

Now create another node called C1 exclusively in the Camera Path 1 group. Set this node at coordinates (5,10,-25).

Now create a further three nodes called C2, C3, C4, and C5 at coordinates (-30,0,2.5), (5,10,30), (40,20,2.5), and (5,10,-25), all exclusively in the Camera Path 1 group. The node C5 is in the same place as C1, making the camera finish where it starts.


Now from the main window Edit menu choose Cameras....

In the Name field, type in Flight and press TAB or Enter.

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There is a drop-down menu entitled Type. From this menu, choose Dynamic.

Then from the drop-down menus for the Along group and Looking at group, choose Camera Path 1 and Camera Focus 1 respectively.

In the Period per node field, change the value to 3.0.

In the toolbar of the main window, open the Camera drop-down menu and choose Flight. The view will move to the start position of that camera. Click on the Run camera button next to the menu.

The view will now fly around the structure and should look similar to the animation at the start of this tutorial.

The flight can be stopped mid-stream by changing to camera <none>, or the speed altered by using the mouse scroll-wheel as a jog control.

Try adding and changing nodes in the Camera Path 1 and Camera Focus 2 groups to change the paths along which the camera both moves and looks.

Analysing

Not applicable to Demonstrator edition

From the main window Analysis menu, choose Analyse.... A window opens with a panel and a button marked Analyse. Click on the button to start the analysis. A progress report and any warnings will appear in the panel.

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If your version supports the determination of natural modes of oscillation then obtaining these is as simple as just ticking the box marked Natural modes. The first three modes of oscillation (lowest frequencies) are available by default and more can be requested through the main window menu of Edit - Natural Modes....

At the end of the report, the words “Analysis succeeded” should be there in green. If a message is given in yellow or red then please go back and review the input data for errors.

This window can now be closed.

Demonstrator:

The Demonstration CD contains this tutorial, pre-analysed, which can be loaded and used from this point on.

Displaying graphical results

From the main window View menu, go to the Combinations submenu and check the box next to Default + Gravity. The default selection of nodal displacements, member deflections, and nodal reactions will appear. Pointing to the displaced nodes and reactions with the mouse will provide the relevant results in a pop-up box.

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If the displacements are small or the reactions large then from the main window View menu, choose Display settings... and adjust the scale factors.

Turning off the loads and labels will give a clearer view. Try looking at the bending moments and shear-force diagrams too.

Displaying numerical results

From the main window Results menu, choose Statics... to open the static analysis results.

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The window will automatically default to displaying combinations, so our Default+Gravity should be already chosen and the table showing the Member End Forces.

There are four tabs, containing tables for member end forces, nodal displacements, nodal reactions, and a detailed individual member display.

As you move the mouse pointer over the table you will see the relevant nodes and members highlighted in the structure view in the main window. In addition, pointing and clicking on a node or member in the main window while a results viewer has the input focus will cause the relevant lines in the table to be highlighted.

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For example, with the results viewer having the input focus (click on it if you are not sure) and the table showing the member end forces, move the mouse over the structure view in the main window and point at and click on member 10. The two lines pertaining to member 10 will be highlighted and the table will scroll so they are visible. The final column, Stress should read 2.778 and 92.489 for each end respectively (if you used the section generator data for section type Beam). If your values are different then check the combination load factors first, then other data such as section types and nodal coordinates.

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