1. Introduction

2. Demo of a sample problem

• Problem Statement
• Set Units
• Build Model
• Compute
• Save structure

3. Functions Available

File

• New
• Open
• Overlay
• Save
• Download from Server
• Overlay from Server
• Save to Server
• New StructureXML
• Edit StructureXML
• View StructureXML
• Exit

Graphics

• Pan
• Zoom
• Grid
• Scale
• View Node Numbers
• Ortho
• Snap to Grid

Function

• Add Member
• Enter Member Properties
• Constrain Node
• Load Node
• Edit Node Coordinates
• Remove Member
• Remove Constraints
• Unload Node

Compute

• View Stiffness Matrix
• Member Forces
• Reactions
• View Displaced Structure
• Text Output

4. StructureXML

• Benefits of using XML
• About StructureXML

Trussworks allows users to easily create and analyze 3D Structures using the Direct Stiffness Method. It models truss structures that can carry axial loads loads.  The click and drag interface lets you input two-dimensional structures, but the program can take in and perform calculations for three-dimensional structures as well using a text based XML input (see Section 4).  Also included is a database of steel cross-sections and their corresponding geometric properties developed by a colleague and adapted for the programs, as well as material properties of the most commonly used engineering materials.

The program is intended to be free to use, the primary target audience being undergraduate engineering students and faculty. The program, and source code, as well as the documentation, can all be downloaded free of cost. The authors' intend this to be an "open source" product, available for modification and expansion to suit any user's needs. While there is no limit to the number of nodes and members that might be modeled, it is not intended to function as industrial strength programs for structural engineering professionals - but it may be of use to the latter in preliminary design. Trussworks can be run both as an application on a users local machine, or as an applet on any web-browser.

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Problem Statement

Using Trussworks, model the structure shown in Figure 2.1 .  All members are made of carbon steel, and use the W130x24 cross-section.  Report the deflections at node 1, the reactions and node 0, and the member forces in member 0-1.

Figure 2.1 - Sample truss to be modeled

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Set Units

The first thing that is seen on starting the programs is the dialog box in Figure 2.2 . This allows you to pick the units that you will be using for your structure, as well as the initial screen dimensions and the grid spacing. The grid spacing is also the snap resolution used in the program. Both the screen dimensions and the grid spacing can be changed later at any time using the Zoom and Set Grid Spacing functions. Once the units have been set, the only way to change them for the same structure is by editing the StructureXML text.

Figure 2.2 Dialog box to set units and initial dimensions

Pick the “KiloNewtons/meters” option, and input a Length of 6 meters, and grid spacing (snap resolution) of 1 meters.

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Build Model

• Add Members - Go to the “Function” menu, and select “Add Member”.  Click once to add the first node of the member, move the mouse, and click again for the second node.  Repeat the process until you have a structure like that shown in Figure 2.3.  Alternatively, you can copy and paste the text from demoStep1.xml into the text area from selecting "File" à  "New StructureXML" to get to this step.

Figure 2.3 - Members added

• Enter Member Properties - Once all the members have been added, enter their member properties.  In this example, all members are W130x24 and made of carbon steel.  From the “Function” menu, select “Enter Member Properties”.  This will bring up the window shown in Figure 2.5 .  From the drop down menus on the right hand side, select the “W” section, and then select “W130x24”.  Next, select “CarbonSteel” from the drop down menu on the bottom right.  Select the “Apply to all members” option (default option), and click on the “Apply” button.  Alternatively, you can copy and paste the text from demoStep2.xml into the text area from selecting "File" à  "New StructureXML" to get to this step.

Figure 2.5 - Member Properties Panel

• Constrain Node - To constrain a node, select “Constrain Node” from the “Function” menu.  This will bring up another window as shown in Figure 2.6 .  Next, click on the nodes to be constrained on the main screen.  Selected nodes will be highlighted in blue.  Then check the directions the nodes to be constrained, (in this example, check all displacements), and click on the “Constrain” button.  The constrained nodes should be drawn in yellow, as shown in Figure 2.7.  Alternatively, you can copy and paste the text from demoStep3.xml into the text area from selecting "File" à  "New StructureXML" to get to this step.

Figure 2.6 - Constrain Nodes Panel

Figure 2.7 - Nodes Constrained

• Load Nodes - To apply a load on a node, go to the “Function” menu, and select “Load Node”.  This will bring up the window shown in Figure 2.8 .  Next, go back to the main window and click on the nodes to be loaded.  Selected nodes appear highlighted in blue.  Then input the loads to be applied (in our case 5000 kN in the negative y direction), and click on the “Load” button.  The nodal loads should appear on the main screen as shown in Figure 2.9.  Alternatively, you can copy and paste the text from demoStep4.xml into the text area from selecting "File" à  "New StructureXML" to get to this step.

Figure 2.8 - Load Nodes Panel

Figure 2.9 - Nodes Loaded

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Compute

• View Displaced Structure -  To view the displayed structure due to the applied loads, select “View Displayed Structure” from the “Compute” menu.  Different magnification factors may be chosen to properly view the displayed structure.  In this case, select “View Displayed Structure à x1”.  This will show the displacements magnified by a factor of 1 shown below in Figure 2.10 .

Figure 2.10 - Displaced Structure

• View Member Forces - To view the forces developed in the members as a result of the loads applied, select “Member Forces” from the “Compute” menu.  Click on a member to view its forces, and a new dialog-box will pop up showing the member forces (Figure 2.11).  In our case, click on member 0-1.

Figure 2.11 - Member Forces Panel

• View Reactions - To view the reactions at the constrained nodes due to the applied loads, select “Reactions” from the “Compute” menu.  This will compute the reactions and display them on the main screen.  If the numbers look crowded, use the “Zoom à Window” option from the “Graphics” menu, and zoom in on the node.

Figure 2.12 - View Reactions

• Text Output - To view the results of the computations in a text format, select “Text Output” from the “Compute” menu.  This will bring up a window with the text output of the computations as shown in Figure 2.13.  If running the programs as an application, select “Save As…” from the “File” menu in the text window, which will allow the user to save the text output on the local hard-drive.  If running the programs as an applet, highlight and copy all the text from the text area, and paste it in any text editor.  This will allow the results to be saved on the local machine.

Figure 2.13 - Text Output of results

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Save Structure

• If running the program as an application, select “Save” from the “File” menu to save the structure in binary format on the local hard drive. The saved structure can be retrieved later by selecting “Open” from the “File” menu.
  
  To save the structure in the StructureXML text format, select “View StructureXML” from the “File” menu. This will bring up the StructureXML text window. Next select “Save” from the “File” menu to save the XML text on the local hard drive.
  

• Running the program both as an applet and as an application let’s you save your structure to the server over the Internet. Select “Save to Server” from the “File” menu. This will upload the structure in binary format to the server running the applet. The file can later be retrieved by selecting “Download from Server”.
  
  To save the structure in the StructureXML format when running as an applet, select “View StructureXML” from the “File” menu. This will bring up the StructureXML text window. Next, select “Select All”, followed by “Copy” from the “Edit” menu and paste the copied text to any text editor and save it on the local hard drive. To retrieve a structure from the XML later, open the XML text using any text editor, copy the StructureXML, and paste it on the text window from the “New StructureXML” option in the “File” menu and hit the “OK” button.
  

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The functionalities available in Trussworks can be broken into four main groups, which are simply the menu items that are present in the program.

File

Figure 3.1 - File Menu Functions

• New - Creates a new structure and clears the old structure from memory.
• Open - Opens a structure saved in binary format from the users hard drive.  Not available when running as an applet.
• Overlay - Overlays another structure saved in binary format from the users hard drive onto the existing structure. The program increments the node numbers of the second structure with the number of nodes present in the first structure. Not available when running as an applet.
  This would allow, for example, different users to work on different parts of a structure. Once the parts have been created and saved, they can all be overlaid to form the whole structure.
• Save - Saves structure in binary format on users hard drive.  Not available when running as an applet.
• Download from Server - Downloads structure saved in binary format in a server over the Internet using TCP.  Applets can only download structures from a server that has the same host name as the web server from which it originated.
• Overlay from Server - Overlays another structure saved in binary format by downloading the second structure from a server over the Internet using TCP.  Applets can only overlay structures from a server that has the same host name as the web server from which it originated.
• Save to Server - Saves structure in binary format to a server over the Internet using TCP.  Applets can only save structures to a server that has the same host name as the web server from which it originated.
• New StructureXML - Starts a new StructureXML document (see Section 4).  If running the programs as an application, then File à Open opens a dialog box that lets the user open a text (XML) document from their hard drive.  Users running the program as an applet can copy a StructureXML text from a local file, and paste it on the textarea.
• Edit StructureXML - Lets the user edit their structure as a text (XML) file.
• View StructureXML - Lets the user view their structure in the StructureXML format.  If running as an application, File à Save lets the user save the structureXML document in their hard drive.  Applet users who want to save the StructureXML text must highlight all the text in the textarea, copy it, and then paste it on a text editor to save it on their hard drive.
• Exit - Closes the program and clears the structure from memory.

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Graphics

Figure 3.2 - Graphics Menu Functions

• Pan - Allows the user to “pan” or move a structure around the screen by clicking and dragging the mouse.
• Zoom - 
  • Window – Zooms in on a structure, in the rectangle created by clicking and dragging the mouse on the screen. 
  • Out – Zooms out by a factor of 0.5x. 
  • Extents – Zooms to fill the full screen with the structure.
• Grid - 
  • On – Lets the user turn on, or turn off the grid lines.
  • Set Grid Spacing – Allows user to explicitly set the grid spacing.  This is also the “snap to grid” resolution used by the program.
• Scale - Toggles the scale visibility to on or off.
• View Node Numbers - Toggles node numbering to on or off.  The node numbering can be turned off, if for example, the structure gets large and the node numbers start cluttering the screen.
• Ortho - Toggles ortho mode to on or off.  When in ortho (orthogonal) mode, the user will only be able to draw horizontal and vertical members.
• Snap to Grid - Toggles snap to grid mode to on or off.  When in snap to grid mode, the start and end of members created by clicking the mouse will snap to the grid lines.

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Function

Figure 3.3 - Function Menu Functions

• Add Member - Adds a member by clicking the mouse twice.  The first click records the first node coordinates, and the second click records the second node coordinates
• Enter Member Properties - Brings up the Edit Member Properties window (Figure 3.4), which allows the user to enter the member properties for the structure. The user can set values for the member properties for all the members at once by selecting “Apply to all members”, and after setting the member properties, clicking on the “Apply” Button. To set values member property values for individual members, first select “Apply to selected members” after setting the values. Next go back to the main screen and click on the members you want to select. Selected members appear blue. 

Figure 3.4 - Enter Member Properties Window

This window lets the user set values for the cross-sectional area and the modulus of elasticity.  Clicking on the “Find a Section” button brings up the window shown in Figure 3.5.  This window allows the user to compare two cross-sections, and also has the functionality to match the section on the right with the section on the left based on the largest section modulus.

Figure 3.5 - Find Section Window

The sections database can also be queried by selecting "Search Sections" in the "options" menu.  This will bring up the subpanel shown in Figure 3.6.  Here the user can input any known parameters, and all possible matches will be shown on the panel.  Finally, clicking on the "Select this Section" button will select the section and go back to the "Enter Member Properties" window.

Figure 3.6 - Search Section Subpanel

• Constrain Node - Allows the user to constrain nodes. Trussworks brings up the window shown in Figure 3.7 , and lets the user constrain nodal displacements in the x, y, and z directions.

Figure 3.7 - Constrain Node Window

• Load Node - Allows the user to load nodes. Nodes are selected by going back to the main screen and clicking on the nodes to select them. Selected nodes have a blue box drawn around them.  The window shown in Figure 3.8 appears which lets the user apply nodal forces in the x, y, and z directions.  These forces are in the global coordinates.

Figure 3.8 - Load Node Window

• Edit Node Coordinates - Allows the user to change node coordinates. This can be done in two ways:
  • Click and Drag Node – This option lets the user change a node coordinate by clicking on a node to select it, and then clicking again to set the new coordinates. 
  • Text Input – This option lets the user change the node coordinates by typing the new coordinates. First select this option, and then click on any node.
• Remove Member - Allows the user to remove members from the structure.  Select this option, and then click on a member to remove.
• Remove Constraints - Allows the user to remove any nodal coordinates.  Select this option, and click on a node to remove its constraints.
• Unload Node - Allows the user to unload a node.  Select this option, and click on a node to unload.

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Compute

• View Stiffness Matrix - This option brings up a window that displays the stiffness matrix of the structure.
• Member Forces - Computes the internal member forces that exist on a structure.  Select this option, and then click on any member to view its internal forces.
• Reactions - Computes and displays the reactions on the screen for the constrained nodes.
• View Displaced Structure - Computes the nodal displacements, and shows the displaced structure on the screen. 
  • X1 – Shows exact displacements, i.e. Scale factor = 1. 
  • X10 – Magnifies displacements by a factor of 10. 
  • X100 – Magnifies displacements by a factor of 100. 
  • X1000 – Magnifies displacements by a factor of 1000.
  • Scaled – Magnifies displacements by an appropriate scale to properly view displacements. 
• Text Output - Opens a window that lists the reactions, member forces, and displacements of the structure.

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Benefits of using XML

In some instances, it may be more convenient to create the structure using a text input file, or in the form of a spreadsheet. For example, if the number of members is large, the click and click interface may prove to be cumbersome. Or in the case of a three dimensional truss, a text based input may be the only choice. 

StructureXML not only fills this need, but it can also serve as the middle ground for communication between Trussworks and another program. A developer can, for example, create a graphics package that displays the structure by interfacing with the StructureXML text data without needing to know about, or have access to, the many classes that make up a Truss object.

XML provides another method of storing the structure in addition to the binary format. Since these are simply text files, they carry further advantages. For instance, these text files can be very easily copied and pasted while running the programs as applets, or the text can be emailed without the need for attachments.

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About StructureXML

StructureXML, as all XML documents, needs to be both well-formed, and valid.  This simply means that -

• For a well-formed document, the start tag must be ended by an end tag. It must also contain the prolog and the document element (also known as the root element).
• A valid XML document has two additional requirements to that of a well-formed document. First, the prolog of the document must include a proper document type declaration, which contains a document type definition (DTD). Second, the rest of the document must conform to the structure defined in the DTD.

The DTD for StructureXML is defined in Table 4.1 . All StructureXML documents must have this at the beginning of the text file.

Table 4.1 - DTD for StructureXML

The body of a sample StructureXML document is listed in Table 4.2 . This XML document creates a two member structure that is constrained on two nodes, and loaded on the third node as shown in Figure 4.1. Notice that this conforms to the DTD listed above in Table 4.1. For example, the DTD declares – “<!ATTLIST units length (meters | centimeters | feet | inches) #REQUIRED …>” which is satisfied by the text below that says “<units length = "meters" force = "kiloNewtons"></units>”.

Table 4.2 - StructureXML for a two member truss

Figure 4.1 - Structure produced from StructureXML using Trussworks

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