Newsletter Archive:  Did You Know?

Did You Know?


Due to the overwhelming popularity of the 'Did You Know' snippets featured in various issues of News.St7, we have placed them all here so you can easily access them from one centralised location.

    0001: Dynamic Scaling
    0002: Ctrl-Click the Entity Show/Hide Toggle
    0003: Shear Centres of Beams
    0004: Transparent User Stress Limits
    0005: Shortcut to Selection Arrow
    0006: Applying Attributes
    0007: Ctrl-Click Edit Nodes
    0008: Right-Click Attributes
    0009: Verification Manual
    0010: Subdivide only Normal Beams
    0011: Brick Cutting Plane Animations
    0012: Auto-Assign Restraints
    0013: Ctrl-Click Retrieve
    0014: Run Time Improvements
    0015: Strand7 Viewer
    0016: Edit-Delete-Attributes
    0017: Animations in Powerpoint
    0018: Summary-Information
    0019: Length-Area-Volume Loads
    0020: Draw Ply Axes
    0021: Hide Zeros
    0022: Whiteboard
    0023: Nonlinear Convergence Graph
    0024: View Load Factors
    0025: Anchoring Node Coordinates
    0026: Background Image
    0027: Numbered Backups
    0028: Select Brick or Plate Faces
    0029: Plate and Brick User Contour
    0030: Skip Transitioning
    0031: Browse...
    0032: Middle Button for Dynamic Rotate
    0033: User Contour of Principal Stress with Largest Magnitude
    0034: Perspective in 3D Drawing
    0035: Beam Local and Principal Results
    0036: Selecting All Entities Behind the Selection Box
    0037: Geometry Creation in Strand7


0001: Dynamic Scaling
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With results open press F4 to enter the dynamic view environment.

You can dynamically increase or decrease the Displacement Scale of deformed models by clicking Scale in the Dynamic Rotation toolbar (shown) and holding the left mouse button while moving the mouse: up to increase and down to decrease the displacement scale. When an appropriate scaling factor is obtained, click OK. This will automatically set the displacement scale to the desired value.

Shortcut
The Scale option can be quickly accessed (while performing any of the other dynamic functions - ie Auto, rXY, rX, rY, rZ, Zoom and Pan), simply by pressing and holding down both the Ctrl key and the left mouse button and following the procedures explained above.

0002: Ctrl-Click the Entity Show/Hide Toggle
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Normally, by clicking the show/hide toggles, the model window automatically updates and redraws to effect the changes. Often we need to turn on/off more than one entity and for large models this can take time when redrawing after each selection. Instead, hold the Ctrl key while clicking the entity toggles to prevent Strand7 from redrawing after each click. When finished select redraw to refresh the screen. (F3 or F5)


0003: Shear Centres of Beams
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By default, Strand7 beam elements are positioned such that the element's nodes coincide with the section's centroid. In sections such as C-sections, where the shear centre is not located at the centroid, significant twisting displacements will be generated due to lateral (shear) loads. If your structure is constructed in such a way that this twist is restrained, due to the load passing through the shear centre, you can offset your section such that the nodes are located at the shear centre of the section. You can do this automatically with the Auto Assign Beam Offsets tool.

0004: Transparent User Stress Limits
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If you're interested in the sections of your model that exceed the design limit, you can contour your results such that anything outside the defined limits is transparent. This makes it easier to check complex internal components without having to manually hide outer elements.

In Results/Settings under the Style tab clear the < Min and > Max options. Now, under the Limits tab, set the user defined limits to a minimum value of say the design limit and the maximum to the maximum calculated. Only those elements with stress over the allowable limit will be contoured with the rest of the model being transparent.

0005: Shortcut to Selection Arrow
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Have you ever tried to select an element only to discover that the entity selection arrow is not active?

Well, there is no need to use the mouse to toggle the arrow. Simply press the space bar.

With Release 2.3 single key shortcuts are also available to toggle the entity selection buttons:
node, beam, plate, brick, link, vertex, geometry.

0006: Applying Attributes
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When applying attributes to an element, for example Beam Rotational End Releases, selecting the beam before opening the attribute dialog box will apply the release to both ends.

But, what if you only want the release at one end?
There is a simple solution. Before selecting the beam, bring up the required dialog box. Now select the end of the beam you want to apply the release to and you will find that only half the beam is selected. Only this end will be assigned the attribute. Strand7 uses this approach for the other attributes, such as brick face and plate edge attributes.



0007: Ctrl-Click Edit Nodes
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Moving nodes can be done with 2 simple clicks in Strand7 just like drag and drop.
  • Bring up the Edit/Nodes dialog box.
  • Holding down the CTRL key, click the node you wish to move with the left mouse button.
  • Now release the CTRL key and click the node you wish to move it to.
All Done! But don't forget to clean the mesh after you're finished.



0008: Right-Click Attributes
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Once you have applied an attribute to a particular element, you can easily apply a different type of attribute by right clicking over the existing attribute dialog box.

For example, you have just assigned restraints to a node and now you want to assign a force.

In the Node Restraints dialog box, right-click to bring up a list of attributes to choose from.

Select Force and you will find that the Node Force attribute is now the active dialog box. It's that easy.

This works for all attribute types in Strand7.


0009: Verification Manual
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Confused about how to set up your nonlinear model?

Example models can be found in the Strand7 Verification Manual.

You can find the "Verification Manual" folder within the main Strand7 program folder on your computer. Here you will find around 350 Strand7 models set up and ready to run.

The Verification Manual PDF contains the documentation that describes each model and compares Strand7 results with target values. There are examples for all of the solver options available in Strand7, divided into separate sections for easy identification. It's a great first reference for how to set up your model.

0010: Subdivide only Normal Beams
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When a model contains both normal beams and other line elements, e.g. trusses and springs, you may not want to subdivide the truss/spring elements when the beams are subdivided as it could lead to singularities.

Preferences within Strand7 can be changed so that when all beams in a model are selected, only those that are normal beams are subdivided. Choose Tools/Options. Under Subdivide set Subdivide only Normal Beams.


0011: Brick Cutting Plane Animations
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Viewing internal stresses in a brick can often be difficult and so the cutting plane option is used to view the stresses through a slice. You can then create an animation in the usual manner, (Results/Create Animation), which will create an animation of results for this slice.

But what about if you want to see this slice progress through the brick structure for a single load step?

Choose to create an animation and set Move Cutting Plane. When animated the slice will progress through the structure for that load step, between the extremities of the model.


0012: Auto-Assign Restraints
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When creating a rigid link array there is no need to go through the process of creating rigid links one at a time. Instead you can make use of the auto-assign tool in Strand7.

Select all the nodes you wish to be connected via rigid links then choose Tools/Auto Assign/Restraints. Select Rigid Connections as the Type and click Apply.

This will connect all the nodes via rigid links to an automatically generated master node, which will lie at the average of the selected nodes. Alternatively you can select your own master node for the rigid links to radiate from.

This tool is particularly useful for models that have bolted connections or areas where a point load is to be applied over an area.


0013: Ctrl-Click Retrieve
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Have you ever found yourself wanting to assign a restraint to a node similar to an adjacent node, or perhaps assign a common value of normal pressure to a brick face?

Within Strand7 is a simple procedure that can retrieve this information, ready for it to be assigned elsewhere. Open the required attribute dialog and then ctrl-click the node or element. The dialog will be automatically filled out with all the attribute values of the clicked entity, which can then be applied to other elements.

For example, open the node restraint dialog and ctrl-click a node with restraints. The node restraint dialog box will be updated to match the applied restraints. This procedure can be used for all element attributes.


0014: Run Time Improvements
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There are a few tips that you should keep in mind when trying to improve the run time of your Strand7 solve.

Firstly store your temporary files locally, not across a network. Choose File/Preferences, to change the location of your temp directory. Also if it is a very large model try saving the results files to your local drive while solving, reducing the time taken to write across the network.


However while all this will show some small performance improvements in solve time, for large improvements, the Sparse Solver should be top of the agenda.


0015: Strand7 Viewer
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If you have clients that don't have a copy of Strand7 and you want to be able to display your Strand7 model and results to them in their office the Strand7 Viewer can be used. You can download a free copy of the Strand7 Viewer from here.

This allows you to interrogate a model file and results in the same way as you would in the full version of Strand7.


0016: Edit-Delete-Attributes
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If you find the need to delete all attributes in a model without deleting the elements themselves there is a simple tool to do this.

Choose Edit/Delete and select Attributes Only. You can then choose whether to do so for all cases or simply a single case.


0017: Animations in Powerpoint
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When presenting your Strand7 analysis to your client a PowerPoint presentation can be very effective. To give depth to the content a Strand7 Animation of results can be included.

There are three methods that can be used:
  1. Save the animation as an AVI file. Then insert it into your slide.
  2. Save the animation as an EXE file. Then in PowerPoint choose to Insert a Hyperlink and browse to the correct location.
  3. In the Strand7 Animation Window choose to save the animation as a series of images. Then create a gif animation of these in an appropriate software package This can then be inserted in the PowerPoint presentation with the animation permanently running.


0018: Summary-Information
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At the top of every print from Strand7 a title block is presented where information on Project Title, Company Name, etc. can be given.

To fill this in simply choose Summary/Information and complete the required fields. The information here will then be displayed on all Print jobs from Strand7 (unless turned off).


0019: Length-Area-Volume Loads
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The ability to assign element attributes based on their geometry is a particularly useful one. In Strand7 attributes can be assigned based on the length of a beam or plate edge (L), the area of a plate or brick face (A) and the volume of a brick (V). For example, a beam pre-tension that is proportional to the beam's length can be applied by entering an equation such as 2.5*L, where L represents the length of each beam element.

Furthermore, each of these variables can be prefixed with the letter T, signifying Total, e.g. if five plate elements are selected, to assign a force of 1500N, enter 1500/TA which will divide the force by the total summed area of the five plates to give the correct pressure.


0020: Draw Ply Axes
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If your model contains laminate properties you may wish to investigate the local axis orientation of a specific ply.


Choose View/Entity Display and when you set Draw Axes for plate elements also enter the ply number you wish to view them for in the box on the right. Plate axes for that ply will be displayed on the element.

0021: Hide Zeros
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Have you ever found yourself with so many linear or nonlinear load case combinations that you lose track of which columns have load and which are set to zero?


In Strand7 there is a quick and easy way to hide all those zeros; to make viewing loads a breeze. In the Linear load case combinations (or nonlinear load increment) window, right-click and select Hide Zeros. All zeros are hidden making it a simple matter to see where all the load has been applied.

0022: Whiteboard
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Determining the distances between two nodes is an easy process in Strand7. Choose Summary/WHiteboard and click the two nodes you wish to determine the distance between. Information on the node numbers and attributes will be displayed. Along with this will be a straight line distance between the two nodes and relative distances, DX, DY and DZ.

If three nodes are selected then along with the distance between the nodes, an angle between the nodes will be given. Information on other elements can also be shown in the whiteboard, for example, plate area, brick volume etc.

0023: Nonlinear Convergence Graph
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Convergence of the nonlinear solvers is based on the displacement and force norms for the model for each iteration. Within R24 you can now click in the solver panel to display a graph of the displacement and force norms for each iteration.This means that it is easier to track the path of convergence of the model.

0024: View Load Factors
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With the release of Strand7 R24 comes the ability to view the applied loads for a specific load case combination, nonlinear load increment, quasi-static or transient dynamic time step. Results/View Load Factors will show the load factors applied for each load case for the displayed result case.

0025: Anchoring Node Coordinates
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If you wish to create nodes in a specific plane or line, you can anchor one or more nodal coordinates and then enter the remaining values.

In the Create/Node dialog enter the coordinates that are to stay the same, e.g Z = 250. Then clear the Z checkbox. Now every node that is created when an X and or Y coordinate is entered will be at Z = 250.

0026: Background Image
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A background image can be added to your Strand7 model window to allow you to include your company logo or perhaps a theme that matches your structure to "jazz up" the presentation of your model to your client.

Choose View/Options and select the jpeg or bmp image you wish to use as the background. This will be displayed in the model window. The model can still be manipulated within Strand7 as per usual.

0027: Numbered Backups
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You can set the file preferences to allow Strand7 to save your model with a different numbered backup every time you click save.

This should give users peace of mind, knowing that model changes can be retraced and, more importantly, recovered. This Option is accessed via File/Preferences.

0028: Select Brick or Plate Faces
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You can select brick or plate elements based upon the relative angles between free faces. This is useful for situations where a surface pressure needs to be applied, but the shape does not lend itself to easy selection using Select by Region or any other convenient method.

Command accessed via Select/Brick(or Plate) Faces.

0029: Plate and Brick User Contour
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For plate and brick elements a User Contour based on stress and strain result quantities can be defined in Results/Results Settings. This is useful in plotting the contours of derived quantities based on the elemental stress and/or strain, for example a material failure criterion. This quantity is also available for the Peek tool and in the Results Listings.
In this example, we derive and contour a concrete cracking index according to , where ft(t) is the tensile strength at age t obtained from concrete design codes and s1(t) is the maximum principal stress calculated by Strand7.

Since only the tensile stress is required, the function IFPOS can be used in this case, for example "IFPOS(x)" returns "x" when "x" is positive otherwise it returns "zero"). The user contour by the equation "0.35*SQRT(32)/IFPOS([S11])" indicates that some cracking can be expected in the concrete beam due to the creep and shrinkage where no pretensioning has been applied.


0030: Skip Transitioning
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Skip Transitioning is an automeshing option that aims to produce a mesh as regular as possible by ignoring small features in the geometry. This option can be used in conjunction with the Vertex/Mesh Size attributes to create a mesh with specific boundaries such that it can be directly "stitched" onto the existing mesh.
Initial Mesh:
A modification is required to include an additional hole to the existing mesh.
Using geometry tools such as Face from Beam Polygon and Graft Edges to Faces, a geometry face with a cavity can be created. Additional vertices with matching Mesh Size attributes are created.

Geometry tools are accessed via Tools/Geometry Tools.
Final Mesh:
The geometry face is surface meshed with the Skip Transitioning option and the mesh will be modified with the required feature.
Skip Transitioning can also be useful for skipping over small features, such as small mismatched edges producing small element edge lengths.


0031: Browse...
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If you are trying to find a model and cannot remember its name you can try using File/Browse in Strand7.

Navigate to a likely model location in the Browse window and click Browse. This will display an image of the last saved model view with the file name of all Strand7 files located in this folder. A little contour bar is displayed in the bottom left hand corner of the image if the model has results.

Also, if you right-click a model image you can open, rename, delete or see information about the file.


0032: Middle Button for Dynamic Rotate
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As of R242 you can now quickly switch to dynamic rotate mode by simply clicking the middle mouse button. The Equivalent keyboard shortcut is the F4 key.

Refer to the Online Help for other shortcuts.

0033: User Contour of Principal Stress with Largest Magnitude
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For plate and brick elements a User Contour based on stress and strain result quantities can be defined in Results Settings. This is useful for plotting contours of derived quantities based on the elemental stress and/or strain, such as a contour of principal stress with largest magnitude according to:

smax = MAX( s11, s22)

This allows you to display both maximum principal stresses in the same contour. Enter the following formula into the user defined contour for plates:

IFPOSB(ABS([S11])-ABS([S22]))*[S11]
+ IFNEGB([S11]-ABS([S22]))*[S22]

This produces the signed principal stress with largest magnitude.
IFPOSB(X) evaluates to +1.0 if X is positive and 0.0 if X is negative or zero.
IFNEGB(X) evaluates to +1.0 if X is negative and 0.0 if X is positive or zero.
To plot the absolute value of the principal stress with largest magnitude enter:

IFPOSB(ABS([S11])-ABS([S22]))*ABS([S11])
+ IFNEGB([S11]-ABS([S22]))*ABS([S22])

Substitute [S33] for [S22] when contouring for bricks.
The signed principal stress with largest magnitude for bricks is shown below.

0034: Perspective in 3D Drawing
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Strand7 allows you to change the perspective setting in a 3D model (View/Options/Drawing) so that you can see the 3D model on a plane view (say YZ plane view) more clearly. The setting is simply a number that ranges from 0 (no perspective) to 200 (very high perspective, like a fish-eye lens). It can be very useful when viewing/editing a complex 3D model.

Isometric view with Perspective set to 25 (default) YZ plane view with Perspective set to 25 (default) YZ plane view with Perspective set to 0 (parallel view)

0035: Beam Local and Principal Results
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Cross sections in beam elements contain both local and principal axes and they do not necessarily coincide (e.g. in the case of unsymmetrical or user defined sections).

For example, the principal axes of an equal angle section are oriented at a 45 degree angle from its local axes.
To help make the extraction of beam results more versatile, Strand7 reports beam forces and moments in both the local (x,y) and principal (1,2) axes.

For example, the highest bending moment at the root of the cantilever beam shown is reported in plane y if the load is applied in the Global Z direction.

0036: Selecting All Entities Behind the Selection Box
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One new feature in R245 is the ability to select both visible and obscured entities by using Ctrl+Alt when dragging a selection box. Instead of selecting only those entities which are visible from the current view point, all entities behind those shown are also selected. This alternative selection mode is graphically shown during selection on the screen as a solid double line.


0037: Geometry Creation in Strand7
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As an alternative to importing CAD geometry for automeshing, you can create geometry in Strand7. This is done by creating plate elements, and using Tools/Geometry Tools/Face from Plate to convert them into geometry faces.
Curved plates (i.e. Quad8, Quad9 and Tri6) can be used to create curved geometry faces. Set the option Circular Face Edges to create geometry faces on underlying cylindrical geometry. Otherwise, the quadratic shape of the original plate is retained for the geometry and the face becomes a b-spline.
This functionality can be used to patch holes in pre-existing geometry, or to build geometry to automesh in Strand7, independently of CAD software.
These faces can then be automeshed, or exported to CAD using File/Export and selecting IGES or STEP formats.
Note that it is also possible to convert planar polygons into faces by using Tools/Geometry Tools/Face from Beam Polygon.

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