Strand7 Software:  Release History:  Release 2.3

What's new in Strand7 Release 2.3

April 21, 2004

Strand7 2.3 will be released on May 3 with a host of new features and enhancements. The following is a summary of What's New in Release 2.3.

  New Import and Export Options
  New Link Type
  New Load and Freedom Case Options
  New Element Attribute
  New Tools
  New Material Options
  New Display Options
  New Table Options
  New Solver Sections
  New Results Options
  New Graphing Options
  New API Functions
  Functionality Changes
  Coming Soon

  1. Any models created in a previous release of Strand7 are fully compatible with Release 2.3. Models created or saved in Release 2.3 cannot be opened in any previous release. However a text export feature is available which is backwards compatible.
  2. Release 2.3 requires a new authorisation key.

New Import and Export Options
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The NASTRAN PLOAD attribute is now available when importing into Strand7.

Frameworks via IGES files
IGES files containing only lines (e.g. wireframes not surfaces or solids) can now be imported as beam elements.

Subfigure Iges Imports
Most solid modellers use the IGES Subfigure Instance Entity for defining solids; this is now supported by Strand7 when importing IGES files. Strand7 assigns each subfigure instance to a different group, ie each solid to a different group, thus making tet meshing easier.

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New Link Type
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Two Point Link
Users of Strand6 may remember a basic version of this link type, the two point constraint. This allows the user to create a link between two nodes coupling the degrees of freedom (DOF) by a linear equation, ie DY of Node 1 equals 2.5 times DZ of Node 2 plus a constant. The DOF can be defined in any UCS.

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New Load and Freedom Case Options
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Load and Freedom Case Dialog Updates
To help you with model verification, the Global Load and Freedom Cases dialog box has been changed. Now, primary load cases with zero gravity and acceleration values can be set to No Inertia instead of assigning 12 zero values.

New Inertia Relief Freedom Case
In the Global Load and Freedom Cases dialog box you now have the option to choose the type of each Freedom Case. In addition to the previously available normal freedom case, you can now select an inertia relief freedom case. Inertia relief freedom cases allow free-floating structures with static loads (such as marine or aeronautical) to be solved using the linear static solver, without applying any nodal restraints. We know that constant external forces applied to a free body will cause the body to move with constant acceleration. If the external forces do not change with time or the rate of change is small we can assume that the body inertia force is in equilibrium with the external forces. If the freedom case is an inertia relief case, then global linear and angular accelerations are automatically applied to generate inertia forces that balance the user-applied loads. Inertia relief freedom cases are available for completely free bodies and symmetric free bodies (such as where a half or a quarter of the structure has been modelled).

Equivalent Seismic Loads (Quasi-static earthquake analysis)
Most of the earthquake structural design codes (eg AS1170.4 and Eurocodes EC8) offer the possibility of simplifying the earthquake analysis of buildings by performing a quasi-static analysis in place of a full spectral or transient analysis, provided the building satisfies certain criteria. The quasi-static analysis involves distributing a certain portion of the total weight of the building as a series of horizontal loads that vary with height above ground level. The distribution and application of the horizontal loads can be fairly complex and time consuming if performed by hand. In Strand7 this load can now be applied automatically, simply by entering the required seismic coefficients to define any number of additional seismic (quasi-static) load cases. These seismic load cases are defined in the same way as primary load cases and therefore can co-exist with the primary load cases in the same linear static solution file (.LSA). This greatly simplifies the combination of primary and seismic load cases.

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New Element Attribute
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Beam Distributed Force and Moment
By selecting from a distribution pattern you can now apply constant, linear, triangular or trapezoidal distributed forces and moments to beam elements. You can choose to assign up to 64 sets of distributed loads on a single beam in one load case.

Beam Point Forces and Moments
You can choose to assign up to 64 point forces and moments on a single beam in one load case.

New String Group
Connected truss elements can now be grouped together to form a string group. The string group acts like a string passing through a series of frictionless pulleys. A pulley is located at every node and as they are frictionless a constant tension is recovered in all the truss elements of a string group. A string group can be an open-ended one or a closed loop.

This attribute allows very complex nonlinear loading sequences to be applied. The following figures illustrates a simple example: one end of a string (shown in red) is connected to a 2D frame structure and made to pass through a series of virtual pulleys. The other end of the string is pulled downwards via a prescribed restraint. The progressive response (absolute scale of 1) of the structure is shown in the multi-view display.

Cable Element Subdivision
Catenary cable elements can now be subdivided. Users will find this useful for applying point loads part way along a complete cable section.

Pipe Pressures/Temperatures
Internal and external pressures are now assigned in the same attribute dialog box, as are internal and external pipe temperatures.

New Load Patches
This is one of the major new features in this release. The Load Patch is a new type of plate element that has no property attributes and is used solely for transferring loads distributed over an area to beams connected around the perimeter of the load patch. An example of this would be transferring wind loads to the side of a building or live loads on a floor slab. The load patch converts the area load into an equivalent line load on the beam. Plates can be assigned as Load Patch type in the Plate Property Dialog box. This greatly simplifies the application of loads to a complex array of beams; simply changing the load on a single plate automatically changes the load on the perimeter beams.

Consider the following example. Both models are a frame of beam elements. In the model on the left the load is applied via a subdivided mesh of membrane elements and corresponding beam elements; in the model on the right the load is applied using a single load patch with a single beam element along the load patch edge. You can see that the bending moment diagrams for both cases concur well, yet the load patch model is significantly easier to construct and to post-process.

The Load Patch attribute is applicable only to plates which have been assigned the Load Patch property. This attribute dialog box presents a range of 6 different load distributions to choose from for transferring the loads to the underlying beams.

For all except the user-defined distribution, the total load applied to the surrounding beams is equal to the total load applied to the load patch, assuming there are beams along the appropriate edges of the load patch. If there is no beam present that load portion is lost. For this load transfer to occur, beams do not necessarily need to span the full edge of the plate but can in fact be longer, shorter or there can be multiple beams along the edge.

Loads can be applied to the Load Patch elements as Plate Normal Pressure, Plate Global Pressure (projected and not projected), Plate Face Shear and Plate Non-Structural Mass. The first three are converted to beam global distributed forces, the fourth is converted to beam non-structural mass.

There are two additional features relating to Load Patch that will be useful:

Firstly, Strand7 2.3 is equipped with a Create Load Patches tool. This tool provides an automatic way of defining load patches over any flat polygon of beam elements. Simply select the beams required, be they in 2D or a 3D framework, and where appropriate the tool will create Load Patch plates. The following figures gives some examples of this.

The second tool is the Convert Patch Loads to Beam Loads. While this is not actually required for the analysis as the loads on the patch are always automatically converted for the solver at commencement of the solution, it can be a useful for viewing the load distribution on the beams that Strand7 has automatically determined. One important point to note however, is that once the patch loads are converted to beam loads, either the patch loads or the beam loads should be deleted before running the solver, otherwise double the load will be applied.

Plate Thickness
Strand7 2.3 allows plate thickness to be applied directly to plate elements as element attributes, independently of the thickness assigned in the element's property set. This is useful if local changes in thickness occur and eliminates the need for multiple properties if only the thickness differs. Both membrane and bending thickness can be assigned in this way.

Plate and Brick Global Projected Pressures
Previously in Strand7 when projected global pressures were applied to plates or brick faces, the projection was of the resultant pressure load onto a plane perpendicular to the direction of the resultant pressure vector. Now you can choose to project the pressure as a resultant load (as previously) or as three independent components.

The following figure illustrates the difference.
The model contains two plates at an angle of 45 degrees, each with a global face pressure of X = 1 and Y = 1. The plate on the left has the pressure applied as projected resultant. This means that the load is acting along the plate, therefore the projected area in this direction is zero and hence no pressure is applied (thus no reactions occur at the restraints). However the plate on the right has the pressure applied as projected components. This means that the pressure loads acting on the plate are calculated based on the vertical and horizontal projected areas, independently. Therefore in this case there are reactions occuring at the restraints. The important point which differentiates the two approaches is that the projected area of the plate relative to the component and resultant pressures are different.

Brick Local Axes
Brick elements can now be assigned a UCS to define a local system. This will be very useful for both results extraction and for orthotropic material definition. Previously in models like this we needed to divide the model into different property sectors and define material axes for each property. This is now redundant as we can assign a UCS to the bricks. Strand7 will then determine an orthogonal set of axes formed by the UCS for each Gauss point of each brick.

You can also display brick local axes in the same way that you can display plate local axes.

Brick Pre Stress
Brick elements can now be assigned a pre-stress.

Non-Structural Mass
This is the other major new feature of release 2.3. As the name suggests, it is a mass that is not part of the structure. This attribute is mainly used for modelling live and non-structural dead loads which may vary across a range of operating conditions. For example, furniture not fixed to a building will generate gravity loads on a building slab and therefore can be modelled as a non-structural mass. Previously this has been modelled as a pressure, however in dynamic analysis a pressure has no effect on the inertia of the structure.

The non-structural mass attribute is load case specific and within the Load and Freedom Case dialog box you can choose whether to include/exclude structural mass and/or non-structural mass for each load case. This has the added benefit of allowing the user to include the structural mass of the structure only in the self weight load case, ensuring that the self weight effect is included correctly and only in one load case.

Four types of non-structural mass attributes are available for node, beam, plate and brick elements. Their application is as follows:

Node - A single value applied as a concentrated mass in the three translational components.

Beam - Applied as a mass per unit length. In this case the density may be constant over the beam or applied as a varying distribution over the length of the beam, in the same fashion as the beam distributed force.

Plate - Applied as a constant mass per unit area.

Brick - Applied as a constant mass per unit area to any face.

Each of the four attributes also provides the option to apply a dynamic factor. For a static analysis the non-structural mass attributes will generate gravity loads when non-zero global accelerations are applied. When no global accelerations are applied they will have no effect on the analysis results. In dynamic analysis, the magnitude of the non-structural mass is multiplied by the dynamic factor to obtain an effective mass to be added to the structure's mass matrix.

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New Tools
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Mid-Plane Extraction
This tool can be used to obtain the mid-plane between two plates, as shown in the following figure. In this case the red plates are a mid-plane projection of the blue and green plates.

New Subdivide Tool Option
The Tools Option dialog now provides the option to choose the method of aligning plate axes after subdivision. There are two different methods of alignment, parent centroid and curvilinear.

For parent centroid, the local axes of the new subdivided plate elements will be parallel to the parent plate element.

For curvilinear, the local x-axis of the new subdivided plate elements will be aligned with the first curvilinear axis (natural coordinate system) of the parent element.

Group Solid Automeshing
Under the Options tab of the Solid Automeshing dialog there is now the Groups as solids option. If set, then during a tet meshing operation the selected plate elements are meshed separately according to their group.

Take the example below. The gear contains 3 separate solid bodies that we wish to mesh. Each of these solids has been assigned to a separate group, automatically during the CAD import phase.

Using the Groups as solids option we can mesh all the solids at once, producing separate properties for each group. Without this option we need to select each group independently and mesh it before moving on to the next one.

Beam Frameworks
A tool now exists that allows you to align a framework of beams according to the surface that defines this framework. You have the option to align the 1, 2, local x or local y axis with the surface normal.

Take the following example. Below is a free form surface of beam elements.

The first figure below, shows the framework with beams aligned inconsistently (ie using the default beam axis system orientation). By using the align beam framework tool we can align the beams in a consistent manner as per the second figure below.

Element Subdivide Options
Right-clicking on the subdivide dialog creates a pop-up of options for the subdivision. You can choose to swap the subdivision axes, or automatically fill in common subdivision numbers.

Improved Smooth Plate Tool
The tool now offers the option to smooth or not smooth the edge nodes. In addition, the quality of smoothed mesh will in general be better than previous releases.

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New Material Options
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Composite Material Library
The ability to create a material library (including allowable limits) for composite plies is now available to complement the general purpose material libraries and the beam section libraries. Once created you will be able to select a ply from the library option in the Ply Property dialog box.

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New Display Options
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Beam Distributed Forces Display
Beam distributed forces can now be displayed as either vectors or lines. The lines option will make it easier to visualise triangular and trapezoidal load distributions on beams.

Link Free Ends
Now like beam free ends you can now choose to display link free ends. Also within View Options you can define what constitutes a link free end, ie when it is connected to plates, bricks or beams.

Vertex Attributes
You can now choose to display vertex mesh size attributes on your Strand7 model using the Attribute Display Dialog.

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New Table Options
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Auto Generate Stress-Strain Curves
The equation editor in Strand7's Stress vs Strain Table now has a new feature, an automatic Elasto-Plastic Stress-Strain Curve. By entering three parameters, E0, yield stress and Et (the post-yield tangent modulus), Strand7 will generate a simple stress vs strain table.

Convert Time Response to Spectral Response
Within Strand7 it is now possible to convert an Acceleration vs Time table into an acceleration response spectrum. Users will find this useful when they wish to run a simpler spectral solution instead of the potentially longer transient solves.

The following figures give an example of this function. The first figure is an Acceleration vs Time table, while the second figure is the corresponding Acceleration Response Spectrum.

Alphabetical Table Names
Selecting a table from a list has now been made easier with table names stored in alphabetical order. This means that modifying a table will not send this table to the bottom of the list. This is also the case for laminate names in the laminate property dialog.

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New Solver Options
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Harmonic Solver Option
The harmonic solver now gives the user two results type options: you can choose to solve vs frequency or vs time. Previous versions of Strand7 have provided only the option to solve vs frequency but now when the load type is Applied Load you can choose your results type to be vs time. Choosing the vs time option will disable the range option on the harmonic solver dialog box.

Instead, when you click the load cases button you can enter a load factor, phase and frequency at which that load case acts. This means that different load cases can act at different frequencies, but all are applied to the structure simultaneously.

When post processing the results you can choose from two different modes in which to view them: you can view the maximum contribution of each individual load case or you can now select Harmonic Time history.

Harmonic Time history will produce results that can be viewed as a time history of all the loads acting together at their respective frequencies and phases. The number of time steps, the total time and the size of the steps is determined by user input when the option is selected.

Warning and Error Summary
A summary of the total number of warning and error messages generated during the solve is now given at the end of any solver log file.

Hide Zeros
It is now easier to verify the load increments used in the nonlinear static solver by hiding the zero values. Right clicking the load increment dialog and selecting Hide Zeros will display only the non zero values in the load increments. This option is also available for Linear Load Case Combinations.

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New Results Options
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New Envelope Type
Changes have been made to the envelope function within Strand7 to incorporate new envelope types in 2.3. Three types of envelopes are now available: limit, combination and factors.

The function of limit and combination envelopes remain as they were in Strand7 2.2.x, the new envelope type is the factors envelope. This envelope allows multiplication factors to be applied to the included result cases. It further allows Additive/Exclusive operations to be applied to sets of result cases. The factors envelope accumulates values for the included result cases according to these inclusion options and multiplication factors. They can be either maximum or minimum.

The name and type of the factors envelope is defined in the left hand section of the dialog box. The contents of the envelope is defined in the right hand side of the dialog box.

The user selects which results cases are to be included (a single result case can be included multiple times). A pair of factors is entered. Both factors are considered in turn but only the factor that leads to the greatest increase in the magnitude of the envelope total is used, depending on whether a minimum or maximum type has been selected.

You can also group result cases together into sets to allow additive/exclusive operations in the "set" subtotals. This is done by using the Sets option in the factors envelope dialog and assigning them to result cases.

Set types can be either Exclusive (OR) or Additive (AND).
  • Exclusive (OR) defines a set of result cases from which only the result from a single case is included in the envelope. This is the case that leads to the largest increase in the total envelope.
  • Additive (AND) defines a set of result cases for which all of the result cases are considered in addition. In other words each included result case in the set is added, based on the factors applied, to a final Set value.
The Additive set is used in conjunction with the groups attribute, which can be assigned to sets. The group attribute allows several sets to be grouped and can be thought of as a set of sets. Groups are always exclusive and hence only the greatest result of the group is added.

Expanded Results for Envelopes
It is clear that envelopes are very powerful for providing extreme results values for use in design calculations. For example you can determine the extreme displacements that occur for one node in a model. However, if more than one load case has been considered in determining the maximum for that node it is unlikely that the values for all maximum displacements are caused by the same combination of load cases. That is it is not likely that the maximum DX is occuring as a result of the same load combination that is causing a maximum DY.

For design purposes, it is often necessary to know the full set of values in equilibrium when a particular maximum result occurs. In other words, what are the equilibrium values for DY, DZ, RX, RY and RZ when DX is maximum. This can now be found in Strand7 by selecting the Expanded option when viewing envelope results. This will generate a matrix of results with each row being a set of equilibrated results. The Expanded values can be viewed in both the peek tool and the results listing by selecting the Expanded button or selecting Envelope:Expanded respectively.

Envelope Case Positive or Negative
The option to show envelope cases as positive or negative has been removed as the value shown is now controlled by the type of envelope selected, ie Max, Min or Absolute. Beam diagrams continue to show both Min and Max values simulataneously for the limit envelope cases.

Brick Local Axes Contours
With the addition of the ability to assign brick local axes, you can now choose contour brick results for local axes as well as global, UCS and combined.

Brick Cutting Plane
A new option exists when selecting to contour brick results on a cutting plane, About Centroid. If this is set then the moment integrations are performed about the centroid of the section cut by the cutting plane.

Floating Contour Legends
When using the floating contour legend it will now keep the same position when printing or exporting an image.

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New Graphing Options
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Strand7 2.3 offers the option to convert a transient response represented in the time domain into a result represented in the frequency domain, via Fast Fourier Transforms (FFT). Representation of time history results in the frequency domain is useful because it allows easy identification of the frequency content of the results.

The FFT tool comes with a number of options.
  • Filter Window - This option allows the selection of the technique to be used to filter the raw data.
  • FFT Output - This chooses which results to display after conversion. If the FFT generates a complex number, a + ib at each time step, then you can choose to display either the real part, imaginary part, magnitude, phase or power spectral density of the result.
  • Interpolation - The algorithm used to do an FFT transform requires two important features: firstly the number of points to be transformed must be a power of two and secondly the spacing in the time domain must be constant. In Strand7 these limitations don't exist so we need to fit a polynomial curve to resample the data appropriately.

The following figures show this function in operation. The first figure shows a time response while the second figure is a frequency response. The frequency content of the results can be clearly seen in the response vs frequency plot: in this case, a significant component at zero Hz and another at around 47 Hz.

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New API Functions
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API functions
The Strand7 API, released in Strand7 2.2.x, has been very well received by users and already there are a number of applications and special-purpose tools developed by Strand7 users. In Strand7 2.3, over 100 new functions have been added to the API set including functions for:

  • managing non-linear load increments;
  • managing restart files;
  • extracting other result types;
  • assigning the new attribute types available in this new release.
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Functionality Changes
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More Sophisticated Parsing
In Strand7 it has always been very easy to assign attributes via the definition of equations. For example, a pressure distribution around a circular object, like a silo, can be applied by simply entering the equation of pressure as a function of angular position and/or height around the silo; Strand7 will evaluate the function at each element and apply the correct value of pressure automatically. In Strand7 2.3, the functionality of the equation parser has been expanded; it now supports variables representing length, area and volume of the element, in addition to the previously available spatial coordinates. 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. Similarly the variable A can be used to represent the area of a plate or the area of a brick face and V can be used to represent the volume of a beam, a plate or a brick. Furthermore, each of these new variables can be prefixed by the letter T, signifying Total. For example, if more than one plate element is selected, assigning a total force of 1.5 to them via a pressure distributed over all the selected plates, can be achieved via the equation 1.5/TA: firstly the sum of the area of each plate is calculated and assigned to the variable TA; secondly the pressure assigned to each plate is calculated as 1.5 divided by the sum of the area of all the selected plates.

Font Changes
One of the first things you will notice about Strand7 2.3 is that it has undergone a font change. The standard font now used throughout Strand7 is Tahoma. This change was necessary for better representation of Strand7 screens and dialogs in languages such as Japanese and Chinese, which are supported by Strand7.

New Hot Keys
One of the simple yet extremely useful functions in Strand7 is the addition of new hot keys. The selection arrow can now be toggled between on and off by simply hitting the spacebar instead of using Ctrl-Space. Also implemented in this version is the ability to toggle on and off entity selection. For example hitting the N key on the keyboard will toggle node selection on and off. Similarly you can use B for beam, P for plate, K for brick, L for link, V for vertex, G for geometry, X for Additive/Exclusive, D for all down and U for all up.

Online Editor Group Path
Right-clicking in the online editor now includes the option to Show Group Path. Selecting this will configure the groups column to display the full group name. With this unchecked only the final string will be displayed.

Preferences for Opening Results
File/Preferences/Results is a new menu in Strand7 that allows the user to choose how load case combinations and envelopes are handled on opening and closing.
For example for Load Load Case Combinations you can choose to:
  • Always generate: When results are opened any defined linear load case combinations will automatically be generated.
  • Never Generate: When results are opened any defined linear load case combinations will not be generated.
  • Prompt: When results are opened a dialog box will appear asking if you would like to open any defined linear load case combinations.

Print Results File Name
In print setting you can now choose to display the result file name at the bottom of the page in addition to such things as the model name and date and time.

Online Help
The comprehensive Strand7 Online Help has been updated to feature a new window layout that has the global navigation controls in a navigation pane to the left of the content pane. The toolbar pane at the top of the window contains buttons that will be familiar to anyone who has used WinHelp before.

Show Models in Taskbar
The Other tab in the Strand7 Preferences now gives the option to Show model windows in the task bar. If set, each model has its own entry in the Windows Taskbar making it easy to switch between models.

DDE Multi-Launch
Provided Strand7 is properly installed, when an ST7 file is double clicked in Windows Explorer (or on the Desktop), Strand7 is automatically launched and the ST7 file is opened in that Strand7 session. If Strand7 is already running and another ST7 file is double-clicked, in previous versions another copy of Strand7 was launched. In 2.3, if Strand7 is already running, that instance of Strand7 will detect that a new ST7 file is to be opened and instead of starting a new copy of Strand7, the new file will be opened in the existing Strand7 session. This will help conserve resources when multiple ST7 files are to be opened simultaneously.

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Coming Soon
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Theoretical Manual
Shortly to be released is the Strand7 Theoretical Manual. This manual aims to answer some of those sticky questions users have on the theory behind the Strand7 FEA system. For example, how are point contact elements formulated or what is the theory behind the Mohr-Coulomb failure criteria. Stay tuned for more details.

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