Strand7 Pty Ltd

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News.St7 Newsletter for Strand7 and Straus7 users

Strand7 is marketed as Straus7 in continental Europe

Welcome to another issue of News.St7 for 2005. In this issue we would like to say a special hello to our Strand7 users in the United Kingdom who may be reading this for the first time, and to those who are regular subscribers. This issue of News.St7 may be of particular interest to those of you in the UK as we feature the launch of Strand7 UK Ltd, an office of Strand7 dedicated to our users across the ocean.

Of course this issue is also of interest to all Strand7 users as we feature articles on how Strand7 is being used for a wide range of applications from analysing bat skulls to looking at the stresses in a reinforced tunnel.

We also feature articles on plate axes alignment, identifying ill-conditioning and the usual array of Did You Know items to motivate the mind. If you have any feedback or suggestions regarding the content of News.St7 or would like to feature any of your projects then please email news.st7@strand7.com. If you would like to automatically receive your copy of News.St7 directly by email simply send a blank email to newsletter-subscribe@strand7.com. All care is taken to ensure that information in News.St7 is accurate and up to date at the time of publishing. However Strand7 Pty Ltd accepts no responsibility for inaccuracies in, or changes to, such information.

Earlier this year the office of Strand7 UK Limited opened

its doors; the first office of Strand7 Pty Ltd to be located outside of Australia. This office is seen as an investment into expanding the already healthy relationship that exists between the developers of Strand7 and UK users.

Located in the bustling town of St Neots, the third largest town in Cambridgeshire, and just 57 miles from London, Strand7 UK has become the centre of all contact for users across Great Britain. Whether it is just information you require, or more detailed Strand7 support, this office is the first port of call for all users, and potential users, in the UK.

Having a direct presence in the UK will give Strand7 users significantly enhanced technical support and a more direct link to the Strand7 Software development team back here in Australia.

The number of Strand7 users in the UK has grown consistently in recent years and Strand7 is now widely used in a range of engineering disciplines including mechanical, aeronautical and automotive applications.

Figure 1.1 - Location map of Strand7 UK Limited.

In addition, Strand7 is increasingly being used for civil/structural applications by UK consultancies looking to perform more sophisticated analysis than what is usually possible with traditional frame analysis software.

In the upcoming months the links between Strand7 UK and Strand7 Pty Ltd will become more and more apparent, with many joint activities planned for the

In this issue…

• Feature Article 1

• Strand7 Skull Analysis 2

• Plate Alignment 4

• Identifying Ill-Conditioning 7

• API in the Field 9

• User Jobs 10

• Training 12

• Exhibitions 12

• User Profile 12

Issue 5, September 2005

Strand7 UK Launches

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second half of the year. This constant contact will further enable our developers in Australia to create and expand features in Strand7 requested by customers.

November is the biggest month with visits, exhibitions and courses planned across the UK.

From November 22-24, Strand7 will have a booth located at Civils 2005, the UK’s number one civil engineering showcase. Civils 2005 is being held in the National Hall, Olympia, London.

Also in November we plan to hold a five day Strand7 training course in the UK. This course will follow the format of the recent external courses held in Melbourne and Brisbane, Australia, with a modularised course over the five days. Three days will be devoted to Strand7 Essentials and two days to nonlinear and dynamic analysis, subject to feedback from interested parties. For more information or to download the registration form go to www.strand7.com/training.htm. This course will be presented by Strand7 staff from Australia together with Strand7 UK staff.

If you would like any more information on Strand7 UK then please contact us at

Strand7 UK Limited The Studio Office Church Walk St Neots PE19 1JH England Tel: +44 (0) 1480 211 011 Fax: +44 (0) 1480 211 020 Email: info@strand7.co.uk Web: www.strand7.co.uk

We are always very pleased to hear from Strand7 users

Using Strand7 to Study the Mechanics of Feeding in Mammals

The earliest mammals were tiny, insect-eating creatures.

From these unremarkable ancestors, the diversification of mammals is largely a story about exploiting an ever broader array of food resources. Broad associations between the shape of mammals’ skulls and their diets are obvious. For example, the architecture of a cow’s skull enables it to chew grass efficiently while the skulls of tigers are well equipped to bite and tear flesh. Despite these correlations, we don’t understand the mechanistic link between diet and skull shape.

The skulls of mammals serve a number of different functions; protecting the brain, housing important sensory organs, and contributing to the first portion of the digestive system. Our lab investigates the hypothesis that skull shape has evolved (at least in part) to withstand the forces that are generated during feeding. We accomplish this by using data on feeding behavior and bite force

gathered from wild animals to load finite element models of mammal skulls. By varying the loading conditions, we study how skulls dissipate forces generated by typical and atypical feeding behaviors. We predict that forces are dissipated more efficiently via internal stresses in the skull (i.e., skulls are more resistant to feeding loads) under typical loading condition.

Bats are an ideal model organism for this work for three reasons. First, bats exhibit the greatest diversity in skull shape and broadest range of diet among all the orders of mammals. This allows us to compare animals that are closely related but have very different craniofacial structures. Second, the skulls of bats are more likely to be optimized to transmit biting forces than are those of other mammals because the metabolic cost of flight is high. Thus, any tendencies for the skull to be “overbuilt” should have been reduced over evolutionary time. Third, bats are among the most abundant mammals in the world and are relatively easy to work with in the wild.

Building a 3-D finite element model of a structure as complicated as a skull poses a significant technical problem. Because the skulls of the bats we study are roughly only 15-20mm long, we turned to micro-ct scanning to capture detailed anatomical structures (Fig 2.1). We built detailed surface models of entire skulls from stacks of serial ct-scans using AMIRA (Mercury Computer Systems) (Fig 2.2). The surface models were saved in STL format and imported into Geomagic (Raindrop, Inc.) where small, particularly complex regions of the skull were edited manually. Once we were satisfied with the geometry, we imported the models to Strand7 as a 3-D surface triangulation (i.e., an *.stl file). Within Strand7 a plate element mesh was automatically constructed from the imported *.stl triangulation.

Fig 2.1 – A single slice through the skull of a bat as seen in a micro-ct

scan. Bone is white.

Strand7 Skull Analysis

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Fig 2.2 – 3D surface model of the skull of the Jamaican fruit-eating bat

(Artibeus jamaicensis).

It is impossible to build such complicated models without errors and Stand7’s mesh checking algorithm has proven exceptionally useful. Nevertheless, there are inevitably many plate free edges and t-junctions that must be fixed manually. Once the plate models were free of errors, we used Strand7’s automatic tetrahedral mesher to create a volumetric mesh of ten-noded tetrahedrals. After this step, all plate elements were removed, leaving only a volumetric mesh that recreated the geometric structure of the skull in exquisite detail (Fig 2.3).

Fig 2.3 – FE model of the skull containing 251,968 tetrahedral elements.

Applying realistic loads to the models was, of course, crucial to generating meaningful results (Fig 2.4). We applied load vectors to three nodes representing each of the two primary jaw closing muscles: masseter and temporalis. Constraints were applied at the three places where the lower jaw contacts and transfers forces to the skull during feeding; the center of each jaw joint, and the tip of the tooth where biting occurs. A single node in the center of each joint was constrained against displacement. This effectively created an axis of rotation for the skull due to the application of muscle forces. To prevent this rigid body motion and induce elastic deformation in the skull due to biting forces, nodes on the tips of the teeth involved in biting were constrained against displacement

(i.e., displacements in the X, Y, and Z planes were set equal to zero).

Fig 2.4 – Point loads representing muscle forces (arrows) and constraints

(asterisks) at the biting tooth and jaw joints.

Each analysis of a biting behavior was completed in two steps. Initially, an arbitrary total amount of muscle force, FT, was divided between the masseter and temporalis muscles based on muscle mass proportions. All muscles were assumed to act simultaneously and all dynamic or transient effects were neglected. Once the analysis problem was solved, the reaction forces at the constrained tooth required for system static equilibrium were determined. This reaction force, n

RF , was then compared to experimental in vivo bite force measured for the bat species, Fexp. Since the computed reaction force is in direct proportion to the total applied muscle load, the required total amount of muscle force, (FT)new , necessary to yield the experimentally measured bite force is given simply by:

( ) TnR

newT FF

FF

= exp

In the second step of the analysis, the computed total amount of muscle force (FT )new, was distributed among the masseter and temporalis muscles based on muscle mass portions. The solution of this second analysis problem yielded the deformation of the bat skull, strains, and stresses for a particular feeding behavior that resulted in reaction force(s) at the constrained tooth (teeth) that identically matched voluntary bite force values collected in the field. Essentially, known bite force values were used to calculate the muscle forces required to maintain static equilibrium.

Perhaps not surprisingly, there is no data summarizing Young’s modulus or Poisson’s ratio for the very thin and highly curved bones of bat skulls. However, comparative studies of the stiffness and yield strength of cortical bone suggest that material properties are relatively constant over a wide range of vertebrates. Based on these comparative data, we assigned our models average values of Young’s modulus (E = 2 x 1010 Pa) and Poisson’s ratio (ν = 0.3) for cortical bone.

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Feeding behaviour experiments carried out in the field demonstrate that the Jamaican fruit bat typically bites hard fruits with the molar teeth on one side of its mouth; it rarely bites hard fruits with its canines. We found significant differences in the patterns of stress under these two loading conditions, especially in the palate (the roof of the mouth). During unilateral molar loading, stresses in the palate were relatively low and localized (Fig 2.5). In contrast, bilateral canine loading resulted in widely distributed stresses that were high and concentrated near the pterygoid plates (toward the back of the palate) (Fig 2.6).

Fig 2.5 – von Mises stress in the palate under the common biting

behavior (bite force = 22.5 N).

Fig 2.6 – von Mises stress in the palate under /atypical/ biting behavior

(bite force = 18.8 N).

The ease of extracting quantitative data from Strand7 also allowed us to demonstrate dramatic differences in the volume of the skull experiencing stress under the two loading conditions. After removing the elements affected by the application of point loads, a constant bite force led to a much larger proportion of the skull experiencing high stress under atypical loading compared to the common loading regime (Fig 2.7 and Fig 2.8).

Fig. 2.7 – Plot of stress versus skull volume demonstrates that the skull is

most resistant to loads imposed by the most common biting behavior.

Fig. 2.8 – Plot of stress versus skull volume for Atypical biting behaviour.

The bat skull does not constitute a “fully stressed design”. Rather, these data support the idea that the skulls of mammals are not optimized solely for feeding but represent a compromise between competing functional demands. Nevertheless, these results demonstrate a clear link between the loading regimes that routinely occur during feeding and the structure of the skull. Based on simple lever mechanics, bite force is expected to increase as bite points move closer to the jaw joints. However, the Jamaican fruit bat exhibits a greater than expected difference in strength between canine and molar biting. We hypothesize that the shape of this bat’s skull is a result of natural selection favoring an ever-increasing ability to apply high bite forces. This led to the shortening of the face, focusing biting behaviors on the molar teeth, and strengthening the skull to withstand unilateral molar loads

Article prepared for Strand7 Pty Ltd by Elizabeth Dumont, University of Massachusetts. Research is from the labs of Elizabeth Dumont (Biology) and Ian Grosse (Engineering) at the University of Massachusetts, Amherst USA

Plate Axes

Following on from our feature on Plate Orientation in

Issue 4 of News.st7 we discuss the concept of Plate Axes in Strand7.

Plate Alignment: Part 2

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Like plate orientation, plate axes form an important part of the quality assurance procedures of finite element modelling. This article discusses the impact that misaligned plate axes can have on results and also ways to identify and correct this.

Overview Plate axes refers to the plate local coordinate system. Every plate element has a local coordinate system with the x and y axes lying in the plane of the plate.

Fig 3.1 – Plate axes diagram for a Quad4.

Fig 3.2 – Plate axes diagram for a Tri3.

Figures 3.1 and 3.2 show the plate local x and y axes.

Plate Axes Convention? Plate axes are initially defined by the node connection order of each element. The default local axis system is defined as follows:

1. Positive local x runs from the mid-side of side N1-N4 to the mid-side of side N2-N3 for a Quad or from N1 to the mid-side of side N2-N3 for a Tri.

2. Positive local y is normal to the local x axis, directed away from side N1-N2 in the plane of the element.

Implicit in this definition of the local axes is the direction of a local z axis, which form a right-hand local coordinate system on the plate.

Viewing Plate Axes There is a display option in Strand7 that allows for the easy identification of plate axes in a model. Choose

View/Entity Display and click the Plate tab . Set Draw Axes. The local plate axes will then be drawn for each individual plate.

Fig 3.3 – Display of plate axes.

For clarity, this display option does not show the local z axis. However, the local z axis can be visualised by using the Orientation plate display option as described in Issue 4 of News.St7.

Why is this important? There are three main reasons why consistent and known local plate axes is important.

1. Some plate element attributes are applied based on the local coordinate system, including prestress, face shear stress and normal pressure. If plate axes are not aligned in a model then applied loads may be incorrect.

2. Local plate axes are used for non-isotropic materials, e.g. orthotropic or laminate materials. The 1, 2 and 3 directions for material properties, e.g. E1, E2 and E3 for orthotropic plates, refer to the material properties in the local x, y and z axes respectively. Note: For laminate properties you can also choose to display the plate axes for a specific ply, see the did you know on this page.

3. Plate force, moment, stress and strain results can be extracted based on the local coordinate system. It is important that plate axes are aligned when doing this to ensure that results are consistent. For plate/shell models, the local z axis is particularly important when looking at surface stresses and strains.

Did you know?

Draw Ply Axes 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.

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How can the Plate Axes be Changed? Two tools exist that allow the user to change the alignment of the x-y axes on plates. One is more commonly used to change the alignment of plate axes on an individual level while the other is very useful in a global sense.

Method 1 – Local Axis Angle.

• Choose Attributes/Plate/Local Axis Angle. Select the plates whose local axes you wish to change, enter a value for the angle and click Apply.

Fig 3.4 – Local Axis Angle attribute.

The local axis angle will re-orient the local axis system based on the default coordinate system. A positive angle rotates the local x axis in the right hand positive direction about the local z axis. To increment or decrement the current orientation angle, use the Add button instead of Apply.

Method 2 – Plate Axes • Choose Tools/Align/Plate Axes. Select the plate

elements you wish to align, choose the coordinate system and axis to align to, the local axis to align, and click Apply.

Fig 3.5 – Align Plate Axes tool.

Fig 3.6 shows the model in Fig 3.5 with the local x axis of the plate elements aligned with the positive global X axis.

Fig 3.6 – Aligned plate axes model.

What Happens When You Subdivide? There are two options available for plate axes when you choose to subdivide an element in Strand7, these are Parent centroid and Curvilinear. The option required can be selected by choosing Tools/Options and selecting one of the radio buttons under Plate axes alignment.

Fig 3.7 – Tools/Options Plate Axes alignment dialog.

The difference between the two options becomes more apparent when an element is highly curved as shown in Fig 3.8.

Fig 3.8 – Single Curved Quad8 element with local axis shown.

If Parent centroid is selected then all subdivided elements inherit the local axes alignment of the parent and therefore all resulting elements will have their local system parallel to each other, see Fig 3.9.

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Fig 3.9 - Subdivided Quad8 element with Parent centroid plate axes

alignment definition.

If Curvilinear is selected the local x-axis of all subdivided elements is aligned with the first curvilinear axis of the natural coordinate system on the element. For a curved (quadratic) element, this results in a series of local axes (non-parallel) curving around the element, see Fig 3.10.

Fig 3.10 – Subdivided Quad8 element with Curvilinear plate axes

alignment definition.

Conclusion The alignment of plate axes in a model should not be overlooked, especially if attributes, material properties or results that are based on local plate axes are used. Checking the alignment of plate local axes should form one of the items on a QA check list

What is Ill Conditioning?

Ill conditioning in Strand7 refers to an undesirable state

of the stiffness (or mass) matrix.

The matrix is considered to be ill conditioned if small changes in the coefficients of the matrix have large effects on the results.

A Numerical Example Consider the following simple set of equations:

−=

−

−000.2000.4

002.1000.1000.1000.1

yx

The solution is:

10001004

==yx

Now lets alter one coefficient of the second equation slightly:

−

=

−

−000.2000.4

001.1000.1000.1000.1

yx

The solution is now:

20002004

==yx

A 0.1% change in one coefficient has caused a 100% change in the solution!

A Mathematical Representation The first set of equations represents two straight lines in xy space:

000.2002.1000.1000.4000.1000.1

−=+−=−yxyx

The solution of these equations yields the intersection point of the straight lines. If plotted, these two lines are nearly parallel. Changing the coefficient from 1.002 to 1.001 in the second equation, represents rotating the second line slightly, but doing so changes the intersection point significantly.

A Structural Representation The two connected springs shown in Fig 4.1, together with the nodal forces and restraint indicated, will generate a system of linear equations identical to the first matrix above.

Fig 4.1: Two connected springs with restraints and loads shown.

It follows then that the solution of this structural system will be very sensitive to the stiffness of the red spring. It turns out (in this case) that the solution is also relatively insensitive to the stiffness of the blue spring: a 100% change in that spring’s stiffness results in only a 0.2% change in the solution! (This is left as a verification exercise for the reader.)

Why Does it Happen? In this example, ill conditioning has arisen because the matrices are nearly singular. In mathematical terms, the two equations are nearly linearly dependent, i.e. one equation is almost a linear ratio of the other; in the above matrices, the second equation is approximately –1.0 times the first equation. In structural terms, the ill conditioning has occurred because of the large relative difference in the stiffness of the two springs; the addition of the second spring makes little difference to the matrix so its significance is almost lost.

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The term “condition” is actually a mathematical term. Most books on numerical methods will cover the so-called condition number of a matrix and show that the higher the condition number the more ill conditioned the matrix becomes. The condition number is related to the ratio of the magnitudes of the maximum and minimum eigenvalues of the matrix; in a matrix with zero eigenvalues, the condition number is infinity, that is, the matrix is singular.

Although a low condition number usually means high solution accuracy, a high condition number does not always mean low solution accuracy. The condition number provides a lower bound of precision, which is often pessimistic. More information on this can be found in texts on numerical methods.

Ill Conditioning and Numerical Precision Although both solutions for the above matrices are exactly correct for the given coefficients, that is, neither matrix is actually singular, if we truncate all the coefficients to three digits, then both matrices will become singular and cannot be solved.

This is a very important point with reference to FEA because the equations are stored and solved using a finite precision on a digital computer. Strand7 uses so-called double precision, which stores a real number using 8 bytes, providing around 14 digits of precision. Fourteen digits sounds like a lot of digits, but it is not difficult to generate matrices with large differences in coefficients even for physically meaningful structures.

For example, a plate element representing a 5mm thick steel plate will generate coefficients corresponding to the in-plane stiffness of the plate of the order of 1.0E9 while the coefficients corresponding to the bending stiffness will be of the order of 2.0E3 (using SI units): a relative difference of six digits.

Loss of precision due to the number of digits required to store, i.e. represent, the real numbers is only half the story however. The other half is the so-called round-off error that is generated and accumulates during the matrix decomposition (solution) phase.

In the above, we have assembled two ill conditioned matrices with sufficient precision to fully represent the information (4 digits). We have then solved the matrices with sufficient additional precision to ensure that the solutions obtained are accurate. If during the elimination process we operate on numbers of very different magnitudes, we progressively lose digits of precision in the result. Consider the following example:

Working with four digits of precision, we add the number 1.234E3 to the number 1.234E0: the result becomes 1.235E3 which means we have effectively lost three digits of precision.

What Does this Have to do With my Analysis? Ill conditioning can have detrimental effects on any analysis, possibly generating unreliable results. Ill conditioning can also be very problematic in nonlinear analysis where it could have a significant effect on convergence rates and levels. For example, it is possible to devise an FEA model where the convergence tolerance will never get below a certain value no matter how many iterations are used, even if the solution has basically converged.

What Causes Ill Conditioning in FEA Models? The following are some examples of where ill conditioning might occur:

• An element or a group of elements respond to loads with large rigid body motion but little deformation. This could be something that is not restrained properly or a very stiff part that is supported entirely by significantly more flexible elements.

• Thin shell models where the tensile stiffness is much higher than the bending stiffness.

• Models with two materials that have Young’s moduli differing by several orders of magnitude.

• Short beam elements with high Young’s modulus and large section areas used to represent quasi-rigid connections.

• Highly distorted or high aspect ratio elements.

• Overly stiff supports.

• Overly stiff contact elements. In most cases it is very useful to activate the Dynamic Stiffness option and let Strand7 determine the most appropriate stiffness value. This may sometimes increase the number of iterations required, but usually will produce more accurate results.

Did you know?

Hide Zeros 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 at 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.

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In most cases where very stiff parts of a structure are required, replacing the stiff elements with Rigid Links will reduce the ill conditioning.

Identifying Ill Conditioning in Strand7 The Strand7 Log File Viewer can help you identify some of the tell tale signs of an ill conditioned matrix. The following should be checked:

• Warnings about rigid body motion (the possible modes will be reported).

• The ratio between the maximum and minimum pivots.

• Any reported negative diagonals. This indicates an unstable structure and the source of the negative pivot should be investigated.

• The maximum displacement magnitudes to ensure that they are are not abnormally large. Note that if all your Young’s moduli are out by an order of magnitude, then in a linear static analysis your displacements will also be out by an order of magnitude, but your stresses will not be. Looking at only the stresses will not reveal an error in the Young’s modulus.

The point made about the definition of the condition number is also useful because we can look at a natural frequency analysis to see if there are any zero (or near zero) frequencies. Although it is generally not possible to get the highest eigenvalue to calculate an actual condition number, a zero eigenvalue will usually point to a free structure (or part of the structure)

Application PALI This application has been developed by Engin Soft S.p.a. (Italy) for Tecnopali S.p.a. It is part of a financed regional research project named “multi-objective optimization of steel poles”. It consists of two modules:

1. Pole Calculation Module (PALI)

2. Load Calculation Module (VENTO)

The main aim of the application is the structural calculation and verification of a geometrically nonlinear steel pole subject to static, wind and seismic actions according to various international codes.

The main application is divided into two parts:

1. The first part generates all external loads according to the selected international design code.

2. The second part interacts with the Strand7 API to create a parametric model of the steel pole, apply the loads, run the Strand7 solver, and generate all the results required for post-processing and verification.

The Strand7 API gives access to almost all the functions available through the graphical user interface. In addition,

a large number of parameters can be dealt with very efficiently via the API, including:

• General tapered cross section with welded, flanged or slip-joint connections.

• General piecewise distributed load for wind actions in all directions.

• Fast handling of non-linear increments with load multipliers derived from different limit states codes.

While the PALI input files are text files (eventually these may be generated through a web interface) the output can be given in different formats such as:

• Text File

• Excel Spreadsheet

• General Database (via SQL)

It is thus possible to keep track of each calculation performed. If required, the storage of results may include the original Strand7 model file containing the parametric FEM model. This model is available for the extraction of any result which is not directly found within the PALI output file.

Figure 4.1 illustrates the data flow within the application. Geometry and design code inputs are text files, with PALI and VENTO both Windows EXE files (console applications which run in batch mode). In addition to the Strand7 API DLL, another DLL provides a library of common functions used by both PALI and VENTO. The application is written in Delphi.

Figure 4.1: Flowchart of application.

Figure 4.2 shows a typical Strand7 model automatically generated with PALI. This example represents a 12m high tapered steel pole.

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Figure 4.2: Typical Strand7 model of pole, automatically generated.

The Strand7 Finite element analysis environment has thus been used, within the same company, to address two different tasks:

1. Using the Strand7 interface, a general FEA software system is available to perform global or detailed calculations (e.g. regarding stress concentrations at openings or base plate design, etc).

2. Through the interaction with the Strand7 API, very fast global calculations of known products can be performed with only location and pole geometry as input parameters.

This application can also be used within a general optimization environment to reduce cost and/or weight of new products or even to generate catalogues for different sites

For additional information:

Daniele Schiavazzi d.schiavazzi@enginsoft.it

North Kiama Bypass TechSpan

North Kiama Bypass

Say Kiama and people know what you are talking

about: a beautiful township, two hours south of Sydney. Stunning beaches, lush green mountainous surroundings, little craft shops, cafés and of course the widely renowned spectacular “Blow hole”. Say Kiama at the Reinforced Earth Company’s office and RECO’s successful team of Designers, Engineers and Draftsmen think of something completely different: Challenging; Multi Disciplinary; Technically complicated; Race against the clock, in short: every possible reason why people can rely on The Reinforced Earth Company for their projects.

Currently, this popular area is only accessible by a winding two-lane road through North Kiama and is subject to major traffic delays. In 1986, it was decided not to proceed with the widening of the Princess Highway thus resulting in the “North Kiama Bypass”. The first stage, a concrete bridge across the Terragong Swamp is already completed. RECO’s involvement in the second stage of this $141 million dollar project comprises a 64-metre long railway tunnel, 2400m² TerraClass wall area and another 1270m² of temporary wire wall to enable the diversion of the Princess Highway through various stages of the project.

The railway tunnel replaces the existing level crossing through the Princess Highway. The design of this tunnel was a major feat. The tunnel was restricted in every imaginable way: the radius of the track, road width and reduced level of the road, yet trains had to fit through, without hitting the tunnel, determined by a clearance envelope. 3D-drawings were created in order to determine whether the train would have a trouble free passage through the full length of the tunnel. Tunnel elements had to be modified and truncated. Both ends of the tunnel were curved inwards, creating more challenges: How to cast these units? Would they fit and fall into place during the installation of the tunnel? The end result was 86 units in total, 70 full size units, 7 half units, 9 wedges of which none are identical.

The rail overpass tunnel concept was developed by Brian Bourne Bridge Engineer Pty Ltd - as the structural consultant to Hughes Trueman Consulting Engineers. Head contractor John Holland Pty Ltd awarded RECO the contract for the detailed design and supply of the precast concrete arch tunnel and the associated reinforced soil walls. RECO engaged Interactive Design Services for specialized design assistance for the arch and Cardno MBK for independent design verification.

Did you Know?

Did you Know Items on the Web Do you have a vague memory of a Did you Know from a previous News.st7 that you think would be useful to your project but can’t quite remember the details. Strand7 Did you Know items are now available on our website www.strand7.com/didyouknow.htm. Updated with each issue, this means that all those snippets of information can be accessed from one centralised location.

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Fig 5.1: Plan of the splayed end structure showing wheel load positions.

Fig 5.2: Deformed shape under M1600 load, 200 times magnification.

Initial analysis and design of the arch shape was carried out using RECO’s in-house software. Preliminary design of the splayed ends of the arch used 2D plain strain analyses with various assumptions to model the 3D effects, but for the final design, it was decided that a full 3D finite element analysis of the structure and the

surrounding fill using Strand7 was necessary to give adequate confidence that the behaviour of the structure was modelled adequately.

Extensive use was made of the API both for generation of the model, and for extraction of results. The 3D coordinates of the centre-line of each arch panel was generated in an Excel spreadsheet, and a series of beam elements were created in the model using the API. The beams were then extruded in two directions to form eight-noded plate/shell elements, and the plate nodes were extruded to form successively: offset beams, master/slave links, and frictional contact elements. Having defined the position of the soil/structure interface the generated coordinates were read back into a spreadsheet using the API, where the remainder of the model was generated. The backfill was divided into eight layers, connected with master-slave links, so that the actual backfill sequence could be modelled in stages. Each fill layer was allocated its own Freedom Case, with every node restrained against movement, so that the fill layers could be fixed in space until they were connected to the model.

The analysis was controlled through a spreadsheet, using the API. The procedure for each layer was:

• Disable Freedom Case restraining the current layer nodes

• Add in master/slave links to connect the layer to the rest of the model

• Run non-linear analysis using the re-start file from the previous layer

• Apply gravity loads, add compaction loads, remove compaction loads

Finally design vehicle wheel loads are applied to the top surface of the fill, and the final arch actions are extracted.

Fig 6.3: View of the North Kiama Tunnel under construction.

For more details of this project contact Paul Quach at Reinforced Earth Pty Ltd, Tel: + 61 2 9910 9930; pquach@reco.com.au, www.reco.com.au, and for details of the Strand7 analysis contact Doug Jenkins at Interactive Design Services, Tel: + 61 2 9940 3414; dougjenkins@interactiveds.com.au, www.interactiveds.com.au

Did you know?

Whiteboard 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, e.g. plate area, brick volume, etc.

Making Finite Element Analysis Easier

www.strand7.com 12

The Strand7 Training calendar for the second half of

2005 has been released. This calendar includes the usual array of courses as well as dates for courses in Perth and the UK.

2005 10-14 Oct Perth Strand7 Course 8-11 Nov Introducing Strand7 15-16 Nov Structural Analysis 17 Nov Automeshing 18 Nov Introduction to the Strand7 API 14-18 Nov UK Strand7 Course

Following from the success of our Strand7 Melbourne course, and based on feedback from users in Brisbane and Perth, dedicated courses in these capital cities by our trainers was deemed a primary goal for the second half of 2005. The Brisbane course has just been presented with a full capacity of participants attending on each day. The Perth course is now beginning to fill up, so if you are interested in attending one or more of the modules (Strand7 Essentials, Nonlinear Analysis or Dynamic Analysis) please contact us.

In late June we also presented a Strand7 training course in Boston, USA for a group of local Strand7 users. As the number of Strand7 users in the USA continues to grow, we have more courses planned in various cities of the USA in the near future.

We would like to take this opportunity to thank all those who attended not only our Melbourne, Brisbane and Boston training courses, but also our in house training courses. Your positive and enthusiastic response during lessons makes teaching an easy and enjoyable experience.

If anyone would like to register their interest in any of our external courses please contact us at info@strand7.com. Details on Strand7 Training Course content can be found on our website at www.strand7.com/training.htm

Head Office Strand7 Pty Ltd Suite 1, Level 5 65 York Street Sydney NSW 2000 AUSTRALIA Tel +61 2 9264 2977 Fax +61 2 9264 2066 Email info@strand7.com Web www.strand7.com

Strand7 continues to exhibit at a variety of exhibitions

across the globe. These are a great opportunity for us to meet not only potential new users but catch up with our existing users.

22-24 Nov 2005 Civils 2005 National Hall, Olympia, London, UK – Stand J18

From November 22-24, Strand7 will have a booth at Civils 2005, the UK’s number one civil engineering showcase being held in the National Hall, Olympia, London.

We are also planning to attend other exhibitions in the USA, so keep watching our website news pages to check if we are planning to visit a city near you

Strand7 User Profile

Doug Jenkins Interactive Design Services

Q – How would you describe your business?

A small civil engineering consultancy, specialising in the analysis and design of bridges, buried structures, retaining walls and related structures.

Q – What types of jobs do you use Strand7 for?

Analysis and design of structures, particularly soil structure interaction and seismic analysis.

Q – How does Strand7 help you in what you design and analyse?

The use of plate and brick elements together with non-linear materials models and re-start files allows soil-structure interaction problems to be analysed much more realistically than simplified approaches.

Q – What features of Strand7 do you find most useful?

I find the API very useful in setting up complex models efficiently, and the post-processing and animation facilities are very useful for visualising analysis results.

Contact Details Doug Jenkins Interactive Design Services Pty Ltd Tel +61 (0)2 9940 3414 Fax + 61 (0)2 9940 6330 Mobile +61 (0)414 854 402 Web: www.interactiveds.com.au e-mail: dougjenkins@interactiveds.com.au

Training Exhibitions