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News.St7

Strand7 Release 2.3 Launched! This month sees the launch of a new major release of Strand7.

This represents yet another leap forward in functionality, with new features in virtually all areas of the software. While many of the new features have been developed in response to user requests, there are also a number of novel additions such as the string group.

In this newsletter we highlight two of the new features. For full details please take a look at the “What’s New” article which you can find on our web site: www.strand7.com/whatsnew23.htm

We value your feedback and have set up a dedicated service to handle your comments. We would be very pleased to hear from you with any comments on this release and also features that you would like to see developed in the future. Please call us or send your feedback to: news.st7@strand7.com

Welcome to the first edition of our newsletter for 2004.

We would like to thank all of our readers for the positive and useful feedback that we received after the publication of our last issue.

We are delighted to announce Strand7 Release 2.3 and know that you will benefit from the new features. As always, enormous effort has gone into the development, testing and documentation, all of which you will find meets the usual high standards that you have come to expect from Strand7.

In this issue of News.St7 we have continued with the theme of issue 1, by providing information and articles that hopefully you will find interesting and useful. This issue sees the continuation of the benchmarks and modelling tips and at your request includes even more ‘did you know’ items!

The Strand7 Theoretical

Manual is almost complete and will be available in the very near future.

The manual will provide users with a thorough foundation in all of the theory utilised by Strand7.

Please keep an eye on our web site for a release announcement.

If you have any feedback or suggestions regarding the content of News.St7, or you would like to have your latest project included in the “Current Projects” section then please email: news.st7@strand7.com. If you would like to receive your copy of News.St7 directly by email, simply send a blank email to: newsletter-subscribe@strand7.com

2.3 New Features Summary New IGES Import Options New 2-Point Link Element

Load and Freedom Case Enhancements Inertia Relief

Quasi-static Seismic Analysis New Element Attributes

New Model Construction Tools Create Composite Material Libraries

Identify Link Free Ends Load Patch Element

String Group Convert Time Domain Data to Spectral Curves

New Harmonic Solver Options Powerful Enveloping of Results

FFT Analysis for Dynamic Problems 100 New API Functions

Functionality and Help Improvements

In this issue… • Release 2.3 highlights 2

• Exhibition USA report 4

• Recommended hardware 5

• Current projects 7

• Modelling tip 11

• Benchmark 12

• Training calendar 14

• Exhibitions calendar 14

Theory Manual

Issue 2, May 2004

Editorial

Newsletter for Strand7 and Straus7 users Strand7 is marketed as Straus7 in continental Europe

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There are far too many new features and functions in

Strand7 Release 2.3 to adequately describe them all in this issue of our newsletter, so instead we focus on just two of them. Detailed descriptions of the others can be found in the latest Strand7 Online Help. The Load Patch The load patch is a plate element that is used for transferring area loads and mass (such as pressure and non-structural mass) onto a framework of beam elements. In its simplest usage, a pressure load applied to a load patch is transferred to four beam elements connected to the four edges of the plate. To use a load patch, you set the property type for the plate to Load Patch and then assign one of the load patch attributes to the plate. You can see that the property dialog below has none of the usual property data (such as modulus).

The load patch has no stiffness and no mass (although mass attributes can be assigned to it), so its inclusion in a model does not affect the stiffness or mass of the structure you are analysing. This implies that without the application of plate attributes, a load patch element is basically redundant. The way in which the patch loads are transmitted differentiates the load patch from a normal plate/shell element. The plate/shell element converts its loads to a consistent set of forces and moments that are applied only to its nodes. The load patch however, converts its load (and mass) attributes to distributed loads (and mass) applied directly to the beam elements (not the patch nodes) connected along the edge of the patch. In other words, you will not obtain the load patch result by using a plate/shell element with a zero modulus to transfer pressure loads to beams.

The conversion of plate load to beam load depends on the load patch attribute assigned to the load patch plate. There are six different load patch attributes (shown below) and these control both the proportion of load applied to each edge and the distribution.

For example, Type 1 distributes the patch load to the beams on all four edges of a quad element (or three edges of a tri element) according to the tributary area associated with each edge. In the case of a rectangular load patch, two opposite edges will be assigned a triangular beam load and the other two edges will be assigned a trapezoidal load. The figure below illustrates this.

An important feature of the Strand7 load patch is that if the beams along its edge are subdivided, a single patch is still sufficient to correctly distribute the load to the beams. In the figure below, the long beams have been subdivided into 8 elements and the short beams into 5.

Conversely, the load patch may rest on part of a beam and the appropriate load is then applied to that part of the beam covered by the load patch. Many of the attributes that are supported by plate/shell elements can be assigned to load patch elements for conversion to equivalent beam attributes (including pressure, shear and non-structural mass). This conversion is performed automatically (and transparently) at the commencement of the solve. There is also a tool to convert the patch attributes to actual beam attributes if you prefer to see the beam loads before solving – in this case you could delete the patch plates after conversion.

Release 2.3 Highlights

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Finally, to facilitate the application of patch loads to complex frameworks, especially 3D frameworks, the Create Load Patches tool can be used. This tool searches for convex connections of (at least 3) beam elements in a framework and automatically creates one or more patch plates, depending on the geometry. The String Group This is a very exciting addition to the capabilities of Strand7, which allows easy modelling of a string or cable type of element that is fed through one or more pulleys within a structure. Consider the following very simple example:

Point A is fixed and at points B and C there are frictionless pulleys through which a cable (string) passes. To model this situation in Strand7, we connect together three truss elements to represent the segments of the string and then group these elements together by assigning a String Group attribute to them. This information tells the Strand7 solver to treat the three truss elements as a continuous string that can slide freely over the pulleys. The pulleys in this simple case are just fixed node restraints. The following figure shows the solved Strand7 model. A single point mass acted upon by a 1g acceleration represents the weight. The blue lines represent the string (truss elements) and the red lines are the axial force diagram.

As the figure illustrates, the axial force in the three elements is the same. Had this been run without the string group attribute, then we would have found zero force in the two elements on the left hand side. There are many other more important applications for the string element, including the following: External post-tensioning of a concrete bridge beam Post-tensioning is a popular technique used in the construction industry to improve the performance of a

structure and increase its load carrying capacity. Consider the figure below, showing the simple arrangement of a concrete beam post-tensioned by a single ungrouted tendon.

A Strand7 model of this beam and tendon is now very easy to construct because no special procedures are needed to model the freely sliding tendon. Simply define the tendon by a series of truss elements (four were used for this model) and group these all together with a string group attribute. The figure below shows an exaggerated display of a Strand7 brick and tendon (string group) model, subject to the tendon tension only. The tension in the tendon is constant.

Erection of a deployable structure The figure below shows three steps during the erection procedure of a frame structure. In this example, a tendon (shown in red) is fixed to one end of the structure and passes though a series of frictionless pulleys through the base of the structure. The tendon is tensioned from the free end and this allows the structure to take up its desired shape.

In this model, the tendon is modelled with eight separatetruss elements, all grouped together under the same stringgroup. The tension is applied via a prescribeddisplacement pulling the free end of the tendondownwards. In this first release of the string group, the pulley throughwhich the string passes is assumed to be frictionless. Afuture release of Strand7 will allow pulleys with friction tobe modelled

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In the past few months we have exhibited Strand7 at

several conferences in the USA, China and India.

We are pleased to report that Strand7 was very well received all round. We have had strong interest from engineering companies operating in all of the mainstream engineering disciplines and also in several of the more specialised fields.

Strand7’s popularity stems, in part, from the fact that whilst it is described as “general purpose” FEA software, it contains advanced features that are usually only available in premium priced FEA packages.

NASCC 2004 Steel Conference, Long Beach, USA.

Many of the interested parties were very pleasantly surprised to discover the depth of analysis that Strand7 can perform. As always, the Windows-native and intuitive feel of Strand7, combined with functionality and incredible value for money were big winners!

Pacific Design & Manufacturing Show, Anaheim, USA.

In the USA, China and India, Strand7 has been purchased by clients working in areas of marine, structural composites, structural and automotive engineering, and by a number of universities and polytechnics. The list is ever growing.

Our move into these new markets is coupled with a significant increase in resources available to our research and development and technical support teams. Therefore we have many new exciting features planned for future Strand7 releases.

In conjunction with our recent shows in the USA and China, we are pleased to announce the appointment of two new Strand7 distributors:

Beaufort Analysis Inc has been appointed as a Strand7 distributor in the USA. They can be contacted at:

Beaufort Analysis, Inc. 111 Safrit Drive Beaufort, NC 28516, USA Tel: +1 252 422 0104 Email: info@beaufort-analysis.com Website: www.beaufort-analysis.com

Sizhuanda Co. Ltd. has been appointed as a Strand7 distributor in China. They can be contacted at:

Sizhuanda Co. Ltd. 115 Fucheng Road, Haidian District, Beijing 100036, China Tel: +86 10 8811 2908 Fax: +86 10 8811 0350 Email: info@strand7cn.com Website: www.strand7cn.com

Find out more about future exhibitions in our section onthe back page. Our exhibition schedule is also regularlyupdated on the Strand7 website: www.strand7.com

With the ever increasing popularity of Strand7

worldwide, we are pleased to announce that the Strand7 interface is now available in Chinese and Japanese.

Chinese Interface

Japanese Interface

Chinese and Japanese Interfaces

Exhibitions - Report

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The objective of this article is to identify those

components of a computer system that have the greatest effect on the performance of Strand7. This article is aimed at the Strand7 user who is on a budget and wants to spend money on the components that count.

Our support team frequently gets enquiries regarding the best computer specification to purchase. There is no doubt that with an unlimited spending budget, you will get the best computer with the best performance. However with the rapid rate of technology progression, what is the best now will most certainly be superseded within months if not weeks.

With this in mind, it is usually not cost effective to pay for the fastest and most powerful computer system on the market as they attract a higher premium. Consider buying the next best. They will often be substantially cheaper yet suffer only slightly in the performance stakes.

The two components that affect the performance of Strand7 the most are the CPU and the RAM.

Other factors contributing to the overall performance of Strand7 are also discussed.

The CPU

In terms of Strand7 performance, the most significant attribute of the CPU is its clock speed.

The two dominant CPU manufacturers are Intel and AMD. At the time of writing the Intel Pentium4 2.8GHz HT and the AMD XP2800+ appear to represent the best value for money.

Strand7 includes code specifically optimised for each of these CPUs so you can rest assured that no matter which CPU you choose, Strand7 will be performing to the best of the CPU’s ability. In Strand7, go to File/Preferences and click on the Solver tab to see how Strand7 has identified your CPU.

The RAM

The Random Access Memory (RAM) is where most of the CPU temporary data is stored. Data which fills up the RAM will spill onto the computer’s hard drive for temporary storage. Access to data stored in RAM is extremely fast compared to access to data stored on the hard drive. If possible we want to minimise spillage onto

the hard drive and exclusively use the RAM as temporary storage. This simply means that the more RAM you have, the better.

At the start of a solver run, Strand7 reports the optimum amount of RAM needed for the model. If you have significantly more than the reported optimum amount then you can be sure that your model calculations are not being slowed down by access to data on the hard drive. The reason you may need significantly more is that Windows itself utilises a portion of RAM for the operating system and background tasks.

A point to note is that Windows can only utilise a maximum of 4GB of RAM. However a single process, such as Strand7, is only allocated a maximum of 2GB RAM, no matter how much RAM is on the system. Installing more than 2GB is still an advantage however, as this provides Windows with memory which can be used for other functions such as disc caching, multitasking etc.

Windows also provides its own virtual memory management via a so-called swap file so that if insufficient RAM is available, the hard disc is used instead. The system setup tools in Windows offer the option to manage the swap file automatically or to fix its size manually. In most cases, Strand7 (and other applications) will run more efficiently if the swap file is set to a fixed size. Fixing the swap file size to twice the

amount of RAM on your system is usually a good setup.

The Video Card

Installing a good quality video card will noticeably decrease the time it takes to refresh a model on screen in the Strand7 pre and post-processing environments.

Did you know? Transparent User Stress Limits 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.

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Dynamic rotations will also be much smoother.

Speed enhancement can be achieved by reducing your screen colour depth to 16 bit from 24 or 32 bit. There is very little noticeable difference to the naked eye and the processing overheads are dramatically reduced.

The Motherboard

The motherboard is responsible for the communications between the various components of your computer system.

The Front Side Bus (FSB) speed is the most significant attribute of the motherboard specification.

In terms of Strand7 performance, the faster the better.

The Hard Drive

The hard drive is used to store files. Strand7 needs to store the model and results files and also the files that are created during the analysis. Most of the analysis files are temporary and hence their creation and deletion is “invisible” to the user.

Your hard drive needs to be large enough to store these files.

In large models, the solver and results files can be quite large – especially in transient dynamic analyses.

The largest temporary analysis file is usually the matrix file. At the beginning of the solution the solver reports the matrix size and also the “free scratch space”. If the free scratch space is not large enough then the solution will

terminate and an error is reported.

If the files being written are large then the disk speed will noticeably affect the solution time. The disk speed also has an effect when there is insufficient RAM available and the hard drive is used as “virtual memory”.

With the price of hard drives falling, it is advisable that a minimum size of 80 GB is selected with disk speeds ≥7200 rpm.

To get the best performance out of your hard disc, we recommend that you regularly perform a disc defragmentation. You should also be aware that if you write to result files across a network then the write time can significantly increase.

Purchasing

Although building your own computer system can give cost savings, if you are not confident, it is advisable that you let an expert computer technician do it for you. If you purchase a complete system, you usually obtain more comprehensive warranties and benefit from more comprehensive testing of component compatibility.

It is wise to purchase from companies that will provide good after sales support. These companies should have well supported software/drivers and are more likely to release service fixes if problems are found.

After reading this article you should know how a specific component of a computer system affects the performance of Strand7. If you need any further information then please contact our support team

The Strand7 API was released mid 2003 and is

already being used by many users.

We have received several requests to set up a data exchange catalogue containing examples of user applications. We are now in the process of compiling this catalogue which will soon feature on the Strand7 website.

We will provide summary details of the API application developed and details of the developer who can be contacted for further information.

Unfortunately, at this stage, we are not in a position to verify the accuracy of each user’s application.

If you would like to include your application in this catalogue then please send us your contact details and we will forward you a short Application Description Form to fill out.

Please send the information to: api@strand7.com

Did you know? Space - Shortcut to toggle selection arrow

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 pointer to toggle the arrow. Simply hit 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.

API - Users Application Catalogue

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In this section we present current projects where Strand7

is being used to perform FE analyses. Projects from both Strand7 users and our own Strand7 Consulting are presented.

Our thanks go to Outokumpu Pty Ltd, Crib Point Engineering and Enmin Pty Ltd for their contributions to this issue.

If you would like to have your project included in the next edition of News.St7, please email: news.st7@strand7.com

Goro Nickel Project

Outokumpu is the largest provider of mineral processing technology in Australia. In 2002 they were awarded a contract for 9 paste thickeners for the Goro Nickel Project in New Caledonia. These thickeners are 20m in diameter with a 10m sidewall above a conical floor section which makes the tanks almost 20m tall. All structural aspects of the thickener were modelled using Strand7 including the high torque rake drive unit, the drive shaft, raking mechanism, the bridge structure, tank and support structure.

Cutaway general arrangement of thickener

The drive shaft and raking mechanism model was created in AutoCAD Inventor as a solid model and imported into Strand7 where it was automeshed with plate elements. This method was perfectly suited to the geometry as it had numerous pipe to pipe intersections at different angles which would have been particularly difficult to model manually. Making changes to pipe sizes and orientations was extremely easy and a great deal of time was saved using the automeshing tools.

The tank and support structure was modelled as a complete unit which allowed for accurate footing loads to be extracted for all load cases.

FEA seismic reaction (inertia force) contour plot This was particularly useful when the client requested the calculation of the individual footing loads resulting from the application of the predicted settlement of the floating foundation slab. G+D Computing recommended using prescribed displacements, as specified by the client, to tackle this challenge. This method then allowed Outokumpu to quickly check for any stress concentrations and also create a datasheet showing individual footing loads for a series of slab settlement cases. At the completion of the project, the client expressed their appreciation in writing for the timely manner in which Outokumpu was able to answer the numerous requests for detailed footing information. This would not have been possible had the structure not been modelled using FEA.

Once fabrication of the equipment had started in the Philippines, the client requested that Outokumpu assess the possibility of transporting the tank and mechanism as a complete unit to site in New Caledonia. As the component models were already constructed, they were joined together and this allowed Outokumpu to inform the client of the exact centre of gravity of the structure and also design transport beams that would allow two large crawler trucks to transport them over the final journey by road to the processing plant.

Did you know? Applying Attributes 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.

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At present, the fabrication portion of the contract is complete and is awaiting client approval for final assembly and shipping to site. You can obtain more information about this project from Hamish Mackie, Outokumpu Pty Ltd. Tel: +61 2 9984 2500 Fax: +61 2 9984 2501 www.outokumpu.com.au

VLocity Traction Engine Beams

Crib Point Engineering were contracted by Cummins to design and manufacture the main traction engine support beams for the new VLocity trains which will be operated throughout Victoria, Australia.

Crib Point Engineering employed the specialist services of Strand7 Consulting to perform a Finite Element Analysis to investigate the required proof and ultimate loads and also to perform a fatigue evaluation.

The preliminary design configuration was taken from previously designed traction engine beams. For this project, changes were made to several areas, but most

significantly to the governing loads, acceptance criteria, engine mass and panhard rod configuration.

The FE model consisted predominantly of Quad4 shell elements. Rigid links and lumped masses were used to model the engine, transmission and drive shafts. Spring/damper elements were used to model the isolation bushes used at six connection points within the drive system. Contact elements were introduced to accurately model contact faces and restrict excessive movement in certain locations under the ultimate loads.

An initial FE assessment was performed. 26 load combinations were considered for the proof loads and a further 26 for the ultimate loads.

These loads considered all of the possible combinations of positive and negative accelerations in the longitudinal, transverse and vertical directions.

Following the initial assessment, areas were identified that required modification and optimisation to meet the design requirements.

Under close cooperation between G+D, Crib Point Engineering and Cummins, various remedial options were investigated.

All of these options considered constructability, code compliance, potential clash with ancillary components and significantly the maximum permissible weight for the entire system.

This iterative process was first completed for the proof loads and subsequently for the ultimate loads.

Proof load acceptance was governed by maximum stress criteria whereas the ultimate analysis

considered both material and geometric nonlinearities to ensure that gross failure and progressive collapse of the

Did you know? CTRL-Click Edit Nodes 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.

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structure did not occur.

Finally, a fatigue assessment was made in accordance with BS7608. Principal stress ranges were determined for the applied fatigue loads. Each structural detail was classified in accordance with the code and a fatigue life calculated based on the summations of the fatigue damage caused at each location under each load case.

The final configuration of support beams has resulted in a design that has been optimised for fatigue life and structural performance whilst minimising construction costs, manufacturing time and overall weight of the system.

You can obtain more information about this project from Sean Turnbull at Crib Point Engineering. Tel: +61 3 5979 1703 Fax: +61 3 5979 3323 www.cpe.net.au

Vibratory Feeder

Strand7 Consulting was employed by Enmin Pty Ltd to investigate the structural integrity and estimate the design life of a new support frame design for one of their vibratory feeders.

Enmin provide materials handling solutions via a range of vibrators and flow aid devices which are designed and manufactured in-house.

The vibratory feeder under investigation is driven by a pair of eccentric mass vibrators. These are operated in-phase but in opposite directions. This results in the oscillating vibratory action occurring predominantly in one plane.

Enmin supplied Strand7 Consulting with CAD files which were converted into mid plane models and subsequently imported into Strand7 where the geometry was cleaned and automeshed. A predominantly Quad4 plate mesh was created. Isolation bushes were modelled with spring/damper elements.

The new design required that there be clear space under the front of the feeder. The design should also allow the feeder to be easily cleaned, be visually appealing and provide minimal areas for spilt material to collect.

The general arrangement of the feeder model is shown below:

A nonlinear transient dynamic analysis was performed. This allowed an investigation of the full start-up and operational cycle.

A factor versus frequency table was created to replicate one start-up cycle followed by constant speed operation. The graph over the page shows the changing amplitude (force) and frequency (motor speed) with time over the start-up period.

Did you know? Right-Click Attributes 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 box, right-click to bring up a list of attributes to choose from. Select Force and you will find that the Nodal Force Attribute is now the active dialog box. It’s that easy. This works for all attribute types in Strand7.

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Stress ranges were calculated for the start-up and continuous operation speeds. These values were assessed in accordance with the British Standard for fatigue assessment.

The fatigue life was estimated based on the cumulative effects of start-up, shutdown and continuous operation.

Some areas were identified that required modification to achieve the desired design life. It was also found that the structure had a significant mode of vibration with a frequency close to the operational speed of the feeder.

In conjunction with Enmin, the feeder design was optimised to reduce stress ranges and shift the vibrational modes away from those encountered at the normal operational speeds. This was achieved by redistribution of mass using local plate thickness changes and also changes to the stiffness of the main joint connections.

An example of the plate principal 11 stress plot is shown:

The final optimised design is now in successful production.

Further details can be obtained from Glenn McTaggart at Enmin Pty Ltd. Tel: +61 3 9753 3633 Fax: +61 3 9753 3796 www.enmin.com.au

Strand7 Consulting provides expert FEA services for engineers. For more information on the services provided please contact:

Steve Raynes at Strand7 Consulting Tel: +61 2 9264 2977 Fax: +61 2 9264 2066 www.strand7consulting.com

Did you know? Verification Manual 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.

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In this issue we will briefly discuss the modelling techniques that can be employed to model a fillet weld connecting two

perpendicular plates. There are generally several approaches to model any connection. The connection configuration and level of accuracy required will dictate the appropriate modelling technique. The methods outlined below are the most commonly used to model a fillet weld and a brief appraisal of each method is given.

*Please note that the mesh densities shown are for illustration purposes only.

1. Two intersecting plates 2. Increase thickness of plates in the weld zone

3. Model the fillet weld material with plates

4. Use a full brick model

This method of modelling a welded joint is by far the simplest and most efficient. If you had a large model with many welded connections then this would be the most practical method. Note that the stresses should be considered at a specified distance from the weld/plate intersection.

This method is still relatively simple, yet takes accuracy levels a step further. The additional plate thickness more accurately models the weld stiffness and the effective plate spans.

This method is used when you want to distribute the load to the actual area of the weld and consider the additional stiffness of the weld material.

It is also possible to model the free edge between the red/blue plates where the weld is not a full penetration type.

This method is used when considerable detail about the connection is required.

For clarity, the sketch shows a crude mesh. Mesh refinement would be required for model accuracy.

Pros • Very simple to model; • Good global

representation.

Pros

• Simple to model; • Good global

representation; • Additional stiffness in

weld zone is accounted for.

Pros • Simple to model; • Allows stresses to be

extracted for weld material itself;

• Weld configuration can be more accurately modelled.

Pros

• Can obtain highly accurate results;

• Removes the singularity at the plate intersection;

• The ability to extract results at the weld toe and in the weld material.

Cons

• Singularities at plate intersection;

• Extra stiffness of weld material ignored.

Cons • Singularities at plate

intersections.

Cons • Singularities at plate

intersection (although stress estimation in the critical zones is often simpler than with methods 1 and 2).

Cons • Complex procedure to

model lots of welds; • Solve times increase

dramatically.

Different design codes specify different distances from the weld toe to extract the calculated stresses. Please refer to your specific design code for more information.

If you require detailed results around the weld zone, then it is advisable that you use brick elements to model the welded connection as shown by method 4. Simple comparative models can be run to estimate percentage difference between each of the modelling options. This can be used to justify results calculated via the simpler methods that can be used in larger global models

Modelling Tip

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In this edition we will look at a benchmark problem that formed part of the

submission to the Hong Kong Buildings Department. This gained Strand7 the technical approval required to support structural design submissions to the Hong Kong Building Authority. Subsequently, Strand7 has been used extensively for the design and analysis of various structures throughout Hong Kong.

This particular benchmark problem makes use of the Strand7 geometric nonlinear solver. The solver is capable of analysing structures that undergo large displacements. The problem is defined by a square plate that is clamped at all four edges and is loaded by a uniform normal pressure. The nonlinear displacement and stress response are compared with a published analytical solution.

The reference solution is given in National Advisory Committee for Aeronautics (NACA) Technical Note No. 847, “Square Plate with Clamped Edges Under Normal Pressure Producing Large Deflections”, by Samuel Levy, circa 1940 [1].

The plate is a square plate of edge length 2m and thickness 5mm. The modulus is 2x1011 Pa and the Poisson’s ratio is 0.316. It is clamped at all edges. A normal pressure of 3000Pa is applied incrementally in 16 equal steps.

Benchmark Figure 1 – Symmetric quarter Strand7 model consisting of 4x4 mesh of Quad4 elements

The Strand7 model consists of a 4x4 mesh of Quad4 elements modelling one symmetric quarter. The Quad4 element in Strand7 is a thin plate/shell element based on Kirchhoff theory. It is suitable for the analysis of linear and nonlinear plate/shell problems and has the ability to accurately represent thin shell behaviour, even for elements with a significant amount of warping [2]. This makes it particularly useful in geometrically nonlinear problems because in general, as the elements deflect, the amount of element warping increases.

The displacement and stress at various locations are given as a function of applied load. In each case, the x-axis values are non-dimensionalised by plotting Pa4/Eh4, instead of P, where:

P = Applied pressure

a = Width of plate (2m)

E = Material modulus (2.0x1011)

h = Plate thickness (5mm)

This means that the x-axis values of pressure are multiplied by 0.128 for graphing purposes (24/(2.0x1011*0.0054) = 0.128).

In the graph showing displacement, the y-axis is non-dimensionalised by dividing the displacement by the plate thickness, h = 0.005.

In the graph showing stress, the y-axis is non-dimensionalised by plotting σa2/Eh2 instead of σ. This means that each stress value is multiplied by 8.0x10-7 for graphing purposes (22/(2.0x1011*0.0052) = 8.0x10-7).

Using the customised graphing options within Strand7, it is quite straightforward to normalise the results obtained in the manner described above.

As shown in the figures on the following page, an excellent agreement is found between Reference 1 and the Strand7 results.

In each newsletter we will introduce a new benchmark that users can add to those already supplied with Strand7.

Exclusively to readers of News.St7: You can download this benchmark model from the News.St7 readers’ page of our website:

www.strand7.com/news.st7.htm

Benchmark

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Benchmark Figure 2 – Displacement vs Load from Reference 1.

Benchmark Figure 4 – Stress vs Load from Reference 1.

Benchmark Figure 3 – Displacement vs Load from the Strand7 Result.

Benchmark Figure 5 – Stress vs Load from the Strand7 Result.

References

1. “Square Plate with Clamped Edges Under Normal Pressure Producing Large Deflections”, National Advisory Committee for Aeronautics (NACA) Technical Note No. 847, by Samuel Levy, circa 1940.

2. “Strand7 Verification Manual”, Edition 1, G+D Computing, 2000.

Stress Graph Legend A: Extreme fibre stress ratio at the centre of the plate. C: Extreme fibre stress ratio at the mid-point of an edge of the

plate. E: Membrane stress ratio at the centre of the plate. F: Membrane stress ratio at the mid-point of an edge of the

plate. Note that B and D are not shown on the Strand7 stress graph because they are not automatically calculated.

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This year we have already held the “Introducing Strand7” course.

We have also conducted a number of onsite courses, tailored specifically to the clients’ requirements. Over recent years the demand for these tailored courses has increased, as it allows the course to be focused on the application of Strand7 to the clients’ specific requirements. In addition, there are cost savings for an organisation that needs to train several engineers.

If you are interested in tailored onsite training courses then please contact us for more information.

In June and October we will be running our full series of courses ranging from Introduction through to Structural Analysis.

If you wish to attend one of the courses then check the dates in the calendar and make your booking before it’s too late. You can find full details of the content of the courses, prices and booking form at: www.strand7.com/training.htm

We plan to exhibit at the following conference:

17 – 20 August 2004

China International Steel Construction Expo/Conference

Beijing Exhibition Centre, China

If you get the chance then we would be delighted to meet you and discuss Strand7 with you. You will have the opportunity to meet representatives from Strand7 and from our distributor in Beijing.

We will be keeping you updated on the latest developments in future editions of News.St7

Strand7 Head Office G+D Computing Pty Ltd Suite 1, Level 7 541 Kent Street Sydney NSW 2000 AUSTRALIA

Tel +61 2 9264 2977 Fax +61 2 9264 2066 Website: www.strand7.com Email: info@strand7.com

Training

Exhibitions

2004 1-4 June Introducing Strand7 8-9 June Nonlinear Analysis 10-11 June Dynamic Analysis 15-16 June Structural Engineering 17 June Automeshing with Strand7 18 June Heat Transfer Analysis 12-15 October Introducing Strand7 19-20 October Nonlinear Analysis 21-22 October Dynamic Analysis 26-27 October Structural Engineering 28 October Automeshing with Strand7 29 October Heat Transfer Analysis

Training Calendar