This session covered the application of EC7:

• Slope Stability analysis with a verification case study.
• Retaining Wall analysis with a discussion of how EC7 was implemented using soil structure interaction and finite element analysis to the Florence Rail Station Box.

Both of these sections demonstrate how Oasys Slope and Frew have been developed to simplify the application of Eurocode 7 to geotechnical analysis.

The webinar in December 2011 summarises this session and a link to this webinar is available below.

A copy of the presentation slides are available below:

• Geotechnical Analysis to EC7 – Zeena Farook (Presentation Slides)
• Introduction to Eurocode 7 – Brian Simpson
• Approaches to ULS design – The merits of Design Approach 1 in Eurocode 7

Related Case Studies:

• Hong Kong Cut and Cover Tunnels – Frew Back Analyses
• Advanced Cut and Cover Tunnel Analysis
• The Pinnacle – Foundation Design

This session introduces Eurocode 7, the basis of Geotechnical Design and the applications of Eurocode 7 to spread foundations and retaining structures.

Canton Tower, Guangzhou, China © Zhou Ruogu Architecture Photography

One of my favourite things when I was a child back in the 1970s was an owl made of string. In some regards it was quite simple: two pieces of interlocking hard plastic with notched edges and a ball of golden thread that you had to wrap around. The clever part was that if you started at the top notch on one side, go to the bottom notch on the next, then to the next top free slot, and so on, eventually you had a pattern that, magically, looked a bit like an owl.

Ok, an owl in itself was not that impressive, but what was intriguing to my younger self was that this owl had a double curved surface with curved edges made of nothing but straight lines! As far as I was concerned straight lines were straight and curves curved: that straight lines could produce curves was quite mind blowing. Yes, while others in the 70’s may have taken recreational pharmaceuticals or immersed themselves in the psychedelic art scene, I had a string-art owl.

What I didn’t realise at the time was that I had been introduced to hyperbolic surfaces and their relative: hyperboloid structures.

Why use hyperboloid structures?

Shabolovka Radio Tower ©Richard Pare

So why are hyperboloid structures of interest today? The two main reasons, apart from aesthetic considerations, are strength and efficiency.

As hyperboloid structures are double curved, that is simultaneously curved in opposite directions, they are very resistant to buckling. This means that you can get away with far less material than you would otherwise need, making them very economical.

Single curved surfaces, for example cylinders, have strengths but also weaknesses. Take a drinks can for example: these are made extremely thin, with sides only a fraction of a millimetre thick, yet contain the pressurised beverage and if stood on end can support the weight of a grown adult even when empty. But, once you have enjoyed the contents, you can push in the side with just a slight pressure from your finger. Alternately, if you were to push with your finger from the inside of the can (being careful to avoid any sharp edges of course) then you will find that you have to apply considerable effort to make any impression.

Double curved surfaces, like the hyperboloids in question, are curved in two directions and thus avoid these weak directions. This means that you can get away with far less material to carry a load, which makes them very economical.

The second reason, and this is the magical part, is that despite the surface being curved in two directions, it is made entirely of straight lines. Apart from the cost savings of avoiding curved beams or shuttering, they are far more resistant to buckling because the individual elements are straight.

This is an interesting paradox: you get the best local buckling resistance because the beams are straight and the best overall buckling resistance because the surface is double curved. Hyperboloid structures cunningly combine the contradictory requirements into one form.

History of Hyperboloid structures

Shukhov Tower Nizhny Novgorod 1896

The first designer to make use of hyperboloid structures was the Russian engineer Vladimir Shukhov. Born in 1853, Shukov built his first hyperboloid lattice tower in Polibino, Lipetsk Oblast in the 1890s, and came to international fame with his tower at the All Russia Exposition in 1896.

Over his career, Shukov built over 200 different hyperboloid towers, with typical heights ranging from 12 to 70m. His crowning glory was the Shokov Tower, also known as the Shabolovka Radio Tower, in Moscow. This reached the dizzying heights of 350m, which was 50m taller than the Eiffel Tower yet, at 2,200 tonnes, used only a quarter of the steel.

If you want to know more about Shukov and his place in Soviet engineering, check out the current Royal Academy of Arts exhibition: Building the Revolution (Soviet Art and Architecture 1915-1935), which also features Richard Pare’s magnificent photo of the Shokov Tower as its main image.

Hyperboloid applications

Canton Tower, Guangzhou, China © Kenny Ip

Today the most common application of hyperboloid structures is for power station cooling towers, where the shape enables a minimum thickness of the concrete shell and a boost to the cooling airflow due to the Venturi effect of the cross-section. Hyperboloids have also been used to great effect, both structural and architectural, on a number of recent airport towers (Barcelona) and skyscrapers (Port Tower, Kobe, Japan; Aspire Tower, Dubai; Canton Tower, Guangzhou, China). You can find quite a list on Wikipedia.

Apart from hyperboloid towers (mathematically speaking: a hyperboloid of one sheet), the most common form is that of the hyperbolic paraboloid, or hypar for short, used for roofs.

The hypar is one of the three standard shapes for fabric roofs, the other two being the saddle and the conic. While there was a certain fashion for concrete hypar roofs in the third quarter of the 20^th century, hypar roofs are normally constructed in fabric or cable net. A notable recent example is the London 2012 Olympic Velodrome. The London 2012 Olympic swimming pool and Beijing 2008 main stadium are also hypar in shape but constructed from steel trusses. 

London 2012 Olympic Velodrome © ODA

Modelling Hyperboloids

So how do you create a hyperboloid structure in GSA? There are a number of techniques but they generally involve a twist.

Let’s look at hyperbolic paraboloids first.

• Draw a square or rectangular array of crossed beams, but make sure that all the elements or members are full length: do not split them at the intersection points at this time.
• To make the twist select all the nodes on two adjacent sides, then right click on the middle corner and invoke the Flex command.
• Use a linear flex to move that node up by the appropriate amount and note that all the other nodes, and hence beams, have followed.
• Repeat for the other two sides and you have created your hyperbolic paraboloid.
• To finish simple select all the elements and connect them using the sculpt menu.

Rectangular hypar shells are even easier:

• Take a Quad4 element to cover the whole roof, adjust the corners to the appropriate elevation, then split the warped quad into suitably sized pieces.
• Finish by splitting the Quads into Triangle elements as the Quads will likely be too warped to analyse.

GSA Hypar

The key to hyperboloid towers is the use of cylindrical axes. If you set the current grid (Ctrl+Alt+w) to the Global Cylindrical Axis (or your own as appropriate) you will note that the nodal coordinates are now given not as X, Y, & Z but Radius, Theta (angle) & Z (height). 

Hyperboloid Twist

• Define a node on the top and bottom rings and join with a beam.
• Copy this round to form a circular array (note that the copy command defaults to the current axis set).
• Mirror all the resulting beams through the radius/theta plane (you will see why in a moment).
• Select all the nodes in the top ring and move them through a suitable theta angle (hint: make it a multiple of the beam spacing).
• Do the same for the twin ring at the bottom but make the angle the negative of that you used at the top.
• Select all the lower beams and Move them (not copy this time) back through the radius/theta plane to make them overlap with the original set.
• Select all the beams and Connect them to form the surface.
• To complete the surface, select all the nodes and extrude them by the angle you used to create the beams, including beam elements along the extrusion to create hoops.
• Alternately, trace Quads onto the beam grillage, split them into triangles, and copy them around. Finish by deleting the beam formwork.

Another way to form a hyperboloid shell tower is to create two nodes, one on the top ring and one on the bottom, with one set at an angle. Join the nodes up with a beam, split the beam into sufficient pieces, delete the beams and extrude the resulting nodes around, creating Quads in the process. Finish by splitting the Quads into Triangles. Note that while the surface will be the same as the previous method, the mesh will be in a different pattern. 

Beam vs Shell meshing

Hyperboloid performance

For the purposes of this article I modelled a cooling tower type shell structure, with a 50m radius base, 35m radius top, a height of 120m and a constant 100mm thickness. Real cooling towers have beams at the base, a varying shell thickness and stiffening rings; mine is a simplification purely for illustrative purposes.

When analysing 2D elements it is vital to ensure that you have a sufficient mesh density. To examine the effect I took a hyperboloid geometry with a 90 deg twist (the top ring is twisted 90 deg in relation to the bottom), then modelled the mesh in sizes ranging from 30 deg down to 2.5 deg, and in both Tri3 and Tri6 elements. 

30 degree mesh - 2.5 degree mesh

It is a good idea to halve the mesh and re-analyse to see if it makes any difference to the results. In the case of analysing these structures for self weight buckling the results were quite revealing: 

Effects of element and size on results

The results showed a convergence (in this case) at the 5 deg mesh size. As you would expect the parabolic Tri6 elements performed better than the Tri3, with the crudest Tri3 giving a buckling factor of 20 times that of the finest mesh. It goes to show that you cannot trust your results if your mesh is too coarse.

There was a clue in the course mesh buckling results though: the modes were directly related to the mesh shapes suggesting that the arbitrary mesh was having too much influence. At other times it may not be so obvious.

Buckling of course mesh

 Having established a sensible mesh size I then looked at the effect of the twist of the hyperboloid on the self weight buckling. Note that I didn’t analyse for wind, which is likely to be a dominant load case, just the simpler dead load buckling to examine the effect of the geometry on the stiffness.

Increasing the twist from a tapering cylinder (zero deg twist) did give some reduction in weight and surface area:

Tower weight against twist

The twist gave an initial improvement to the tower’s stiffness, but twisting too much reduces the mid height radius, leading to eventual instability. 

Effect of twist on buckling resistance

What was clear was that making the tower a hyperboloid significantly added stiffness, meaning that there are efficiencies to be found and exploited in your designs.

Conclusion

While string-art pictures generally vanished after having a brief craze in the ‘70s, hyperboloid structures are useful forms to keep in our engineering toolkit: aesthetic, efficient and easy to model in GSA. I know this thanks to my Aunt who bought a Christmas present for her nephew all those years ago.

By Alec Milton

In June 2006, LunchoverIP.com reported 30 countries already had more mobile phones than people. The use of cell phones is especially noticeable in the construction industry, where smartphones are now an essential tool. In addition to the standard functions of calling, texting and emailing, there’s an increase in more sophisticated apps for tasks such as estimating, sourcing materials and viewing drawings.

Smartphones are here to stay, but employees must follow mandated best practices to assure they use them in a way that won’t put the business at risk. Taking security measures to guarantee data cannot be accessed or stolen is important, but a widely overlooked issue with a greater potential of impacting everyday business is email.

Email often is used for time-sensitive exchanges, but it can fall short if the recipient is unavailable or the team is not aware of the communication. It also is used as a written record to be referred to at a later date. However, the unstructured nature of email communication introduces risks. For example, who will know of, or be able to find, project-relevant exchanges if the sender leaves the organization?

Although smartphones are genuine business tools, employees often use company-provided mobile devices for personal communication. Failing to follow company protocol (e.g., forgetting to share an email with the team or keeping a record in a personal email account hidden from colleagues) may simply result in failing to respond in a timely manner. However, failing to meet a deadline or provide evidence when needed can result in huge costs. In the case of Best Buy v. Developer Diversified Realty, the parties argued it would cost in excess of six figures to provide requested email evidence. The judge ignored their pleas and gave them just 28 days to comply. Even Microsoft was ordered to pay $25 million upon failure to provide certain email evidence.

Last March, a lack of documented communication between designers and contractors resulted in a massive installation error at a late stage of a major university project. The settlement, reported to total millions of dollars, was shared by the architect, the MEP engineer and the contractor.

The problem in each case is communication. Solving the problem need not be expensive, but it will prove to be costly if ignored.

“The ability to instantly put your hand on any email not only saves a tremendous amount of time in day-to-day operations, but it also protects you from unfounded litigation. In the construction business, capturing communication is critical to the success of a project and absolutely necessary in order to have full records available for the inevitable disputes that occur in this industry,” says Tony Broomhead, principal and founder of BL Consult. “Too many businesses fail to realize the need for good email filing until it is too late.”

Protecting Against Email Liabilities

1. Put it in writing. Ensure all important communications are in writing and can be tracked. This can be done via email, text messaging or instant messaging depending on if the company’s system allows users to save and file the content.
2. Make it transparent. Ensure communications are recorded somewhere accessible to all relevant parties. Instant messaging is great, but only if a record can be kept of each exchange. When using smartphones for email, make sure users adhere to the company’s filing practices.
3. Structure data. Don’t throw everything in a big bucket. It may provide some peace of mind to have duplicates of every piece of electronic communication in a large unstructured system, but that feeling will evaporate when it’s time to assemble evidence for a trial and someone has to dig through years of data.
4. File project data together. Organizing and filing messages by project will make communications easy to find during the life of the project and post-construction. File emails alongside other project data so all information is in a logical location and accessible to the entire team.
5. Implement an intuitive system. Invest in a system that complements the company’s daily workflow. Don’t adopt systems or procedures that are too difficult for employees to use or they likely will circumvent the system. Implement a “touch it once” philosophy: File outgoing electronic messages when they are sent and file incoming messages once they are read.

When searching for the right system, be cautious of cloud-based solutions. Recent outages that hit RIM’s Blackberry devices and Google Docs underline the need for businesses to manage their own data and not rely on a service provider or third-party technology.

In the construction industry, the need to capture electronic communications and mandate best practices for mobile communications is very important to ensure clarity in project communication and efficiency in execution. The industry is particularly litigious, and companies capable of delivering well-documented evidence in a tight time frame have the immediate advantage in court proceedings.

Lawsuits likely will increase as technology allows more options for undocumented or lost communication. Simple day-to-day operational best practices and a solid system for capturing written communications will do far more for a company in court than the most expensive lawyer.

by Abby Johnson – WebProNews
http://www.oasys-software.com/mailmanager

Popular Mechanics

Catching a flight on time shouldn’t have to be a frustrating crapshoot. Engineers and architects are using new design technologies to envision better ways to get passengers through an airport terminal, and building new terminals like JetBlue’s T5 at New York’s JFK airport to show what the next generation of airports will look like.

by Adam Hadhazy

Read the full article here.

Jet Blue MassMotion Model

Email Still Essential To Business Owners: Survey Says

Is Your Email Server, Serving Your Needs Or Is It Stifling Your Business

So what is in the new version?

Evacuation

We now have evacuation events in MassMotion. What this means is that the agents can be going about their tasks, whether looking for a platform or queuing for processing, but when the evacuation event is activated they all freeze in place before heading for the nearest exit. The pause between their halt and egress is defined by a pre-movement curve, meaning that some will be leaving while others are still working out what to do, or getting in the way depending on where they are.

One thing to watch out for is that as you determine when in the analysis the evacuation event takes place, it is worthwhile stopping the spawning of new agents at that time. If you don’t they will pile-up at the entry portals when they arrive and halt. Similarly, if you are modelling egress from a static start (say an office evacuation) then you are best spawning the agents with the exit links gated and shut so that no one starts to move during the spawning.  When the “alarm goes off”, open the links; the evacuation event will then take over. Alternately spawn the agents with no exit portal defined in their profiles: they will simply stand in place until the evacuation event starts.

As you will not necessarily know where the agents will be when the evacuation event happens, the agents can now be told to go for their nearest exit rather than having to explicitly state where each is to go.

BIM

As Building Information Modelling is becoming more and more common, MassMotion now has an IFC importer. This will recognise standard elements such as floors, stairs, ramps and walls, automatically converting them to MassMotion actors. The options include importing either slabs or rooms from Revit as floors, but be careful if you take both as you may get overlapping floor areas. If you use the rooms option then the Revit doorways will be converted to MassMotion Links between the resulting floors.

Do watch out if your Revit model is a long way from the origin, as MassMotion objects may have trouble validating due to rounding errors when the model extents are dozens of kilometres from the origin.

Simulation

The main change in the MassMotion simulator is the ability to toggle the graphics for the simulation on and off. This allows you to take advantage of the rapid processing without the graphics slowing things down, and then switch them back on to visual checking of the simulation for critical times, and vice versa.

Softimage

MassMotion workbench is now faster at loading models with ICE Actors (i.e. results).

Please note that MassMotion now only supports Softimage 2012, so you will need to upgrade if you are still using 2011.

Conclusion

There you have the improvements to MassMotion in a nutshell. As there is no rest for the wicked we are now starting on version 5.0, but more of that in due course!