Category: Engineering communication
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Wobbling la Passerelle Simone de Beauvoir
[youtube=http://www.youtube.com/watch?v=69NA8E11IDM]
I was invited on Wednesday to go and help wobble the Passerelle Simone de Beauvoir (previous posts here and here). The wobbling was being sollicted in order to conduct ongoing tests on the bridge’s dampers. The tests were being conducted by the CSTB (France’s centre for building science, where I almost ended up doing my projet de fin d’études).
Bridges such as this one, and infamously, London’s Millenium Bridge, are susceptible to wobbling caused by the excitation of one of the bridge’s natural frequencies by the pedestrians who use it. As well as forcing the bridge deck up and down with their footsteps, pedestrians also exert a sideways force as they alternatively plant their left and right feet on the deck. This sideways movement is of a similar frequency to the transverse vibrational mode of lightweight bridges such as this one and the Millenium Bridge. When a bridge does start to shake noticeably, there is a tendency to ‘lock-in’ whereby pedestrians synchronise their steps with the vibration in order to stabilise themselves, but in doing so, give more energy to the vibration. The first time that this lock-in phenomenon was observed was at the opening of the Millenium Bridge.
This sort of vibration is unlikely to cause any damage to the bridge itself but it does make the people onboard feel quite uncomfortable. It is therefore an issue of serviceability. In order to reduce its effects, such bridges are installed with tuned dampers designed specifically to damp out these effects. And in order to check if these dampers are working or not, it takes a group of fifty or so enthusiasts (usually engineers) to jump up and down to see just how much they can get the thing to wobble. I tell you, we got some funny looks from passers by…
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Blog surfing – a make-over for engineers
Interesting comment on Geek Buffet about a make-over for engineers in the States. I have tried to add a British and French take on things.
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Livic at three years old
Livic, the civil engineering newspaper of Imperial College, is now three years old. The fourteenth edition has just been published and I have to say it is the best one yet. With this edition, current editor Andrew Kosinski’s last one of the year, it is clear that it is really starting to achieve the things that I always hoped it would.
Inspired by the student newspapers that I had seen in the States, I stood in 2004 for the CivSoc post of Livic editor. At the time, the paper was but a biannual sheet of A3 paper stuck on the department wall, nothing more. (The name Livic comes from Civil spelled backwards – a previous incarnation had apparently been called ‘Concrete’ – catchy huh?) My hope was to turn Livic into a regular student newspaper much like those that I had seen abroad. Kosinski has been onboard since the beginning, realising on paper what had previously only been an idea.
I had several goals in mind when starting out. The first was to encourage student writing. It had struck me that there were precious few creative outlets at Imperial and so I hoped to add at least one to that impovrished list. The second was to encourage staff contributions, and in doing so, improve communication within the department. I had the impression at the time that there was little awareness of the research that went on in the department, and I thought that Livic could help. Finally, a slick looking paper with a broad readership, it was hoped, would attract advertising from industry which might at the very least have paid for printing, and more ambitiously, go a little way towards boosting CivSoc’s budget.
In that first year, we made some progress towards reaching those goals. For starters, some forty students contributed articles on a wide range of subjects. What was difficult was trying to get reporters to write articles that went into any depth. I seem to remember there being some staff writing, but calls for articles often went unheard, or weren’t followed up. We did manage to break a couple of important departmental news stories (the Creative Resign article being one memorable example), but these were by no means exclusives.
By comparison, the Livic of today has come a long way. The articles are much more in depth and they cover a wide range of topics. An important story about the future of the course is on the front page and inside there are staff contributions as well a revealing interview with a lecturer. All in all it is cracking read! It is also interesting to see how the layout has changed with time. It keeps getting slicker. I am certain the Arup were more than happy to place an advert I such a classy publication.
When I was editor, sure I had ideas, but I didn’t have the first clue about how to realise them on paper. Luckily there was Kosinski who did. Both the subsequent editors, Alex Morris last year and Kosinski this year, have not only had the ideas but have also had the skills necessary to assemble the paper on the screen. And I think it is these two skills combined with a desire to say something and knowing how to say it, that are now pre-requisites of a Livic editor, a role which three years ago was somewhat of a joke position on the committee.
And so what of the future? As of next year, the first three editors will all have left the department. There is always the fear that one day Livic will fizzle out for lack of enthusiasm, and it does take enthusiasm to get something like this out of the door. But with fourteen issues in the bag, Livic has now got momentum. Elections have just been held for the post of next year’s editor. I wish him or her luck and I look forward to seeing Livic’s continuing evolution.
Access Livic online here.
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Pounds per square inch?? (project update)
Today I started getting into the nitty gritty of how to stop a floor from vibrating. When dimensioning the floor slab of a building, one of the considerations is to check whether the natural frequency of the floor is in the same frequency range as that for footsteps. If the two frequencies do coincide the latter could resonate with the first causing the floor to shake.
Today I have been looking at an American document that brings together the different ways of estimation this interaction. Most of the results are based on empirical evidence of what seems to work. This lack of rigour is fine with me, and is common in engineering. The thing which has really held me up is the units: all the calculations are in pounds, feet and inches! Could there be a more unhelpful system of measurement?
Curious about this archaic standard, I started hunting around on Wikipdedia and found a wealth of information on the origins of both systems. Apparently, the only countries still to use imperial units of measurement are the USA, Liberia and Myanmar, although, I might add that here in the office my colleagues were surprised to here that in the UK we also use the metric system.
I urge anyone who is similarly disposed towards the imperial system, to use this site to help them out.
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Bending beams and counting the cost
During these first few weeks of my placement I have been carrying out some fairly entry-level calculations on a forty-five storey tower. These follow on nicely from courses in concrete and steel design that I took during my first term at ENPC. However, while these courses were based on the new Eurocode regulations (currently being adopted in the U.K. and in France), the company I am working for is in a transition period during which it is using the new code for some projects and the old French code for others.
During the first few days I therefore had to get my head round these older regulations that I had never seen before. In particular I was getting hung up on the issue of how much a beam should bend in service. While a bending beam may not necessarily break, it may cause temporary walls to crack and finishes to become damaged: hence the limits on how far a beam can deflect in everyday use. Both codes have similar limits for this deflection; the only difference is in how you calculate the deflection. The Eurocode is a lot more flexible (read vague) on how to perform this sort calculation than the French code. I spent a long time going into the detail of how to apply the French code and got quite confused. Everyone that I asked had their own way of doing it but no one seemed to have a definitive answer (this was not helped by the fact that those who do know are rushed off their feet). In the end, I found that these technicalities accounted for minor differences and I was able to move on. I remain unsatisfied however with my methodology.
Once a methodology is established, calculations can be automated with Excel. Everyone has their own Excel sheets to speed things up. Or at least that is the idea. When the sheet is up and running, it is very easy to rattle off calculations, but getting it to work is the difficult part and I sometimes wonder whether the time taken verifying the code doesn’t add up to more than it would have taken to do the calculations by hand. It is also very difficult to follow your working in Excel, and even harder to follow someone else’s. The biggest challenge is making these automated calculations readable to others.
As well as the program for dimensioning beams, I am now on the second version of a program that will work out an approximate cost for this tower. Something that started relatively simply has spiralled out of control, hence the second version. I hope to be able to report progress tomorrow!
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Film uploaded to my new website
Check out my new website where I have posted a couple of movie clips. The first is a documentary that readers of this blog may remember I made back at the start of my semester at ENPC. I had been asked to give a presentation as part of a language class on any topic that of relevance to engineering. Weary of Power Point, I decided instead to make a short film that I then presented to the class. Those who have studied under the French system will spot the strategic use of ‘articulateurs’. I would only like to add that I hope my French has improved somewhat since those heady first weeks of term.
The other clip I made using some panoramic photos that I took at the top of the ‘Gherkin’ in 2004. I found a programme that would string them all together. I then used imovie to make the photo pan and uploaded that mpeg to the web. This process was a bit laborious. Can anyone advise me if it would have been quicker to create a photocast instead?
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Blog from beyond the grave
The Institution of Civil Engineers, in celebration of the 250th anniversary of the birthThomas Telford, has launched a blog in the name of that great Scottish engineer. The blog will contain extracts from diary entries and letters by Telford, the ICE’s first president. I have to confess that though Telford is credited with thousands of structures, a great number of which remain standing, I do not know enough about him. I hope that this blog will help me fill some gaps!
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Meet Mr Alphand
When Haussmann was busy tearing down and rebuilding large swathes of Paris, he wasn’t doing it all by himself. His chief engineer was this fellow, M Alphand. In this portrait by Alfred Roll, he is standing on the building site of the Petit Palais in 1888. Appropriately, it is now hanging in pride of place in the Petit Palais. As far as our history of art lecturer is aware, it is in the only portrait of an engineer in Paris.
The Petit Palais is an interesting place, although not as immediately so from a structural point of view as its glass-domed big brother opposite, the Grand Palais. This mock classical building has frescoes on its ceiling that, first time round, failed to draw my attention. On a second lap however, I was invited to take a closer look at these paintings. Sure, there were the cherubs floating around, but the clouds in which they were flying were not in fact clouds, but smoke rising from factories in one corner, and a steam train in the other. Progress!
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It is nearly always a lovely day in Architecture world
This quote is from Jonathan Glancey in today’s G2:
“It is nearly always a lovely day in Architecture World. Happy, shiny, gym-fit young people living today’s latte-fuelled urban 24-hour lifestyle, stride through sparkling, quango-approved “regeneration” utopias. In these illustrations it never rains. The wind never blows. Snow is an alien concept.” Lamenting the fact that so many architectural renderings of future developments look blandly sunny, he rightly points out that many drawings are done with the same standard bits of software so every scheme looks much of a muchness.Structural engineers on the other hand could do with a little more sunny weather. While the architects are worrying about what the building will look like in the sunshine, engineers are more bothered about whether it will stand up in the wind. Those who are (un)lucky enough not to know about these things may like to know that a significant portion of a building’s structure is there to stop it falling over in the wind. And once the wind is catered for, the weight of a dusting of snow on the roof – by no means insignificant – has to be accomodated. And of course there is rain water to look out for, collecting under joints in steel and causing rust in hidden places, getting into cracks in the concrete and coroding the rebar or just making stuff rot. When all this is said, I quite like the sound of Architecture World.
On the subject of gym-fit people walking through these shiny utopias, I am often interested by the care that goes into choosing the people that architects put into their drawings. The people in a landscape drawing I was working from for a gallery were wearing the most skin-tight jeans (These architects were obviously certain that this project would be finished before next year by which time drain pipes will habe bewly returned to fashion’s gutter). I can imagine the meetings where architects sit around a table and work out how the people in their drawings can best represent the desing ethos of the company. I imagine Richard Rogers (Pompidou centre and Lloyds of London) proposing that the people they use have all their veins and digestive systems on the outside! On a more serious note, I do know of a project where the architects were asked by the client to remove two people from their drawings because they looked too homosexual. Doesn’t sound all that utopian to me.