Now This Really Does Take The Biscuit!

First, there\’s the standard engineer\’s fallacy:

Before asking how many engineers we need, we should first ask: "What will they be doing?"

We should not even be asking how many engineers we need. We should ask "do we have a functioning market for engineers? Do people respond to the incentives within that market?" If the answer to both is "Yes" then we have the number of engineers that we need.

But much more fun that that:

Chris Wise, the engineering director behind London\’s Millennium bridge

We\’re now taking advice on engineering from th bloke behind the Millennium Bridge? The one that ignored the basics of harmonics? Even after the Tacoma Narrows bridge, the film of which is shown in about the first 15 minutes of any engineering course?

was professor of creative design at Imperial College until 2005

Those who can do, those who can\’t teach, eh?

14 comments on “Now This Really Does Take The Biscuit!

  1. You could make facinating hay with the fact that engineers get excellent wages outside of engineering. But my favourite anecdote was from the mid 90’s, when the head of British Aerospace declared he couldn’t find enough British engineers to staff his operation and that he would have to start recruiting American’s and German’s instead.

    The previous week, I had noted an advertisement in Flight International magazine for weapon systems engineers with three years experience. The starting salary was 16.5K , which was approximately the average graduate starting salary at the time…

    Rupert (B Eng Mech)

  2. “The one that ignored the basics of harmonics? Even after the Tacoma Narrows bridge, the film of which is shown in about the first 15 minutes of any engineering course?”

    No, it didn’t Tim. It wasn’t a classic harmonics problem: it was a bio-feedback problem. In fact, after Arup’s research it is now called “Synchronous Lateral Excitation” in the industry.

    Tim, I have a lot of respect for you as a blogger, but shooting off critical pieces with no expertise or research (and an ad hominem attack, for that matter) lowers you to the level of an MSM journalist, the very thing that people read blogs to sidestep.

  3. So although bodies of soldiers have been ordered to break step when crossing a temporary bridge since time immemorial only since Arup researched the phenomenon is a wobbly bridge due to Synchronous Lateral Excitation and bio-feedback. My admiration for Civil Engineers’ ability to turn common sense into a mathematical equation grows every day. Is it still true that more is spent annually by the construction industry on litigation than research?

  4. As Kay Tie says, it wasn’t expected that people would walk in step like that.

    With hindsight we can see that they might, but it was assumed that people don’t by everyone until it was discovered to be false…

  5. Whatever the phenomenon is called, Tim’s point that it had been seen before still stands, and the fact that the engineer might have been aware of it, but felt it wouldn’t be a factor because of assumed human behaviour doesn’t mean it wasn’t a failing of engineering, which is about making assumptions that accord well with reality.

    The fact that engineers are paid better outside engineering just means that engineering as an activity is not as highly valued in the market as other activities. If engineering grads can get salaries in the City 3 times higher than they can get working as engineers, it must be because the City can use them to make more money. Which is better for everyone, right?

  6. I think the Devil’s Kitchen has a nice piece about Camelot, dumb bint Tina Farrell of Levenshulme, who “isn’t having it” when told -6 is higher than -8, and the consequences of the “cult of esteem”. Well sorry, but it goes beyond chavs – intelligent people here have way too much self-esteem…

    “So although bodies of soldiers have been ordered to break step when crossing a temporary bridge since time immemorial only since Arup researched the phenomenon is a wobbly bridge due to Synchronous Lateral Excitation and bio-feedback.”

    No, Brian, you know a bit, but too little. Go and read about it. No, really, go and find out rather than shoot your mouth off. As a hint in directing your research, focus on the word LATERAL. Soldiers marching tend not to do so LATERALLY.

    “Tim’s point that it had been seen before still stands”

    The particular issue with the Millennium Bridge was that when swaying sideways at a particular frequency, individual people tend to instinctively walk like on a rolling deck of a ship, that they can synchronise the walking, and that for a lightweight bridge with a lot of people on it, this can amplify the oscillations. Where had this been seen before and entered the literature of the profession?

  7. “Where had this been seen before and entered the literature of the profession?” Dunno, but I have vague memories of fairground fun that worked on that principle. And a clear memory of a childrens’ playground suspension bridge that led to lots of shrieking and LATERAL movement. Mathematical modelling is a dangerous game if you don’t know what you’re talking about (see Global Warmongers, for example, or Financial Derivative modellers.)

  8. Is Kay Tie an engineer? Apparently not a very civil one. I was only making the point that things may be discovered several times before being generally accepted. I stand chastened and corrected because any movement will bring the bridge down.

  9. If only Kay Tie knew I had already read Linking London: The Millenium Bridge he/she might have appreciated that I had read paragraphs 3.1 and 4.13 and not shot his/her mouth off at me.

  10. Yes, what a perfect world we would inhabit if only people saw sense and got economists to design bridges!

  11. “Synchronous Lateral Excitation” is a phenomenon that anyone who has ever knocked up a bridge with some planks & rope discovers as soon as they start to use it. “Synchronous Lateral Excitation” is also something you ‘discover’ when you’re paid a great deal of money to design a show-piece bridge and forget or more likely never have the hands on experience of doing the above. “Synchronous Lateral Excitation” can be used to describe the process of explaining an obvious & expensive f**k-up to the people who paid for it, although to those more straightforward the verb “w*nking” seems equally appropriate

  12. Regardless of whether Synchronous Lateral Excitation had been observed before, the finite element model of the bridge should have shown that its natural frequency was dangerously close to the frequency of steps in a normal human’s walking speed. The bridge should have been designed to keep the two well apart.

  13. Mr Newman
    To be fair I don’t think SLR is strictly a result of frequency. It’s what happens when the mass of the people using the structure is a high proportion of the mass of the structure itself. When the bridge starts to swing the natural tendency is for the users to move away from the side that is lowest. Unfortunately that means that they generally arrive at the upside at the point when the oscillation is reversing so accelerating the motion. It’s similar to pumping a child’s swing. It’s different because the dynamics of the situation tend to actually make the movements of the occupants coincide with the frequency of the oscillation. ie the faster the thing swings the quicker you try and get from the lower side to the upper.
    There’s much the same thing happening when two people try and trade places in a small boat. One person standing up can compensate for the rocking of the boat by adjusting their stance to dampen the motion. When two try to do the same thing simultaneously it’s very easy to overcompensate, amplifying the rocking and then they both get wet.
    When building suspension bridges ‘in the wild’ using simple materials one usually tries to get the suspension ropes as high as possible. Between a couple of convenient trees is favourite. Then hang the walkway underneath it. That way when it swings – which it will – the walkway stays reasonably level and gravity keeps it from catastrophic oscillation. The sort of rope bridges favoured in jungle adventure films and which are much closer in concept to sunshine’s Thames crossing, are a nightmare to cross. They behave rather like a skipping rope held between two uncoordinated schoolgirls. They wriggle, they swing and in a worst case the centre can swing right over the top until it’s inverted.
    Crap design

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