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Notes from Tony's desk Random thoughts from Tony Bryer

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Old 20th March 2011, 11:02 AM   #1
Tony Bryer
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Default If it looks wrong .....

.... it probably is.

A current story on the Daily Mail website http://www.dailymail.co.uk/news/arti...hi-habour.html is headed The 175,000-tonne ship lifted up and dumped on the harbour-side like a bit of driftwood by Japanese tsunami. If you know anything about ships (I know just a little) you'd know that modern large cruise ships are typically 70-90,000 tons - the mega-liner Queen Mary 2 is 151,400 tons. So if the headline was true, this would be one enormous ship; it isn't. A few seconds on Google revealed the actual size of this ship, Asia Symphony, is 6,175 tons! Someone should have spotted this before the story was published.

Relevance here: you need to look over your calculations and ask yourself whether what they show looks right. Let me assure you that a 127x76 UB will not span a 10m opening whatever the printout says, and if one of our programs suggests a 406x174 over a 2.3m through room opening, something isn't right.
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Old 19th May 2011, 01:57 PM   #2
HarryR
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Default Re: If it looks wrong .....

If it looks right it probably is but you've got to get to the stage of knowing what looks right (or wrong) first! An embarrassing time for my previous employer (v. well-known but must remain unnamed) when a steel detail, 10's of which already fabricated, was found to be wrong by a checking Engineer despite having looked pretty good to start with. The problem (not mine, fortunately) came down to no one except the checking Engineer thinking about prying forces in a 3-dimensional cable spider connection. You've got to think from basics all the time (and don't have anything fabricated before someone with a brain has checked it). The point is that it looked right but the calculations were out by just enough to give a real possibility of failure.
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Old 23rd May 2011, 01:17 AM   #3
Tony Bryer
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Default Re: If it looks wrong .....

Thanks for the comment, Harry. Yes, a sense of what is right only comes with experience. The danger today is that too many people have blind faith in what comes out of a computer and don't appreciate the need for sound engineering judgement - witness recent comments in the Structural Engineer's Verulam column. They say that all publicity is good publicity but I'd rather not be reading about SuperBeam-produced calcs submitted by people who apparently just don't have a proper understanding of the subject.

The other thing you allude to, just as much a problem in pre-computer days, is that when you're checking calcs (your own or other people's) it's very easy to get totally absorbed in what is in front of you, and fail to step back and see whether anything is missing. The selected 203x133x30 UB may be fine, but what holds it up?
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