If nobody has mentioned the Tacoma Narrows bridge yet ... . A fine early experience of resonance and the problems with cable stayed bridges. Best of all, despite the fantastic film footage, nobody was killed in the breaking of this bridge. Several people would have thought they were candidates. This is by far the best film footage of the event that i have ever seen - well worth watching. Sound track is execrable. Can't have everything :-). http://www.youtube.com/watch?v=j-zczJXSxnw This may have been "post processed" and possibly colorised. This is more like what is usually seen. Has better footage of the actual moment of collapse. http://www.youtube.com/watch?v=HxTZ446tbzE&feature=related Script identical in most cases. Prof xxx is brave beyond belief (but, see below). Two men seen at end of footage MUST be engineers ;-). This version provides other color footage. it also says the dog rescue story is untrue and that the dog died. http://www.youtube.com/watch?v=vu4LPTsy_xY&feature=related _________________________ The london Millenium pedestrian only bridge suffered from a subtler fatal flaw which was discovered soon after it opened. It was closed again soon after and took AFAIR about 2 years to sort out. The second stage of the problem is resonance if people walk in step - the designers were well aware of this and didn't see it as a problem. BUT, The first stage of the problem was an effect discovered many decades earlier and then largely forgotten - if a bridge with a natural oscillatory frequency is excited by random input (lots of pedestrians) it can produce a forcing signal that is not large enough to be damaging to the structure BUT which drives the exciters towards the resonance point. ie the walkers resond to the bridghe's movements by altering thei stride and gait somewhat and are driven into resonance with the bridge so that THEN they drive the resonance more solidly. The MB had substantial dampers fitted which preventthis - they are visible in photos if you know that there is something tgere to look for. _______________ Anti-resoant dampers for use in de-swaying tall buildings were mentioned. Taipei 101was at one time the tallest building in the world by AFAIR 5 of the 6 metrics used to measure building height as agreed to by the tall building builders association (names have been mutilated due to imperfect memory, facts approx correct). One floor below the viewing deck there is a large and very heavy and very high tech suspended weight - approximately stepped spherical. Ah well ... Gargoyle says ... http://en.wikipedia.org/wiki/Taipei_101 http://www.popularmechanics.com/technology/industry/1612252.html World's tallest at May 2005 (I was there ???) Burj Dubai is now taller BUT will not officially meet the definition of a "building" until later this year (fwiw). 1667 ft. 660 ft. from a major fault line in Taiwan, ... could be subjected to earthquakes, typhoons and fierce winds ... 730-ton tuned mass damper (TMD). It acts like a giant pendulum to counteract the building's movement--reducing sway due to wind by 30 to 40 percent. Constructed by specialty engineering firm Motioneering, the damper was too heavy to be lifted by crane and had to be assembled on-site. Eight steel cables form a sling to support the ball, while eight viscous dampers act like shock absorbers when the sphere shifts. Able to move 5 ft. in any direction, the Taipei TMD is the world's largest and heaviest. This gold-colored orb is on view from restaurants, bars and observation decks between the 88th and 92nd stories. A bumper ring prevents the ball from swaying too far, should that much swaying ever need to occur. Our recommendation, in that case, would be an immediate egress to firmer ground. 2009/7/5 Carl Denk > Oh, yes, it's the resonance frequency and the frequency of whatever, > like horses or other things in unison. Think of a child on a playground > swing. At the right time a small push and the amplitude is greater if > that push is right after the extreme limit of travel. If the push is > just before the limit, amplitude is reduced. > > John Gardner wrote: > > 20-odd hoss & riders that different from 10-ton truck? > > > > Jack > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist