На двух опорах. С ним произошла интересная история. Открыли его в рамках празднования 2000 года (он так и называется - Millennium Bridge), но как только на него вошли люди, oн вдруг вошёл в сильный резонанс из-за своеобразной положительной обратной связи: небольшие раскачивания моста усиливались качающимися людьми. И мост закрыли на переделку почти на два года. Вот что пишет Википедия (http://en.wikipedia.org/wiki/Millennium_Bridge_(London)):
The bridge's movements were caused by a 'positive feedback' phenomenon, known as Synchronous Lateral Excitation. The natural sway motion of people walking caused small sideways oscillations in the bridge, which in turn caused people on the bridge to sway in step, increasing the amplitude of the bridge oscillations and continually reinforcing the effect.
Resonant vibrational modes due to vertical loads (such as trains, traffic, pedestrians) and wind loads are well understood in bridge design. In the case of the Millennium Bridge, because the lateral motion caused the pedestrians loading the bridge to directly participate with the bridge, the vibrational modes had not been anticipated by the designers.
After extensive analysis by the engineers, the problem was fixed by the retrofitting of 37 fluid-viscous dampers (energy dissipating) to control horizontal movement and 52 tuned mass dampers (inertial) to control vertical movement. This took from May 2001 to January 2002 and cost £5m. After a period of testing, the bridge was successfully re-opened on 22 February 2002. The bridge has not been subject to significant vibration since.
Появились в середине 50-х (начало вещания в NTSC - 1953 или 1954 год), но широко распространились только к концу 60-х. Кстати, смешно, что цифровой стандарт телевизионного вещания в Северной Америке называется ATSC. Если учесть, что злые люди расшифровывали NTSC как Never The Same Color :)
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The bridge's movements were caused by a 'positive feedback' phenomenon, known as Synchronous Lateral Excitation. The natural sway motion of people walking caused small sideways oscillations in the bridge, which in turn caused people on the bridge to sway in step, increasing the amplitude of the bridge oscillations and continually reinforcing the effect.
Resonant vibrational modes due to vertical loads (such as trains, traffic, pedestrians) and wind loads are well understood in bridge design. In the case of the Millennium Bridge, because the lateral motion caused the pedestrians loading the bridge to directly participate with the bridge, the vibrational modes had not been anticipated by the designers.
After extensive analysis by the engineers, the problem was fixed by the retrofitting of 37 fluid-viscous dampers (energy dissipating) to control horizontal movement and 52 tuned mass dampers (inertial) to control vertical movement. This took from May 2001 to January 2002 and cost £5m. After a period of testing, the bridge was successfully re-opened on 22 February 2002. The bridge has not been subject to significant vibration since.
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