Research, Technology

Suspension bridges turned out to be more dangerous than previously thought

At the moment, the longest suspension bridge inthe world is considered the crossing of the Portuguese Paiva River. Its construction was completed in May 2021 - the length of the bridge was 516 meters and it takes up to 10 minutes to pass through it. True, few dare to walk along this crossing, because due to the steps of a large number of people, the bridge strongly sways to the sides and there is a danger of falling. However, this problem is relevant even for the huge Brooklyn Bridge and many other similar structures. Until now, it was believed that bridges begin to wobble dangerously due to the synchronized movement of people - when they walk side by side, a pendulum effect occurs. However, in a recent study, scientists found that bridges are more dangerous structures and loosen even if people are not walking in sync.

Suspension bridge over the Portuguese river Paiva

Interesting fact: in 2022 the record for the longest bridge in the worldwill be beaten. In the Czech region of Moravia, the construction of a crossing from the Slamnik ridge to the Chlum ridge has begun. The 721 meter long bridge will be supported by cables more than 7 centimeters thick.

Why do bridges stagger when walking?

The new reason for the swaying of bridges wasdescribed in the scientific publication Science Alert. Once again, it is worth emphasizing that the results obtained do not disprove the fact that bridges swing due to the pendulum effect caused by the synchronized walking of people. The data obtained only expands the knowledge of scientists about this phenomenon. During the course of the study, it became clear that walking on long and unstable bridges is dangerous even if the steps of the people do not match.

Not every person dares to walk on suspension bridges and there are reasons for this.

As part of their scientific work, scientists have studied various cases of dangerous swinging of bridges. In some cases, all the pedestrians walked in sync, while in others - each with his own step.

Danger of suspension bridges

One of the most striking examples of extremethe swinging bridge is an incident that occurred in 2000. London Millennium Bridge opened in June this year, but early visitors were concerned that it wobbled when walking. In this regard, the bridge was closed for two days, and then for a couple of years altogether - it had to be strengthened. The bridge was eventually reopened in February 2002.

London Millennium Bridge

Another incident happened in 2003.Then on the East Coast of the United States there was a power outage and many people had to walk across the Brooklyn Bridge, which connects New York and Manhattan. Due to the numerous steps, he began to shake badly and people even reported dizziness and inability to maintain dizziness.

People on the Brooklyn Bridge in 2003

After examining the details of these cases, scientists cameto the conclusion that even with asynchronous walking, people swing the structure strongly. This is due to the fact that each of them is trying to maintain balance and by their efforts further increase the effect of the pendulum. According to the authors of the scientific work, this is a great example of negative damping, where weak vibrations cause a much greater end result than strong ones. In the case of the Millennium Bridge, 165 people had enough movement to swing the structure. If the bridge is smaller, even fewer people are enough to break its stability.

See also: Humanity has changed the land beyond recognition. But what about water?

Suspension bridge collapses

Suspension bridge collapses are far fromrarity. One of these cases occurred in 2016 in Indonesia. Too many people were passing across the bridge between Nusa Lembongan and Nusa Cheningan during the ceremony. Due to the heavy weight (and, most likely, vibration of the structure), one of the cables burst and people fell into the water. As a result of this terrible incident, about 34 people were injured.

Collapse of the bridge between the islands of Nusa Lembongan and Nusa Cheningan

Three years later, another accidenthappened in China, but in this case, the reason was the banal stupidity of the people. In the video, one person crossing a river in Guangdong province can be seen swinging a bridge held on ropes. It goes without saying that the structure could not stand it and people fell into the water. And there are a lot of such cases - news about them appears several times a year.

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There are a huge number of bridges in the world andthey differ both in appearance and in purpose. On our site there is an article about the ten longest bridges in the world - I highly recommend reading it. Here is the link.