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Engineers Should Consider Human Induced Vibrations – Here’s Why:

Last Updated on March 19, 2020 by Admin

Whenever the term ‘human-induced vibration’ is mentioned, perhaps you envisage the Millennium Bridge swaying?  Thankfully, these vibrations – caused by, for example, people walking – will not cause significant harm, but they are very important to think about when thinking about designing and creating structures, like buildings or bridges. Read this article to know about why engineers should consider human induced vibrations?

Different Types of Vibrations

There are two types of vibrations, one is called resonance and the other type is called aeroelastic fluttering.

Did you know resonance is a type of vibration which occurs when one object vibrates at the same natural frequency as the other? The second object resonates with this and begins to vibrate too.

Think singing to break a wine glass! Although the person singing isn’t touching the glass, the vibrations of their voice are resonating with the glass’s natural frequency, causing this vibration to get stronger and stronger and eventually, break the glass.

Aeroelastic flutter is quite similar. When force is applied to an object, it shakes. It’s not necessarily at the same frequency as the object’s natural vibration, but it makes the object move all the same.

Objects that resonate also flutters. But not everything that flutters is resonating. This is how confusion over disasters such as the Tacoma Bridge collapse occurs — for a long time, and to this day, the event is used as a textbook example of resonance. However, it’s been argued that the bridge’s collapse wasn’t caused by resonance, but by fluttering.

From human-induced vibrations, force is applied which then causes the building or structure to vibrate, which is known as fluttering. Some instances would also see resonation happening too, but it wouldn’t be a certainty. Engineers must, of course, design to reduce the damage or discomfort caused by either fluttering or resonating.

What are the impacts from human-induced vibration?

The effects of these vibrations include:

  • Damaging sensitive equipment. Depending on the building’s purpose, what it houses can be affected by the vibrations of people using the building. Universities, for example, may have sensitive equipment whose accuracy and performance could be damaged by vibrations.
  • Rocking bridges. One of the most famous examples of resonance, human-induced vibrations, and fluttering all impacting a structure occurred with the Millennium Bridge. As people walked across the bridge, the vibrations and swaying caused oscillations in the bridge. Everyone crossing the bridge would then sway at the same time to avoid falling over, resulting in a cycle of increasing and amplifying the swaying effect.
  • Human health distress. According to research, vibrations in buildings and structures can cause depression and even motion sickness in inhabitants. Buildings naturally respond to external factors such as the wind or human footfall within. This low-frequency vibration can be felt, even subconsciously, by people. It has been argued that modern designs featuring thinner floor slabs and wider spacing in column design mean that these new builds are not as effective at dampening vibrations as older buildings are.
  • Endangering the integrity of a structure. The build-up of constant vibrations on a structure can, eventually, lead to structural integrity being compromised. A worst-case scenario would be the complete collapse of said structure.

Avoiding it

These days, newer designs use thinner slabs and wider columns compared to older designs, so these structures tend to vibrate. Using structural design software at the design stage is an effective method for engineers to test footfall on design and see the resulting vibrations.

Engineers should always consider creating solutions to stop the effects of vibrations in buildings becoming unsafe and uncomfortable.

Sources

https://www.oasys-software.com/news/analysing-vibration-with-gsa/
https://www.oasys-software.com/case-studies/footfall-analysis-singapores-helix-bridge/
https://www.oasys-software.com/case-studies/princeton-university-frick-laboratory/
http://homepage.tudelft.nl/p3r3s/MSc_projects/reportRoos.pdf
https://www.forbes.com/sites/startswithabang/2017/05/24/science-busts-the-biggest-myth-ever-about-why-bridges-collapse/#1b9e3b001f4c
https://phys.org/news/2017-03-impact-bridges-skyscrapers-human-health.html
https://phys.org/news/2017-03-impact-bridges-skyscrapers-human-health.html
https://www.quora.com/Whats-the-difference-between-resonance-and-aeroelastic-flutter
https://www.telegraph.co.uk/science/2017/03/19/wobbly-skyscrapers-may-trigger-motion-sickness-depression-warn/

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