A natural occurrence of someone walking is human induced vibrations. The effects of these vibrations aren’t life and death but can impact structures in a variety of ways, whether they’re buildings or bridges. Although not as serious as structural failure, minimising vibrations is a part of design that engineers need to largely consider in order to make people feel safe and comfortable. In this article, we’ll look at the impacts of vibrations.
The two main effects of human induced vibrations are resonance and aeroelastic fluttering.
In simpler terms, resonance happens when Object X vibrates at the same frequency as Object Y’s natural frequency. Object Y 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 happens when a force is exerted to an object which in turn makes it shake. It’s not necessarily at the same frequency as Object B’s natural vibration, but it makes Object B move all the same.
When something resonates, it also flutters. But not everything that flutters is necessarily resonating. This is how confusion over disasters such as the Tacoma Bridge collapse occur — 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.
When human force is exerted and causes an object to vibrate, this is 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.
Vibrations from human footfall, and the fluttering or resonation it can cause, can have many effects on a structure. These include:
Compared to old designs, contemporary structures tend to integrate thinner slabs and columns that are spaced widely, making them vulnerable to vibrations. Using structural design software at the design stage is an effective method for engineers to test footfall on a design and see the resulting vibrations.
Although vibrations are something that happen naturally, engineers must consider reducing the effects of them in their designs to ensure security and comfort.
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://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