By Amy Hodgetts, content writer on behalf of Oasys Software
Human induced vibration, or more accurately vibrations caused by human footfall, often conjures images of Millennium Bridge style swaying or collapsing buildings. But in reality, the ‘damage’ caused by human induced vibrations is less likely to ruin a structure and more likely to cause discomfort in people.
Though not as dramatic as a structural failure, any good engineer wants to make sure the people using their structures, be it bridges or buildings or anything in between, can do so safely and comfortably. This is why human induced vibration must be considered within the design process.
There are two ways that human-induced vibrations affect structures: resonant, and impulse or transient response. Put simply, resonance occurs when Object A vibrates at the same natural frequency as Object B. Object B 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. In the case of a structure, resonance occurs when the pedestrian’s feet land in time with the vibration.
On the other hand, impulse or transient vibration responses can be a problem on structures where its natural frequencies are too high for resonance to occur, such as where the structure is light or stiff. Here the discomfort is caused by the initial ‘bounce’ of the structure caused by the footstep and is a concern on light or stiff structures.
Engineers must, of course, design to reduce the vibration effects caused by either impulse or resonance. Human induced vibration can lead to a number of effects upon the structure and its users. These include:
As mentioned, modern designs that favour thinner slabs and wider column spacing are particularly susceptible to all forms of vibration, human induced or otherwise, but short spans can also suffer due to their low mass. Using sophisticated structural analysis software is an effective method for engineers to test for and mitigate footfall and other vibrations at the design stage.
Having joined the magazine in 2012, Claire developed her knowledge of the industry through the numerous company visits, exhibitions and conferences she attended both in the UK and abroad.
Claire prides herself on keeping readers well informed and up to date with the latest industry news.