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    Why it’s Important to Reduce the Effects of Human-induced Vibrations in Engineering

    Human induced vibration is when footfall causes vibrations
    in structures. This might sound dangerous to a structure’s integrity, but the
    effects from human induced vibrations are more likely to cause discomfort in
    people rather than ruin the design. It’s important for engineers to make their
    structures secure and comfortable for people to pass through, so in this
    article we’ll explore what can actually happen from these vibrations.

    Resonance and Fluttering Vibrations

    Two of the main effects of vibrations on structures are
    resonance and aeroelastic fluttering.

    Resonance vibrations happen when two objects vibrate at the
    same natural frequency as each other. 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.

    However, aeroelastic flutter is slightly different. A force
    is applied to an object, which causes it to shake. It’s not necessarily at the
    same frequency as the object’s natural vibration, but it makes the object move
    all the same.

    When an object resonates, it flutters too. 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.

    Human induced vibrations are categorised as fluttering
    because human movement is applying force which causes the structure to vibrate.
    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. 

    Human-induced Vibrations Effects

    Human induced vibration can lead to several affects upon the
    structure and its users. These include:

    • Having damaging effects on 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.
    • Causing bridges to sway. 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.
    • Causing human heath to suffer. 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. 
    • Threatening structural integrity. The
      build-up of constant vibrations on a structure can, eventually, lead to
      structural integrity being compromised. A worse-case scenario would be the
      complete collapse of said structure.

    Reducing the Effects

    Unlike older designs, modern designs have an affinity for
    thinner slabs and wider column spacing, which makes them prone 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.

    Vibrations are always going to happen, so it’s important for
    engineers to make sure the effects are reduced as much as possible.

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