May 16, 2020

COVID-19: UK construction sites to 'open on evenings and weekends'

Dan Weatherley
2 min
COVID-19: UK construction sites to 'open on evenings and weekends'
Ministers in the United Kingdom are planning to change the law, overriding current restrictions to kickstart the country’s economy following coronavir...

Ministers in the United Kingdom are planning to change the law, overriding current restrictions to kickstart the country’s economy following coronavirus lockdown.

The coronavirus pandemic has begun to have a considerable impact on the UK’s economy thanks to industries such as construction and manufacturing slowing or, in many cases, completely halting operations. Countless construction sites across Britain have closed temporarily to help slow the spread of COVID-19, despite there not being a legal requirement to completely close sites.

In the UK, a law is currently in place which protects Construction sites’ local environment from potential noise pollution between the hours of 6pm and 8am Monday to Friday, and Saturdays between 1pm and 8am. Noisy work carried out on such sites any time on a Sunday or bank holiday is illegal in the country.

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These laws are set to temporarily change as part of the first stages of re-opening the nation’s economy whilst attempting to prevent small building firms from being struck hard, in addition to giving companies time to “catch up” on work as their staff begin to return to site post-lockdown.

Other countries across Europe have also started announcing similar measures to restart the construction industry. In Italy, public construction projects are able to begin today. Furthermore, Spain announced around a fortnight ago that employees in manufacturing, construction, and some services were also able to return to work but must adhere to strict coronavirus guidelines and social distancing measures.

It is expected that the construction industry across the UK, Europe and beyond will feel the pinch for a number of months and potentially even longer for some firms as lockdowns across numerous countries continue at full effect, with only some countries now gradually starting to reduce some of the measures and policies put in place.

Take a look at Google’s COVID-19 Information & Resources page for the latest information on the disease in your nation.

 

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Jun 17, 2021

Why engineers must always consider human-induced vibration

Vibrations
Engineering
design
Structuralintegrity
Dominic Ellis
3 min
Human-induced vibration can lead to a number of effects upon the structure and its users

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.

Resonance v Impulse

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 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.

Potential impacts from human induced vibration

Human induced vibration can lead to a number of effects upon the structure and its users. These include:

  • Interfering with sensitive equipment Depending on the building’s purpose, what it houses can be affected by the vibrations of people using the building. Universities and laboratories, for example, may have sensitive equipment whose accuracy and performance could be damaged by vibrations. Even in ordinary offices the footfall vibration can wobble computer screens, upsetting the workers.
     
  • Swaying bridges One of the most famous examples of human-induced resonance impacting a structure occurred with the Millennium Bridge. As people walked across the bridge, the footsteps caused the bridge to sway, and everybody had to walk in time with the sway because it was difficult not to. Thankfully, this feedback can only occur with horizontal vibrations so building floors are safe from it, but footbridges need careful checking to prevent it.
     
  • Human discomfort According to research, vibrations in buildings and structures can cause depression and even motion sickness in inhabitants. Tall buildings sway in the wind and footsteps can be felt, even subconsciously by the occupants. It has been argued that modern efficient 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.
     
  • Jeopardising 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 the structure and is the reason some bridges insist that marching troops break step before crossing. Crowds jumping in time to music or in response to a goal in a stadium are also dynamic loads that might damage an under-designed structure.

How to avoid it

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 engineering software is an effective method for engineers to test for and mitigate footfall and other vibrations at the design stage.

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