May 16, 2020

Small Scale, Big Impact: Infrastructure and Economic Regeneration

Leo Quinn
Balfour Beatty Group Chief Executive
Small scale
big impact: infrastructure and economic regeneration
Catherine Sturman
2 min
Small Scale, Big Impact: Infrastructure and Economic Regeneration
Balfour Beatty has published theirpaper,Small scale, big impact: infrastructure and economic regeneration, which draws on its considerable experience an...

Balfour Beatty has published their paper, Small scale, big impact: infrastructure and economic regeneration, which draws on its considerable experience and understanding of the link between infrastructure and economic regeneration.

The company examines the role small scale, quickly implementable projects which can play in boosting economic growth nationally in the short to medium term, while simultaneously providing a longer-term structural contribution to the economy for example, by addressing congestion on the roads.

Such ‘shovel ready’ schemes will provide the construction industry with the pipeline and certainty to invest in training future experts who will be needed to deliver larger scale projects such as HS2 and the third runway at Heathrow.

Leo Quinn, Balfour Beatty Group Chief Executive, said: “Whilst major infrastructure investment will be vital to the strength of the UK over the mid-term, we believe there is also a way for the government’s industrial strategy to drive rapid economic stimulus, with considerable geographic precision.

“As of today a number of road, rail, public realm, flood defence and construction projects exist which meet the Chancellor’s tests, in many cases have been approved, but are stalled by lack of funding. Taking advantage of current low borrowing costs to select and implement those with potential to bring maximum impact on a localised basis would quickly disperse uncertainty and set the country on the path to an economic growth that works for everyone.”

Key recommendations within the paper include the need for a solid project pipeline; the importance of considering alternative economic modelling which makes a more robust economic case for infrastructure investment more broadly across the country; ensuring that fiscal stimulus is not directed solely towards new infrastructure; and that there is an early and integrated policy response to the skills shortage.

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Read the November 2016 issue of Construction Global magazine

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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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