May 16, 2020

Balfour Beatty Withdraws from Carillion Merger talks over Parsons Brinckerhoff sale

Balfour Beatty
Carillion
Parsons Brinckerhoff
Mergers and
Admin
1 min
Balfour Beatty workers at Thameslink, London.
Balfour Beatty has withdrawn from talks with Carillion over a merger after disagreement over the sale of consultancy firm Parsons Brinckerhoff.Balfour s...

Balfour Beatty has withdrawn from talks with Carillion over a merger after disagreement over the sale of consultancy firm Parsons Brinckerhoff.

Balfour said the termination occurred following Carillion’s “wholly unexpected decision” to only proceed with the deal if Parsons Brinckerhoff remained part of the new combined entity.

Balfour’s statement continued: “It is also contrary to the joint announcement released on 24 July 2014 which confirmed that the sale of Parsons Brinckerhoff would be unaffected by the merger discussions and also a presentation to Balfour Beatty’s Board by Carillion on 28 July 2014.

“This change in the proposed terms is not acceptable to the Board of Balfour Beatty.”

The two major contractors had announced the merger talks last week

Both companies’ shares fell on the news this morning, with Balfour Beatty’s down 5.5 percent and Carillion’s falling 4.4 percent.

Balfour Beatty said it will now proceed with its own business plan including the Parsons Brinkerhoff sale, which it said was “well underway”, and that it would "actively progress” its search for a new CEO.

Had the merger been successful, Carillion boss Richard Howson was expected to take the job at the new combined entity.

 

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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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