The great skill crisis continues
The skills crisis in construction is seemingly spiralling out of control as 73 percent of contractors say they are struggling to fill roles for “higher skilled” staff.
A survey by the CBI and education specialist Pearson said that Government plans to boost apprenticeships “will not deliver the high-quality, business-relevant training needed” to support the development of the construction sector.
Katja Hall, CBI Deputy Director-General, said: “The Government has set out its stall to create a high-skilled economy, but firms are facing a skills emergency now, threatening to starve economic growth.
“Worryingly, it’s those high-growth, high-value sectors with the most potential which are the ones under most pressure. That includes construction.”
The Government announced plans for a levy on all major employers in the Budget. Construction already has its own training-levy system run via the CITB.
Hall said: “The new levy announced in the budget may guarantee funding for more apprenticeships, but it’s unlikely to equate to higher quality or deliver the skills that industry needs.
“Levies on training already exist in the construction sector where two-thirds of employers are already reporting skills shortages.
“Employers have a critical role in upskilling the workforce, but part of the deal must be for real business control of apprenticeships to meet their needs on the ground.”
The survey also highlighted continuing fears among employers about the standard of teaching in schools. Over a third of firms report some concerns with school leavers’ literacy/use of English (37 percent), basic numeracy (37 percent) and nearly half on communication skills (49 percent).
“Employers consider attitudes and aptitudes more important than any specific qualification or skill, other than practical literacy and numeracy.
“They also want to see young people gaining a greater understanding of the world outside the school gates, by inspiring pupils about career opportunities from a much earlier age and by putting work experience back on the agenda for all young people,” says Hall.
Steve Radley, Director of Policy at the Construction Industry Training Board, said: “Levies alone won’t deliver quality apprenticeships – it is also critical to have proper forecasting of skills demand and better engagement with training providers to meet employer needs.
“But well-designed levy systems, if they have buy-in from employers, can play a positive role in tackling the skills challenge.”
Why engineers must always consider human-induced vibration
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.