Autumn Statement: Doubling the UK’s housebuilding budget
Today George Osborne announced that the UK’s housebuilding budget is to be doubled. Faced with some difficult decisions regarding public spending cuts, the Chancellor chose housing by prioritising investment in new affordable homes. The government has confirmed plans to build 200,000 starter homes with 20% discounts for under-40s, 135,000 shared ownership homes, 10,000 rent-to-buy homes and 8,000 specialist properties for the elderly and disabled. This amounts to a £7bn public investment in new homes – a concerted effort to give people a helping hand onto the housing ladder.
This comes as good news for the UK where there’s growing demand for affordable housing. However, the plans haven’t come without criticism.
Ben Derbyshire, Chair of the Housing Forum said: “We have some concerns about demand side policies which rob social housing Peter to pay home owning Paul, as a balanced housing market for all needs affordable homes to rent. The boost to private house building on the supply side should now be accompanied with measures to ensure quality, and embrace modern techniques and manufacture.”
There’s also a worry that there aren’t enough skilled workers to keep up with the build of more housing. Brian Berry, Chief Executive of the Federation of Master Builders, said: “‘George the Builder’ will need a new generation of ‘real’ builders to make his vision for housing a reality. We’re already seeing housing developments starting to stall because the cost of hiring skilled tradespeople is threatening to make some sites simply unviable. Unless we see a massive uplift in apprenticeship training in our industry, there won’t be enough pairs of hands to deliver more housing on this scale. That’s why we’re keen for the government to tread carefully when applying the proposed Apprenticeship Levy to the construction industry.”
Berry concluded: “The Chancellor clearly recognises that the crisis of home ownership is inextricably linked to a crisis in house building. We therefore hope that in order to address both, the government will do everything it can to increase house building capacity. SME developers will have an important role to play in delivering the smaller scale sites across the country. The last time we built in excess of 200,000 homes in one year was in the late 1980s when two-thirds of all homes were built by small developers. SME house builders now only build little over one quarter of all new homes which points to another serious capacity issue – we need more small house builders to enter the market and also for SME house builders to crank up their delivery of new homes in order to build the Chancellors 400,000 new affordable homes.”
Steve Perkins, Director of Urban Development at global construction consultancy Turner & Townsend, echoed these concerns. He said: “There is still the awkward question of what will happen when the surge of new building unlocked by these measures collides with the lack of capacity – both in the construction industry itself and in the planning process.
“As demand from developers increases, the shortage of skilled workers is likely to drive up construction costs, and stretch planning authorities – already pared back by local government austerity – to the limit.”
There’s no doubt that these plans hail good news for the UK’s construction industry but there’s a lot to be worked out in how it’ll be implemented before those in this sector are convinced.
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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.