Statement on the Australian Building and Construction Commission
“The Business Council of Australia applauds the Federal Government for working with the crossbenchers to pass the legislation to re-establish the Australian Building and Construction Commission (ABCC),” Business Council Chief Executive Jennifer Westacott said.
“Four Royal Commissions over 40 years have provided unassailable evidence that the building and construction industry needs its own regulator. We are pleased the Senate recognised the inadequacy of current arrangements and took action to fix this problem.
“Today’s decision shows that the parliament can work together to pass important legislation that improves Australia’s competitiveness, a critical factor in driving our ongoing prosperity and creating meaningful jobs in a volatile world.
“We would like to pay particular tribute to Minister Cash for her steadfast efforts to pass the legislation and her willingness to engage with business and the community to find a solution to issues that are of national significance.
“As the third biggest employer in the Australian labour market, a well-run and efficient building and construction industry is vital for the Australian economy. The Business Council is pleased we now have a mechanism to ensure the poor behaviour of a few workers cannot continue to disrupt the hard work of many.
“We believe all Australians have a right to feel safe in their workplace. The ABCC will be empowered to deal with the systemic corruption and unlawful conduct identified in the industry. It will be an impetus for cultural change and ensure workers, unions and employers are all responsible for ensuring their workplaces operate lawfully.
“It will restore community confidence in our workplace relations system and help ensure the construction industry has the capacity to continue to make a valuable contribution to growing the national economy.”
Read the November 2016 issue of Construction Global magazine.
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.