Transport infrastructure projects: how vibrations can reveal the impact on surrounding buildings
16 April 2018
Mainmark: Visit
any Australian capital city today and you will quickly find yourself
crane spotting due to the nationwide transport infrastructure boom:
Sydney is building metro, light rail and motorways;
Melbourne has its metro expansion and highway upgrades;
Perth is working on its Metronet expansion; and
Brisbane has its own Metro and the Cross River
Rail.
Canberra is also building its first light rail.
Yet all the
tunnel boring, pile driving and demolition making way for
this infrastructure doesn’t go unnoticed by the properties along each
transport route. In the case of disputes caused by construction, there
will often be conflicting accounts on who is to blame. As our cities
densify and age, these conflicts will become increasingly more common.
The
buildings themselves have a lot to tell us on the matter. All
structures – skyscrapers, commercial buildings,
bridges, apartment blocks and the humble residential home – are in
constant motion. Minute vibrations, undetectable by humans, can tell us
a lot about a building’s stability, capacity to support the imposed
loads and the impact of nearby construction works. Buildings expand and
contract with heat and cold. Foot traffic and passing vehicles cause
movement. Crucially, these vibrations and movements can be measured and
provide the structure’s dynamic response.
Dr Alan Jeary, a structural engineer who has received the equivalent of
the Nobel Prize in his field, the Telford Award, has spent decades
researching how buildings respond to external impacts. After conducting
a series of large scale structural engineering tests in the United
Kingdom, Jeary had a ‘eureka’ moment when he realised that vibrations
can tell you everything you need to know about a building’s integrity,
including how it responds to nearby construction over time. He has since
developed a methodology to measure what he refers to as the unique
dynamic signature or ‘heartbeat’ of above-ground structures. STructural
Risk Assessment And Management, or STRAAM as Jeary’s method is now
called, represents an ideological shift in the way buildings are
analysed.
By using accelerometers sensitive enough to detect these vibrations,
STRAAM knows precisely what is happening. To collect the vibration data,
a technician installs a portable system contained in a large briefcase.
Its components consist of a data logger known as an SCG
(Structural-Cardiograph) connected to high precision accelerometers and
strain gauges. The accelerometers measure displacement, tilt and
dynamics, while the strain gauges measure deflection.
Depending on the application, the data can be live-streamed over the
internet for the duration of a project. This provides real-time data
which offers guidance to how a project is progressing and can provide a
log of incidents over the history of a project. STRAAM can be used on a
one-off application to provide a snapshot of a building’s structural
integrity, however it is best utilised when continuously monitoring. By
measuring before and after changes to a building or its surrounding
environment, it is possible to identify whether the building is
structurally sound, whether it requires remediation, or in extreme
cases, whether it needs to be pulled down.
With Australia’s sprawling cities, the need for STRAAM is growing. The
extensive tunnelling of the Melbourne Metro project has already raised
concern for iconic landmark sites across the CBD. Staff at the 19th
Century St Paul’s Cathedral have voiced their fears and some claim
Federation Square “will be rocked to its foundation”. Even the metro
project’s home webpage concedes that some impact is inevitable. At
present, however, only the traditional monitoring methods are being
applied. STRAAM would be able to provide more transparent and objective
insight into the impact of these projects on surrounding structures.
--ENDS--
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