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.
By Laurie Andrews
Laurie Andrews is Mainmark’s Business Development Manager for NSW & ACT. Laurie is a qualified civil and structural engineer with nearly 30 years experience working in the construction and engineering industry.