Strengthening structures

Swinburne University of Technology’s Multi-Axis Substructure Testing (MAST) system is being used to test the integrity of new materials and structures, especially their capacity to withstand extreme forces, such as earthquakes.Infrastructure, such as bridges, is designed with everyday challenges like wind and service loads in mind. However, according to Javad Hashemi, Deputy Director of Swinburne University of Technology’s Smart Structures Laboratory, it is the extreme events such as hurricanes and earthquakes that need to be further understood to appropriately design said structures.

“We want structures to withstand these events. If a collapse occurs, it causes a lot of damage not just in cost, but to the economy and, of course, lives too,” explains Dr. Hashemi. “Events such as earthquakes are very complex,” he says. “They attack the structure from different directions and push it past the limits to which it has been designed.

“So that these structures can be made more resilient, we need to know how they will behave in these events – we want to know how a bridge will behave in an earthquake, for instance.”

Until now there hasn’t been cost-effective solution to exploring how these kinds of phenomena will affect a structure. Swinburne University of Technology’s new Multi-Axis Substructure Testing (MAST) system is pushing the boundaries and allowing researchers to test the integrity of a structure and its capacity to withstand extreme events, such as earthquakes.

The MAST system is used for an innovative cyber-physical testing technique called hybrid simulation. In this method, one component of a structure, for example a bridge pier, can be tested in the laboratory while it serves as part of a 3D computer model of the entire structure.

This allows researchers to accurately determine the overall structure’s capacity to withstand the dynamic effects of extreme events.

The MAST system was officially commissioned in April 2015 under the leadership of Professor Riadh Al-Mahaidi, Director of the Smart Structures Laboratory at Swinburne. It is the product of an international collaboration of private companies, universities and other research bodies.

“A lot of people were really interested in putting together a unique facility like this, which is one of the most advanced of its kind in the world,” says Dr. Hashemi.

The multi-million dollar laboratory, based at Swinburne’s Hawthorn campus, received funding from the university, the Australian Research Council (ARC) and 11 other Australian universities.

The development of the MAST system is a long story, according to Dr. Hashemi, but it essentially involved the team piecing together already established engineering practices and components into one system.

The cross head, for instance, was developed at Swinburne, while the actuator system and simulation software were created internationally. “Putting all these bits and pieces together definitely took a lot of teamwork,” adds Dr. Hashemi.

He says similar systems are already established in Canada, the US and Switzerland, but not to the same level as the MAST set up.

According to Dr. Hashemi, the facility in Minnesota in the US is perhaps the closest in capability to the MAST system, but he asserts the technology housed at Swinburne’s Hawthorn campus is unique to the southern hemisphere.

“There hasn’t been a facility before in Australia that can test a structural component under all six degrees of freedom at the same time,” explains Dr. Hashemi. These movements are forward/backward, up/down, left/right, pitch, yaw and roll.

“This facility is unique in that you can simulate all multiple axis concurrently while applying forces or deformations at the same time,” he says. “We can replicate what really happens to buildings and bridges in the case of an event, such as an earthquake.” The MAST system can apply up to 400 tonnes of force on the element at any one time.

Another exclusive feature is the ability to apply different amounts of force to different movements at the same time. “You can mix and match all six degrees of freedom. This capability is available in the US, but is unparalleled in the southern hemisphere,” says Dr. Hashemi.

Traditionally, parts of a structure – a bridge pier or column, for instance – could only be tested throughout the six degrees of freedom individually.

The beauty of the MAST system is that a single part of the structure can be put through the six degrees of freedom and then digitally incorporated into a 3D model.

This can then accurately show how an extreme event, such as an earthquake, will affect not just the single column but the overall structure.

Dr. Hashemi says the issue with current testing methodologies is that they require a full-scale model to show precisely how an earthquake will affect a structure.

“This kind of information has previously been difficult to capture. If you want to build a 20-storey building on a earthquake shake table, for example, you have to reduce it so much in size that it won’t be accurate,” he says.

According to Dr. Hashemi, there is a full-scale shake table in Japan. However, given the feasibility of building the structure and then testing it under earthquake conditions, it isn’t a cost-effective option for most projects.

These methodologies push the structure to complete collapse, providing invaluable information as to how a building or bridge will perform in an earthquake.

The MAST system delivers the same results at a more cost-efficient scale.

The data drawn from these tests can then be used to inform decision-makers during disasters or even insurance companies, particularly as it gives them a good idea of how a structure may perform in a disaster and at what point it may collapse.

Dr. Hashemi says many post-disaster inspections are undertaken by a visual assessment to see how much damage has been inflicted. Yet the major flaw is that the damage may not be obvious to the human eye alone.

He explains that not only can the MAST system help determine how much capacity and load a structure can take through its testing methodology, but even how many years a structure may have remaining post disaster, which is important for maintenance and repair works.

Another unique feature of the MAST system is its geographically distributed hybrid testing capability.

Essentially, the team at Swinburne can physically test a component in the Smart Structures laboratory while simultaneously testing another component online and elsewhere through the system’s numerical modelling software.

Dr. Hashemi, for example, undertook an experiment in his office while the Smart Structures team tested another component at the same time in the laboratory.

In short, it provides an easier and more cost-effective way to collaborate on projects internationally, and helps reduce the costs and time constraints associated with such extensive testing.

Even new materials can be trialled using the MAST system to test their suitability in infrastructure projects.

Before the MAST system was fully operational, Swinburne researchers were applying the science behind it to large-scale projects.

“The Victorian Government wanted to merge an emergency lane on the West Gate Bridge to allow for more users,” explains Dr. Hashemi. As a result, the load use of the structure would increase and so the project team had to come up with a way that could improve the structure of the bridge.

A new fibre-reinforced polymer was developed using the same MAST structural testing principles and used to help strengthen the bridge structure. “The polymer is 10 times stronger than steel and a seventh the weight,” he adds.

Dr. Hashemi says the response to the MAST system since it was commissioned has been overwhelming. “Since we started, it has been quite busy and will be busy for the next year.” He says the Smart Structures team has worked on multiple projects with organisations such as VicRoads and has had consistent support from the ARC.

The team at Swinburne is working with other facilities and universities around the world to help establish similar systems elsewhere, including in New Zealand.

“This year we’ve really focused on earthquakes with the MAST system and next year we’ll look more closely at bridges,” says Dr. Hashemi. “People have started hearing about it and, while it’s been out there for just a year, interest keeps growing and it’s becoming more public.”

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