University of Alberta's Robert Cheng is working on technologies that will allow structures to communicate otherwise invisible information about the stresses they are subjected to, allowing engineers greater ability to build and repair appropriately. "My goals include extending the useful life of structures, greatly reducing maintenance costs, and cutting the need to regularly replace or refurbish infrastructure projects," Dr. Cheng says. "The simple fact is that going forward, we will not have the resources to continue doing things the way we have for the past 50 years."
By Terrence Belford
Anyone can talk to buildings, bridges and statues. University of Alberta professor Roger Cheng can make them talk back.
Dr. Cheng, chair of the Edmonton school's civil and environmental engineering department, has come up with ways to first create new structural components from space-age materials such as carbon fibre, and to then find ways to install optical fibre sensors in them.
As a result of his research, when engineers around the world want to know the stresses, strains and corrosion taking place inside seemingly solid structures, the structures themselves can provide the answers.
Sophisticated sensors monitor the health of the structure and the collected data is transmitted digitally to a central monitoring station. No more waiting for components to fail - maintenance crews can take preventive action instead.
Dr. Cheng says tragedies such as the collapses of bridges in Laval, Que., and Minneapolis earlier this year can be avoided if his new technology were widely adopted. Where systems based on his research have been installed, they appear to do the trick, he notes.
Bridge reports back
For example, the Confederation Bridge, linking Prince Edward Island with the mainland, has already reported back that it is over-designed and could have been built more cheaply; the sheets of sea ice that engineers expected to batter its piers have yet to appear.
Winnipeg's famous Golden Boy, the statue that has topped the Manitoba Legislature since 1919, now reports back regularly on the state of the steel-alloy bar that fixes it to the roof.
And a bridge in Hamilton, Ont., tells city engineers how deeply winter road salt has penetrated its concrete deck and how close that salt is to corroding the deck's reinforcing bars.
"We believe that systems that monitor the ongoing health of structures will inevitably change our whole approach to structural design and maintenance," says Aftab Mufti, scientific director of ISIS Canada, a research network based at the University of Manitoba.
"I call what [Dr. Cheng] is doing civionics," says Dr. Mufti, a professor of civil engineering. "In the aircraft industry, they combined aviation design with electronics to get today's avionics; the auto industry followed suit combining mechanical engineering with electronics to create mechtronics.
"We are doing the same for civil engineering."
Dr. Cheng and other ISIS researchers are trying to change the philosophy of infrastructure design: They want to replace today's disposable structures with those capable of lasting centuries.
"My goals include extending the useful life of structures, greatly reducing maintenance costs, and cutting the need to regularly replace or refurbish infrastructure projects," Dr. Cheng says. "The simple fact is that going forward, we will not have the resources to continue doing things the way we have for the past 50 years."
Currently, when engineers set about designing a bridge, they assume there is a one in 10,000 chance that one of its components will fail within 50 years, Dr. Mufti explains.
"What we want to do is change that approach," he says, adding that engineers start with assumptions based on historical data - and that data may not be pertinent.
"If we make structures talk to us on an ongoing basis, we can not only accurately say when a component is approaching the failure point but we can also accumulate accurate data in real-time conditions on which to base future designs."
Dr. Cheng's work started in the mid-1990s with research into using carbon fibre materials to replace traditional building materials. He created such innovations as reinforcing rods that would not corrode and have the same elastic properties as concrete, as well as a form of wall reinforcement that rolls on like wallpaper.
"They have used the carbon-fibre wallpaper on masonry buildings, such as schools, which have been damaged by earth tremors," he says.
Later, he moved into structural health monitoring by attaching hair-thin, glass-fibre sensors to building materials.
These sensors gauge stress, vibration, temperature, humidity, chemical accumulations such as salt, and any other factors that might affect the health of the structure.
The information is transmitted as light signals to a device attached to the structure; there the light signals are converted to digital form and then transmitted electronically to a central monitoring station, which can be thousands of kilometres away.
"To date we have done maybe 50 projects in Quebec, British Columbia, Manitoba and Alberta," Dr. Cheng says. "If you look at the Confederation Bridge, there is a steel cabinet attached to the side. That is the converter."
Acceptance by customers
The idea of structural health monitoring has now been embraced by 650 trained professionals across Canada, according to Dr. Mufti. But acceptance by customers is slower in coming, says Garth Fallis, vice-president of Vector Construction Group of Winnipeg.
"We have been doing it for the past five to six years but at this point projects are few and far between," he says. "Part [of the reason] is that monitoring adds to construction costs, and part is because it is still pretty much experimental."
However, Mr. Fallis is confident that structural health monitoring will catch on within 10 to 15 years.
"In the past we calculated what we thought strains would be, now we are starting to understand the great benefits of design based on the data [that] monitoring gathers."