All structures deteriorate over time. Buildings, bridges and dams might start cracking, foundations may shift, or metals can start to show signs of corrosion. Effective testing and structural investigations are designed to prevent major defects or dangerous failures.
Whether you’re evaluating the safety of an ageing elevated concrete walkway, or restoring a bell tower in a historic brick masonry church, how do you select the best testing method to assess structural condition?
Deadly results
In 1995, the Sampoong Department Store in South Korea collapsed, killing 502 people and injuring hundreds more. Cracks appeared on the fifth level two years before the disaster. Heavy air conditioning machinery installed on the roof was four times the weight the building could handle. Following noise complaints, the units were moved—not by cranes but by dragging them across the roof. Only months before the disaster, cracks were plainly visible in the concrete columns and slabs of the building.
After the disaster, The Guardian reported that inspections of other towers in Seoul ‘found that one out of seven needed rebuilding, four out of five needed major repairs, and just one in 50 could qualify as safe’. No doubt, these inspections saved lives.
Evaluating structures
International geotechnical engineer, Larry D. Olsen, has been forensically evaluating the condition of concrete-based facilities such as buildings, bridges, slabs and pavements, nuclear reactors, buildings, deep foundations, dams and tunnels since 1985. He has also performed many tests on other infrastructure containing wood, steel and masonry.
‘We need to execute assessments for ageing structures to prepare for repair, rehabilitation or replacement,’ Olsen says. ‘For instance, I was involved in the condition assessment and non-destructive evaluation of historic structures such as the Lincoln and Jefferson Memorials in Washington DC.’
As a global specialist in non-destructive evaluation and performance monitoring of structural integrity, Olsen says materials must be inspected using the right techniques. And is often the case in the world of engineering, no two structures are exactly the same. A ‘one-size-fits-all’ approach does not apply.
‘Different situations, conditions and materials—concrete, wood, metal, stone—require different techniques and testing procedures,’ says Olsen. ‘Choosing the wrong method will not provide any useful information about structural integrity.’
Testing methods: destructive and non-destructive
Methods to assess structural integrity can be both destructive and non-destructive.
Olsen explains that using non-destructive testing means there is no damage done to the structure during testing. It is non-invasive and relies on techniques like thermal imaging, magnetic particle testing and acoustic emission testing. Non-destructive methods also draw data from visual assessments using cameras, drones and, of course, the eye of an experienced engineer.
However, destructive testing causes some damage.
‘Destructive testing such as coring and lab tests are done on questionable and damaged material areas of a structure,’ says Olsen.
This may involve scraping back a damaged area or exposing the structure to certain stressors such as high temperatures, sea water, or weight pressure.
For efficiency, safety and ease, many engineers prefer non-destructive methods, including Olsen, though they can have their limitations.
‘Engineers need to assess existing structures visually, non-destructively and destructively, in an integrated fashion,’ says Olsen.
Judging integrity
While the concept of assessing structural integrity is a combination of science and physics, Olsen says it also relies on a subjective element of engineering judgement.
‘Sound and bad material conditions are the easiest to deal with, while questionable material conditions require more judgement,’ says Olsen.
Even when choosing the best testing techniques for structures subject to dynamic loads, vibration, and piping, Olsen says it is still a question of the material integrity versus the damage such as cracking and corrosion of metals.
‘You need to investigate defects, evaluate the damage and then recommend material repairs,’ explains Olsen.
Choose a testing method
Given the serious consequences of poor structural integrity evaluations, Olsen teaches testing methods at the Structural Condition Assessment of Existing Structures virtual workshop. Olsen has been facilitating this course in the USA for The American Society of Engineers since 1997. The interactive course is run exclusively by The American Society of Civil Engineers with Engineering Education Australia.
The workshop is designed for engineers from structural, civil, architectural and geotechnical or materials backgrounds. It also offers valuable insights for those working in design or inspection organisations, and governmental engineers with building facility responsibilities.
Click here to find out more.