TzuYang Yu Is an Expert on Structural Health Monitoring of Civil Infrastructure
10/16/2024
By Edwin L. Aguirre
This year’s Atlantic hurricane season has been very active, with two extremely powerful tropical cyclones – Helene and Milton – devastating large swaths of Florida, Georgia, the Carolinas, Tennessee and other areas. The back-to-back storms claimed the lives of more than 270 people and caused damage totaling more than $70 billion. Once-vibrant communities were leveled.
What happens to homes, buildings, roads and bridges during a powerful storm? We asked Prof. TzuYang Yu in the Department of Civil and Environmental Engineering for some insights. An expert on structural engineering and concrete materials, Yu directs the university’s Non-Destructive Testing/Structural Health Monitoring Lab, the Electromagnetic Remote Sensing Lab and the Structural Engineering Research Group. He earned his master’s degree and Ph.D. in civil and environmental engineering from MIT before joining the UMass Lowell faculty in 2008. Here are excerpts from our interview.
Q: What makes a hurricane so destructive?
A: For buildings, especially residential homes and factory warehouses, strong wind gusts can destroy roofs and exterior walls by pushing on the exposed side of the structure and sucking on the opposite side. For bridges, scouring induced by flooding can destroy bridge piers and their foundation, consequently collapsing the bridge girders. Storm surges can bring down trees and freestanding structures such as utility poles and transmission towers, resulting in widespread power outages. Extreme rainfall can also threaten the lives of residents in low-lying or mountainous terrain with flash floods and landslides.
Image by NASA
Q: Why do some structures remain largely intact after a severe storm while others do not?
A: This is because the design and construction of structures are not entirely identical. Building codes are updated every few years to reflect changes in construction materials and construction techniques as well as the importance, or frequency, of certain types of structural loading. As a result, some structures can survive a severe storm and others cannot. Even though structures may look very much alike from the outside, they can be very different in terms of their load-bearing capacity. Another factor is the level of loading. Not every structure is subjected to the same level of loading, or force, when a storm passes through an area. Those subjected to stronger wind gusts, obviously, are more likely to collapse if they do not have what it takes to withstand the storm.
Q: From an engineering perspective, are some communities more vulnerable to natural disasters? And if so, why?
A: Buildings on low terrain are much more vulnerable to severe storm surges when wind gusts are combined with flooding. Since a residential house is basically hollow, its exterior walls cannot resist high water pressure – they are not designed to resist flooding. Therefore, the walls can collapse, and the house can get washed away. On the other hand, buildings on high terrain are more vulnerable to wind gusts. In any case, residents are never safe in their homes when facing the brunt of a severe storm unless the homes are built with strong materials like reinforced concrete. Masonry houses have exterior walls strong enough to withstand flooding, but their roof can still fail under strong wind gusts.
In general, residents caught in a severe storm face two life-threatening dangers: the collapse of buildings, and drowning from floodwaters.
Image by U.S. Air National Guard
Q: Photos of hurricane-battered communities show huge piles of debris lining the streets. How dangerous are they during a powerful storm?
A: During a powerful storm, the debris can either float or move with the floodwater, impacting structures or blocking bridges and dams in a bottleneck. They can also fly in the wind like projectiles, striking buildings, vehicles or pedestrians.
Q: Is it possible to retrofit homes and buildings to harden them against future hurricanes/natural disasters?
A: Yes, it is possible to retrofit or strengthen houses and buildings against some threats such as wind gusts, but not all of them. For example, stopping storm-induced flooding from getting inside a house or a building can be challenging and costly, and sometimes even impossible when the foundation was not built using strong structural materials such as reinforced concrete.
Q: Climate change is causing more frequent, more intense tropical cyclones as well as rising sea levels. What can local officials and the state/federal government do to mitigate these effects?
A: There are at least three aspects in hazard mitigation against climate change. First are life-threatening dangers: A notification system that can provide early warnings to the public is a must, as well as a network or supply chain of support to provide shelters, food and water to keep people safe. Second is precautionary structural retrofit: Old buildings should be assessed to identify and prioritize possible repairs that are needed. And third is long-term urban planning: Climate change has been altering coastlines, landscapes and underground water tables in the U.S. The environmental risk from climate change to human-made structures should be assessed and taken into account in urban planning.
Q: Is saltwater intrusion due to rising sea levels now a major concern for coastal homes, buildings and other infrastructures?
A: Seawater rise and infiltration into the freshwater region is a known threat to engineering structures. Accelerated corrosion of steel components in reinforced-concrete structures such as foundations, tunnels and pipelines, due to chloride ions in seawater, can weaken the structural integrity of concrete structures in a few years, leading to potential collapse. Chloride and sulfate ions in seawater can also attack concrete, a process known as chemical corrosion that could decrease the concrete’s load-bearing capacity.