Predicting Failure in Ice Shelves | Haim Waisman
|Haim Waisman, assistant professor of Civil Engineering and Engineering Mechanics|
The I-35 bridge collapse in Minneapolis in 2007 killed 13 people and resulted in untold economic disruption for the Upper Midwest. It also brought into stark relief a problem with the nation’s infrastructure that is, by its very nature, bound to get worse with time: it is old and getting older every day.
For Haim Waisman, assistant professor in the Department of Civil Engineering and Engineering Mechanics, the aging infrastructure also highlights a more general characteristic of any structure— everything breaks eventually. For that reason, Waisman is developing computational techniques to help understand how and why things fall apart, and how this may be predicted and prevented.
“Fractures govern our lives,” he said. “Everything is connected by fractures.”
Fractures also play a role in nature, and Waisman has recently turned his attention to a dramatic example—the collapse of ice shelves in Greenland and Antarctica. As the climate warms, water from melting ice seeps to the bottom of glaciers, allowing them to slide more easily over bedrock and forming networks of cracks in ice shelves. Over the course of about a month in 2002, 1,250 square miles of the Larsen B Ice Shelf in West Antarctica shattered, sending icebergs into southern shipping lanes and permitting glaciers linked to the shelf to speed up. Since then, several other shelves have collapsed, raising concerns that the massive ice cap covering the continent is on the move, threatening sea-level rise around the world.
Waisman is refining computational methods known as extended finite elements and multiscale modeling to design high-strength, nano-composite materials that might one day shore up aging structures, such as pipes and bridges, in corrosive environments. He also has developed a noninvasive method of detecting fractures in things such as airplane wings using measurements from only a few common stress sensors.
In particular, he has been using his methods to study how suspension bridge cables age. The main cables are made of thousands of wires clamped and wound together. When a wire breaks, the loads it carries are redistributed to neighboring wires. Understanding and predicting the fracture response of the entire cable involves taking into consideration as many as 50,000 wires wound into a tightly compressed bundle more than two miles long and requires a supercomputer. He has found that, when a wire breaks, friction between the remaining wires can effectively transfer the strain throughout the cable bundle without compromising the entire bridge. That’s a relief for the millions of people who daily cross the graceful but aging bridges that lead into and out of Manhattan.
Understanding how things like ice shelves and bridges break and fail is a necessary first step to understanding the inevitable, inexorable changes that are going on all around us all the time.