When structures collapse because of an earthquake or another natural disaster, the explanation is easy. When they collapse seemingly out of nowhere, that’s a different story — one that Sarah Orton intends to solve.
Orton, MU associate professor of Civil and Environmental Engineering, and Ying Tian of the University of Nevada, Las Vegas recently received a three-year, nearly $450,000 grant from the National Science Foundation for their proposal, “Time-Dependent Response of Reinforced Concrete Buildings Near Collapse.”
The goal of the project is to study structures under high amounts of sustained load and discover why, in the absence of any change in loading or natural disasters, they collapse.
“The question is how does the structure’s capacity change when you get to high level sustained loading — does it drop off if you keep that load up at a high level for a long time? Nobody knows,” Orton explained.
“There’s been lots of cases of buildings standing there, looking fine, just with some cracks in some columns here and there, but then it just falls down. What leads to that collapse? Something has to trigger that in some way. We think because the load is sustained, the structure is actually losing its ability to carry the load. And at some point, it can’t take it anymore.”
The proposal seeks to address the following specific questions:
- What are the time-dependent strength and stiffness characteristics of a reinforced concrete member under sustained high stresses?
- What is the system level response of a reinforced concrete building near collapse when a critical component has experienced a failure?
There will be some modeling work involved, but most of the research will be conducted experimentally. Orton and Tian will construct various structures and place them under high levels of sustained loading and work to uncover what leads to eventual collapse.
If Orton and Tian can uncover just what causes these structures to collapse, it could have remarkable impact on safety as well as best practices for repair.
“I’m glad NSF funded it,” Orton said. “In a lot of previous collapse cases I looked at, the building is there and people think it’s fine, and then it falls down. … That’s part of the proposal. What are the warning signs people really need to worry about? ‘Is that really a bad crack or is that a crack I don’t need to worry about?’”