How does a building respond to extreme winds? How much force does it take to affect the structural integrity of a building? Answers to these questions are being addressed with the help of University of Nebraska-Lincoln College of Engineering research thanks in part to the controlled demolition of Cather and Pound Halls on campus last December.
While it took less than 60 seconds to demolish more than 50 years of memories to the people who lived and worked in the residence halls, the data gathered has proven invaluable.
“This, to me, is real cutting-edge research,” noted Daniel Linzell, Voelte-Keegan Chair and professor of civil engineering, who is studying the “during” and “after” effects of the implosion. “There’s some really good data we’re still putting together as a result of this event.”
The university’s razing of the two buildings on Dec. 22 helps engineering faculty and graduate student researchers study how large, multi-story buildings react to extreme event scenarios, such as earthquakes, turbulent winds and explosions.
Several weeks before experts from Controlled Demolition Inc. imploded the former residence halls along 17th Street, accelerometers were installed on interior columns to measure the frequency of vibrations within Cather and Pound. The students used this information to conduct behavioral surveys of the two towers and to create and refine models showing how the towers moved. Combined with a survey of Cather Hall completed two years ago — when the hall was still open for student housing — the data provides a clearer picture of how buildings behave as their structural integrity changes.
“These sensors, the accelerometers, allowed us to create a computer model and ascertain dynamic range of response of the buildings,” Linzell said. “For example, how are the dynamic properties changing as parts of the buildings are removed prior to demolition?”
Thirty-two accelerometers (27 in the north tower and five in the south) were installed to record how buildings behaved during the implosion sequence. The accelerometers recorded less than a minute of data before they were destroyed. According to Linzell, some of the sensors were still working even after the buildings crumpled to the ground.
“Sensor signals were accessed remotely during and immediately after the implosion,” he stated. “What we discovered is that some sensors, believe it or not, were still working. We probably obtained some of the richest data from those accelerometers.”
Nebraska engineers were able to document how dynamics of the two 13-story structures changed when the buildings fell to the ground around 9 a.m. Led by Richard Wood, assistant professor of civil engineering; Christine Wittich, assistant professor of engineering; and Linzell, data collected on the 22nd featured two primary goals: expand the engineering field’s understanding of how large structures react to extreme events, and use it to refine engineering models that would, in turn, be used improve the building resiliency to these events.
Wood’s research focuses on dynamics, analyzing video and data from the implosion to learn more about post event information, including where first responders should go after a structural event of this significance. Wittich is studying effects on adjacent buildings, particularly due to ground movement caused by the implosion, while Linzell’s research centers on extreme demands on structures brought about by events, and making buildings safer during and after their construction.
“Our research looks at being able to construct buildings in the future that can withstand these type of events,” Linzell pointed out, “ways we can retrofit older buildings to withstand violent collisions or explosions. This project allows us to improve tools, means and methods that can, hopefully, someday prevent substantial damage caused by extreme events.”
Demand for information after demolition was almost as swift as implosion itself, with outside entities like the National Institute of Standards and Technology (NIST) and other organizations requesting UNL’s data.
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