The razing of Cather and Pound residence halls on Dec. 22, 2017, was quite a sight to see … and hear.
But for the team of University of Nebraska-Lincoln civil engineering researchers collecting data to study the demolition, it was a moment of silence during the blast sequence that may be the most resonant.
Once the demolition crew had set off the three-second series of explosions meant to initiate the collapses, it took less than 10 seconds for the two 13-story towers to collapse onto themselves and create twin piles of rubble.
For researchers Richard L. Wood and Christine E. Wittich, both assistant professors of civil engineering, and Daniel Linzell, associate dean for graduate and international programs and professor of civil engineering, it was also about collecting data from the sensors and accelerometers they had placed in and around Cather, Pound and three nearby structures and from video and audio collected during the event.
It was the beginning of their quest to sift through what Wood calls “a tiny, little mountain of data” to understand how high-rise buildings and adjacent structures react to extreme loads.
While sorting through the data, it was a less-than-two-second lull after the blasts and before the buildings began to fall that stands out.
“We have noticeable acceleration (vibration) spikes in the data due to the blast – all this excitation and then relative silence. About 1½ to 2 seconds later, the spikes come back,” said Wittich, who is studying how the blasts impacted adjacent structures and the surrounding soil. “That period of time was the loads being redistributed throughout the buildings, leading to the collapse. Now, instead of one data set, we have two – the response due to the blast loads and that due to the collapse.”
Linzell is creating mathematical models that, among many things, will help to understand and predict load redistribution. He wasn’t expecting audio data to play an important role in the research, but now recognizes it might be the linchpin that brings everything together.
“I figured we would (use some audio data), to help us understand what happened within the buildings, but possibly not. I don’t think we utilize audio clues enough with these types of studies,” Linzell said.
“How do we more directly link the frequency of the blast audio or the magnitude of that noise to what actually happens physically? As we sit here and talk, I think the audio is the one thing we could publish that would be a huge contribution to understanding the response of structures to extreme loads.”
It wouldn’t have been possible if not for state-of-the-art technology – sensors, unmanned aerial vehicles (UAVs or drones), and computer software with 3D mapping and modeling programs. Most of that technology was overseen by Wood, whose primary task was characterizing the structure for months in advance right up through its collapse.
The team – which included a group of graduate students, many of whom volunteered for the project – spent three weeks placing hundreds of sensors in the towers and three nearby buildings and nearly six miles of wiring to hook it all up. There is also video footage from a fleet of drones, including the ones operated by Wood closely coordinated with other academic teams and those from other approved pilots.
Though everything seemed to go as planned with the demolition, there were still stressful moments for the research team that morning.
“It was rush-rush, push-push until the actual buildings went down,” said Wood. “The night before, I was still prepping, trying to make sure the data acquisition for Cather and Pound halls and the drones flew because they’re remote-controlled. I had a couple hours of sleep and then went rushing out the door at 5 a.m. to install the final sensors before they cordoned off the area.”
For Wittich, the panic set in literally three minutes before the first blast.
“It was scheduled to happen at 9 a.m. and at 8:57 one of my data acquisition systems in one of the buildings had an error. I literally had to rush up until the last minute to ensure that it would record what I set it up to record.”
And there were a few surprises for the research team when they started analyzing the data. Among them was just how much force the collapsing buildings created.
The hundreds of spectators gathered along Vine Street that cold morning came to watch the buildings come down and witness history. The moment was bittersweet for the researchers.
“We had three weeks’ notice that we could do this project, and we had to rush to do what might usually take up to a year of preparation,” Wood said. “What a shock it was that all of our efforts (the instrumenting of those buildings) were gone in a flash.”
Now, the researchers are trying to make sense of the mountain of data that remains. Supercomputers at Nebraska’s Holland Computing Center are making that process so much easier, Linzell said.
“The resources we have here are right up there with any of our peer or aspirational institutions, if not better,” Linzell said. “the Holland Computing Center is supporting CERN (the European Organization for Nuclear Research, which is located in Switzerland and operates the largest particle physics laboratory in the world), and Dr. Dave Swanson, who runs it, has been great. They are wanting and willing to help us expand our work and do more sophisticated models and they have shifted resources around to facilitate doing things in as optimal a fashion as possible.”
Though the Cather and Pound dormitories are gone and the process of turning that area into green space for the university continues, the engineering research team is confident there will be a legacy that lives on for many generations.
The data collected will be used in a graduate civil engineering class taught by Wittich in the spring, and a few graduate students, including one advised by Wittich and Wood, are using the project in their theses.
And that morning, which Linzell said was reminiscent of the hours before a Husker football game, may be important for the future of the university and beyond.
“People came and brought breakfast and they were tailgating. That made it, from my perspective, cool,” Linzell said. “The fact that people who aren’t scientists discuss the event with me is heartening.”
“Families came, too,” Wood said. “We’re always looking for the new generation of engineers. I imagine we inspired a few.”
“I want to believe we did,” said Linzell. “Honestly, I think we can say we did.”
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