MILWAUKEE — Records released by Glendale show the parking structure at Bayshore Mall had a stability that is standard for structures like it, according to a UW-Madison engineering professor.
“This is a typical garage,” Gustavo Parra-Montesinos said. “We have standards that we use to calculate loads and to calculate the strength.”
Parra-Montesinos helped the I-Team better understand the documents released by the City of Glendale about the parking structure. He says the structure was expected to have the ability to withstand 25 pounds per square foot of snow on the top floor, though he says most structures can hold much more than that.
“They probably design for about 90 to 100 pounds per square foot,” Parra-Montesinos said. “I would not expect just snow sitting there to create a load that would be large enough to cause a failure of these double t-beams. If you have a significant pile of snow, you can get more [weight] than that.”
The parking structure at Bayshore Mall was given the approval to open on Oct. 31, 2006, according to documents released by the City of Glendale. Parra-Montesinos was not involved in the construction of this structure, but he understands what goes into designing a safe structure.
He says, engineers calculate an elaborate equation with several variables to ensure the lowest possible risk of failure.
“We calculate strength for bending, shear strength,” Parra-Montesinos said. “Then you have what we call load combinations. Dead permanent loads with live loads or snow. There are different percentages when you combine them. You do not design for what you expect. You design for more than that.”
On the day of the collapse, Fire Chief Robert Whitaker mentioned there is a confirmed cause of the collapse. However, he said, “We’re not positive snow was the cause of the collapse, but we’d like to think it’s involved.”
However, Parra-Montesinos says the snow, as it originally fell, shouldn’t have been a problem based on his understanding of a typical parking garage. He says the design plans and calculations engineers do keep even the heaviest snow in mind.
“We increase the magnitude of the loads to look into extreme or very rare events,” Parra-Montesinos said. “We don’t design for normal loads. We design for much higher loads for events that are extremely unlikely to occur again. The probability of failure is not zero, but the idea is that when you combine all those factors, the probability of failure is extremely low.”
“It was probably the most amount of sleet we’ve seen in a storm system since the 70s,” TMJ4’s Chief Meteorologist Brian Niznansky said.
WATCH: Brian Niznansky helped explain what made this story so different.
“We can’t make an assumption about how much snow or sleet is in that pile of snow,” Niznansky said. “But what we do know, whatever was stacked into that pile was significantly heavier than the standard snow that I’m sure was stacked there many times before.”
Sleet is denser and heavier, according to Niznansky. He says sleet tends to be roughly four times heavier than average snow. While he wouldn’t venture a guess as to how heavy this snow pile was, he did put it in perspective.
“Say you have your pile of sleet stacked up there," Niznansky said. "If it’s normal snow you would have had to squeeze in four times that pile into that same location [to equal the weight]."
Police body camera video from the day shows an incredible amount of snow on the bottom floor of the garage after the collapse.
“It seems like a significant pile of snow,” Parra-Montesinos said. “It has to be a significant pile of snow, not just any pile of snow. I assume that snow was compacted as it was being piled up so that adds to the weight that’s concentrated in this area.”
Niznansky points out, a regular snowfall is roughly 6.2 pounds per cubic foot whereas this snow was more like 26 pounds per cubic foot. So, if a cubic foot of sleet was stacked on top of a cubic foot of sleet, it would weigh 52 pounds and another cubic foot on top would way 78 pounds, and so on.
It will likely be months before investigators finish their work and declare the true cause of the collapse, but Parra-Montesinos hopes this sends a message to the public.
“The fact that we’re talking about the probability of this pile of snow leading to the collapse should be enough of a warning for people managing other parking structures to make sure they don’t allow this sort of accumulation of snow to happen,” Parra-Montesinos said.
Police body camera video shows a commercial snow removal business on the scene the day of the collapse but calls to the business were not returned.