University of Wisconsin expert: Barn collapses blamed on lack of engineering
Many of the agricultural buildings that collapsed earlier this winter in the Upper Midwest failed due to a lack of proper engineering rather than excessive snow load, according to a UW-Madison building professor David Bohnhoff.A professor in the Biological Systems Engineering Department at UW-Madison said most modern farm structures are engineered to handle an extreme snowfall such as that which occurred in mid-December. At least a dozen barns - most 10 to 15 years old but some standing only a few years - collapsed in western Wisconsin and southeastern Minnesota after a blizzard dumped as much as 2 feet of snow. Properly engineered and constructed buildings would not have caved under such a snow load he told The Country Today. "We build buildings better today than we ever have in the past," he said. Bohnhoff visited six of the buildings that experienced major failures and attributed each of their issues to the absence of engineering. The barns were erected by four different builders, he said. Blaming all of these building failures on snow load "perpetuates a huge problem" in the agriculture industry, Bohnhoff said. In most cases, farmers were led to believe they had purchased a properly engineered building. "Sometimes there's not full disclosure about what's going on," he said, adding that the construction of large buildings is a science, and there's no science behind non-engineered buildings. To protect themselves and their investment before construction, farmers should request from builders a complete set of structural calculations showing that all building elements have been designed to meet the structural performance criteria of the InternationalBuilding Code. He said Farmers also should demand that these calculations be sealed by a qualified. Registered professional engineer who specializes in post-frame building design. "If all they hand you is a truss design produced by a technician at a local lumber yard, find another builder," he said. Bohnhoff said many people are unaware that UW-Madison has the world's most prolific post frame building research program. His position is dedicated to the education about and research of Ag facilities. He focuses on post-frame buildings, which make up the majority of Ag structures, especially in the Upper Midwest with its many livestock farms and the need to shelter animals from weather extremes.
Because of the Ag industry. The region is home to some of the biggest post-frame building companies in the U.S. Bohnhoff said. The number of large building failures over the past few years is of major concern to engineers and researchers, he said.
"This isn't the first time. It pops up in pockets routinely, and, by and large, only with buildings that aren't engineered:' he said.
Numerous buildings went down last winter in Iowa and Minnesota, prompting discussions among engineers at last year's National Frame Building Association annual meeting. They concluded that the buildings lacked engineering, Bohnhoff said. Although agricultural buildings in Wisconsin and many surrounding states are exempt from the building code - which establishes minimum performance criteria - Bohnhoff said that doesn't mean builders should skimp on engineering. Farmers should demand it. He said many builders tell farmers they don't need their buildings engineered because of the exemption. While this is true, it's fool-hardy, especially for facilities in which people will be spending much time.
"It is one thing to exempt agricultural buildings from the state building code; it is another thing to not engineer them," Bohnhoff said. "These buildings did not fail because of a state building code exemption. They failed because they were not properly engineered and/or constructed."
He said there is no reason for most agricultural buildings to fail much more frequently than other types of buildings. "There was absolutely no reason for these buildings to fail; this was not a big snow load at all," he said. "To claim that these buildings were designed to meet lower snow levels than other buildings in the area is a misleading statement given that these buildings were clearly not engineered."The buckling that resulted in building failure still is evident in barn components that haven't come down yet, he said. "In virtually all cases, people are confusing the independent sizing of a single component for a balanced snow load (i.e., a typical truss design) with building engineering," he said. "These are worlds apart." Bohnhoff said this is a huge problem, and most farmers don't know the difference. They need to better understand what sets reputable builders apart. "We don't want farmers to think that everything's fine out there when it certainly is not," he said. Bohnhoff said there wasn't a single diagonal brace on the numerous rows of continuous lateral bracing in any of the very large buildings he visited. "This was somewhat shocking given the young age of these structures," he said. "Lack of such diagonal bracing has caused numerous building failures in the past." Every failed roof characterized by a progressive collapse - in which numerous adjacent bays went down had improperly braced trusses, he said.
Bohnhoff said that continuous lateral bracing was not properly diagonally braced and should not have been used in the first place. Instead, all compression web chords should have been T- or L-braced.