In engineering as in life, a problem is only a problem if you see it that way. Local buckling in particular can be more of an asset than a burden with the right understanding, Benjamin W. Schafer, PE, PhD, said in the 2024 T.R. Higgins Lectureship Award lecture, “Think Global, Buckle Local: Exploring Local Buckling in Structural Steel,” at NASCC: The Steel Conference.
Observed as far back as the mid-19th century, local buckling is a phenomenon that causes wrinkles, puckers, and, as Scottish civil engineer William Fairbairn described in his 1846 bending tests, “hummocks,” in plates. These tests and the other early observations of steel’s behavior under various conditions of stress paved the way for industry-wide code that has helped engineers predict and control local buckling.
Schafer, who has centered much of his research on local buckling, admits that engineers aren’t necessarily keen on embracing the phenomenon--and, in fact, they often take the route of eliminating local buckling because it simplifies material behavior, avoids deformation, and increases durability for the structures in question.
He asked engineers to take a new look at local buckling as a means to minimize member size while allowing for controlled deformation, even if it means there is more complex behavior involved. “Was it too complicated when I looked at that plate,” he urged them to ask themselves, “or can I use that to my advantage?”
Schafer discussed the mathematics and mechanics of local buckling by examining the evolution of width-to-thickness ratios published in AISC 360 throughout the past century, pointing out that the ratios have gotten more and more complex with new research. Despite the complexity involved in predicting sites of local buckling, Schafer pointed out a key factor that can simplify the calculations: slenderness.
“Getting local slenderness right is a huge ‘unlock,’” Schafer said. “Instead of having huge tables, we can look at two values.”
Two separate paths--eliminating or embracing local buckling--are a historic precedent, but Schafer believes that modern tools and design methods enable engineers to find a middle ground. “There’s no real reason why anyone shouldn’t be allowed to use all the tools,” he said. “With this unlock of local buckling and modern design methods, you get to use both paths.”
This knowledge is vital for the understanding it imparts on the industry, but Schafer discussed the global goals it will also help the industry accomplish. Citing David Billington, who studied structural excellence, he pointed to society’s modern structural needs as perhaps the greatest benefactor of local buckling understanding.
“We’re not in a situation where we can afford to keep putting ‘more’ into the world,” Schafer said. “As we look to the future, where advanced high-strength structural steels are more common and every designer is pressed to maximize sustainability and minimize the thickness of the steel they employ, the importance of mastering local buckling is only growing.”
Local buckling as a social solution rather than a structural problem is a new perspective to take, but one that can shape the future of structural engineering. Schafer discussed how an engineer’s technical depth is a strength, but one must not be afraid of applying that strength to issues of increasing breadth, including sustainability and resiliency in structures.
“I challenge each of you to take your technical depth--for me, that’s local buckling--and apply it widely to see what you can make better,” Schafer said. “Our modern social needs combined with our scientific knowledge provides an opportunity for a new era of structural engineering excellence.”