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For decades, steel design has relied on established fatigue and fracture frameworks based on stress-range categories, fracture toughness, flaw assumptions, fabrication considerations, and service temperature. These approaches have served the profession well and generally treat fracture as arising from fatigue crack growth or a pre-existing flaw, with material toughness providing protection against unstable failure. Yet not all fractures follow this expected path. This lecture examines two mechanisms that can produce cracking outside traditional fatigue-based expectations and discusses approaches for achieving reliable structural performance. The first is cracking associated with hot-dip galvanizing of welded steel components. Galvanizing introduces large thermal gradients and exposure to molten zinc, creating conditions in which liquid metal assisted cracking (LMAC) may occur in susceptible details. Rather than being driven by cyclic loading or conventional toughness limitations, LMAC results from the interaction of stress, temperature, material condition, and liquid zinc during fabrication. The lecture examines how design, detailing, fabrication, and galvanizing choices influence susceptibility and how risk can be reduced while retaining the durability benefits of galvanizing. The second mechanism is constraint-induced fracture (CIF), in which local geometric constraint elevates stress triaxiality and suppresses plastic deformation, allowing brittle fracture under otherwise nominally ductile conditions. Unlike galvanizing-related cracking, CIF develops in service and is governed primarily by structural detailing and local constraint. Small changes in geometry, including constraint-relief gaps and attachment configurations, can substantially alter fracture behavior.
Together, these topics broaden the conventional view of fracture in steel structures, illustrating how fracture resistance depends not only on fatigue and material toughness, but also on fabrication processes, local geometry, and constraint.
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Caroline Bennett is the Charles E. & Mary Jane Spahr Professor in the Department of Civil, Environmental, and Architectural Engineering (CEAE) at the University of Kansas (KU). She earned her Bachelor of Science and doctorate from the University of Cincinnati, and joined the KU faculty in 2006. She currently serves as Chair of the KU CEAE Department.
Dr. Bennett’s research has addressed some of the most pressing challenges in structural engineering, including fatigue and fracture performance of steel infrastructure, cracking in galvanized structures, constraint-induced fracture in steel bridges, and innovative structural retrofit strategies for a wide range of structures. She has led national projects with the Federal Highway Administration, the National Cooperative Highway Research Program, the U.S. Army Corps of Engineers’ Engineer Research and Development Center, and state Departments of Transportation, delivering solutions that extend the service life of structures and improve infrastructure performance.
Dr. Bennett serves on AISC’s Committee on Research and TC10 Materials and Fabrication Committee. She recently served on AISC’s Game Changer panel. She contributes to the American Iron and Steel Institute (AISI) Steel Bridge Task Force and Transportation Research Board committees, strengthening connections between research and practice. Bennett received AISC’s Special Achievement Award in 2024, AISC’s inaugural Early Career Faculty Award in 2016, and was named the Robert J. Dexter Memorial Lecturer in 2013 by AISI.