Civil Engineering researchers discuss modification to the test configuration.
Reinforcing Steel: Advancing Seismic Resilience
By Mike Emery
Seismic forces originating deep within the Earth constantly threaten structures. Each year, an average of 600 structures in the United States are damaged by seismic events, resulting in billions of dollars in repair costs. Buildings, bridges and infrastructure can suffer significant damage – cracked foundations, collapsed walls, and caved-in roofs – depending on their design, materials and construction methods. Older buildings not retrofitted or originally designed to resist seismic forces are at greater risk during major earthquakes.
At the Grady E. Harvell Civil Engineering Research and Education Center, known by its acronym CEREC, researchers are working on projects that could lead to the development of stronger and safer structures. One such research project focuses on developing comprehensive design guidelines for steel buildings having special moment frame connections with severe skews. Moment frames are created by connecting beams and columns together in a way that can resist lateral loads created by earthquakes or winds. A skewed moment frame is one where the beams connect to the columns at skewed angles, deviating from a typical 90-degree arrangement. In seismic design, moment frame connection regions are carefully engineered to dissipate the large forces that result from earthquakes.
Under the direction of Gary Prinz, director of CEREC, this project aims to understand the complex interactions between skewed frame geometry and large lateral seismic demands, with a particular focus on connection ductility and deformation behavior – the behavior between beams and columns under large seismic demands. The goal is to create detailed design guidelines within existing seismic provisions, offering engineers a clear path when accommodating skew in special moment frames.
Beyond structural and economic damage, earthquakes pose a serious risk to human life, particularly in densely populated areas. Collapsed structures can trap or injure occupants, complicating rescue efforts.
“As engineers, our top priority is always safety,” Prinz emphasized. “Through projects like this, we can better understand complex structural behaviors and move forward with confidence in our designs.”
He added, “Architectural constraints often arise in the design of steel buildings, challenging structural design approaches. In high seismic areas, steel special moment-resisting frames are popular because they offer brace-free spaces that accommodate many architectural features. However, when moment frames are required to conform to some architectural features, skew may occur at the beam-to-column connections. Current design procedures for special moment-resisting frame connections do not consider skew, and it’s unclear how to manage the demands that may arise from it.”
To address these challenges, faculty and student researchers are conducting full-scale testing of seismic connections under carefully selected loads to replicate severe seismic demands. The facilities and equipment at CEREC enable civil engineering students to gain real-world experience by fabricating large steel assemblies and applying substantial forces – ranging into the hundreds of thousands of pounds – using controlled hydraulic actuators.
As with any research, unexpected findings can alter the course of the project. This project is no exception. Early tests revealed unexpected column torsional/twisting effects during the process of applying the large forces. This prompted the team to revise its experimental design and focus on more complex double-sided moment connections having composite concrete slabs. Common in buildings, composite slabs are created when the concrete slab and steel framing are connected in such a way that they work together to resist the applied loads. This required redesigning the testing setup and fabricating new specimens, with valuable support from fabrication partners W & W | Afco Steel.
The research team’s findings are already making a significant impact. Their work on skewed special moment frame connections contributed to commentary guidance in the American National Standard ANSI/AISC 358-16, “Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications.” The ongoing experimental work is expected to further enhance the Seismic Design Provisions in ANSI/AISC 341, providing more comprehensive guidelines for engineers.
Setup for the full-scale special moment frame testing at the Grady E. Harvell Civil Engineering Research and Education Center.