Laser Cutting Advances Improve Structural Steel Performance

Monday, April 27th, 2015
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Advances in laser cutting technology combined with the growing use of 3D printing could yield significant improvements in the development of structural steel, according to a Virginia Tech professor.

Matthew Eatherton, who worked previously for many years in the earthquake prone state of California, believes there is an opportunity to capitalize on these advancements in water-jet and laser cutting technology in subtractive manufacturing, where material is removed from a structural component, to help steel structures better absorb loads

Using a five-year, $500,000 National Science Foundation CAREER Award, his research shows how steel plates with carefully designed geometric patterns – or voids – cut into them can better withstand both everyday loads and extreme events such as high winds, blasts or shocks from an earthquake than the standard solid steel plates currently used.

“We have a unique opportunity to advance the industry and improve structural steel performance,” said Eatherton.

Structural systems subjected to extreme lateral loads associated with earthquakes, hurricanes or other hazards resist collapse when they can sustain large deformations without breaking. This property, known as ductility, protects the lives of inhabitants because buildings can deform without collapsing.

Typical structural systems that rely on shear deformations in steel plates to develop ductility are challenged by shear buckling and the potential for fracture. Eatherton’s research attempts to revolutionize structural systems that rely on ductile shear deformations.

The innovative approach is to improve ductility and energy dissipation ability by strategically removing material from the plates rather than adding more material. This project will develop cutout patterns, and the underlying science, to convert shear deformations into smaller ductile mechanisms that resist buckling.

The research will include computational modeling and physical experiments, both in reduced scale and full-sized steel components.

The proposed buckling resistant yielding mechanisms have a wide range of potential applications in structural engineering and could be implemented in any structural element that might be subjected to inelastic shear deformations.

Current shear links in cases like a, b, d, and f (shown below) are designed to yield the element in shear. If not detailed carefully and physically tested, elements designed for shear yielding can be prone to fracture because the demands around the perimeter of the plate are high.

Cases like c and g are structural elements that might exhibit buckling when subjected to large loading, such as hurricanes, flooding, impact with wind-borne/waterborne debris or blasts. Buckling can lead to severe loss of ductility or inability to dissipate energy. The buckling resistant mechanisms are expected to prevent buckling and increase fracture resistance in these applications.

Click to enlarge

Click to enlarge

The research also has implications in the continued development of high-rise buildings, especially in earthquake prone areas.

“Many steel seismic force resisting systems that rely on shear deformations (e.g. steel eccentrically braced frames and steel plate shear walls) are currently limited to 160 ft maximum height in high seismic areas unless implemented in conjunction with highly ductile and energy dissipating systems such as special moment frames,” Eatherton said.

“Because the new types of steel shear panels we’re developing dissipate significantly more energy and their non-degrading strength discourages story drift concentrations, it is hoped that the resulting structural systems may be used in taller buildings.”

Eatherton added that his long-term research goal is to fundamentally advance structural engineering design approaches through a marriage of scientific concepts and modern fabrication technology to significantly improve structural performance when subjected to extreme loads.

He is also collaborating with Virginia Tech College of Architecture and Urban Studies to explore the use of exposed geometrically-cut steel plates in building interior designs to serve both structural purposes and architectural form in terms of screening and aesthetics.

“Through our collaboration, we’ve developed a vocabulary to facilitate discussions between architects and engineers,” explained Eatherton. “The architectural form of the plates has been characterized by a set of compositional parameters including scale, visual depth and screening. Using this framework we’ve developed examples of how the walls can satisfy different architectural design objectives.”

Development of the design approaches will take some years in order to test as many configurations and variables as possible before being incorporated into the US Building Codes. Eatherton also stressed the importance of collaboration with the steel industry to facilitate technology transfer and widespread implementation.

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