A new computer model from researchers at the Massachusetts Institute of Technology (MIT) could help bridges and buildings use less material while remaining practical to build. The approach is based on a process known as topology optimization, a computational method that determines the most efficient placement of materials.
The study was led by Josephine Carstensen, a professor of civil engineering at MIT. According to the team, the framework bridges the gap between optimized digital designs and practical construction.
Carstensen believes that the technique could significantly reduce both costs and carbon emissions. "There's an interplay between the materials you're using, the constructability of designs, and the optimization of the structure," she said. "You need to be able to address all three at the same time. That's what we tried to do here."
A smarter design
Topology optimization uses computer programs to place material where it is most efficient, for example, by building the strongest possible structure at the lightest weight. But it is mostly used in research and 3D printing rather than by engineers constructing bridges and buildings. That's because the designs are often too difficult and expensive to build. They are complex, spider-web-like structures that would challenge even the most capable engineers.
To address the challenge, the MIT team developed a framework that allows users to define practical construction limits from the beginning of the design process. Engineers can specify the maximum number of structural members meeting at a joint, minimum connection angles, and minimum component sizes.
The system supports multiple materials and can combine steel and timber. It selects a single material for every structural part and then checks that all connections are strong enough to meet engineering standards. "You can't have a part that's 72 percent timber and 28 percent steel," said Zane Schemmer, an MIT doctoral student and the study's first author.
From design to reality
To demonstrate the method, the research team redesigned the Lockport "Upside-Down Bridge" near Buffalo, New York. They generated timber-only, steel-only, and timber-steel hybrid truss designs. They then tested how different construction constraints affected the final structures.
The redesigns showed that no single material was best by every measure. "We saw how the system knew that you could design a bridge of pure steel, but that might not be best from a carbon standpoint," Schemmer explained. "Or you could design a bridge out of purely timber, but that might not be the strongest."
Schemmer believes that by strategically combining the materials, the framework can use timber where carbon savings matter most and rely on steel only where additional strength is necessary.
The optimization requires more computing power than some existing methods. However, the research team said it ran its experiments on a standard laptop, suggesting that the framework could be practical for engineering firms.
"This approach has been avoided by industry in the past, but now we think it's a practical way to solve problems dealing with variable constraints," Schemmer concluded.
The research was published in the journal Automation in Construction.