Swiss Federal Laboratories for Materials Science and Technology (Empa) researchers are using Wire Arc Additive Manufacturing to repair fatigue cracks in bridges and steel structures, printing customized metal reinforcements directly onto damaged components rather than replacing them entirely.
The process, known as WAAM, works by feeding a welding wire through a robotic arm that deposits metal layer by layer onto cracked or weakened areas using an electric arc. Unlike conventional welding, which joins components, WAAM builds three-dimensional reinforcements with geometries tailored to the specific stress pattern of each defect, stopping or slowing crack propagation without touching the surrounding structure.
The shape of the reinforcement, not the volume of material added, determines the outcome. In tests conducted in Empa’s construction hall, cracked steel plates fitted with various printed reinforcements were subjected to repeated loading cycles. All reinforced samples outperformed unrepaired control plates, with two-layer stepped geometries proving most effective. In one case, a collaboration between Empa and ETH Zurich extended the service life of damaged steel plates by up to four times.
“The key isn’t to apply as much material as possible,” says Hossein Heydarinouri of Empa’s Structural Engineering laboratory. “The shape is much more important: an optimized geometry distributes stresses in such a way that the propagation of existing cracks is stopped or significantly slowed down.”
The study also flags a risk: poorly chosen geometries can introduce new stress concentrations at the interface between the base material and the printed metal, making precision design essential.
The On-Site Problem
Fatigue cracking is among the most common failure modes in aging steel infrastructure, and targeted reinforcement is far more resource-efficient than full component replacement. But the path from lab to field remains unresolved. WAAM currently runs on large industrial robotic systems that are difficult to transport, and most damaged structural components are embedded within their structures, not easily removed for workshop repair.
“Damaged components are usually installed within the structure,” Heydarinouri notes. “Today, they would have to be taken to a workshop for repair, which isn’t always realistic in practice.”
Mobile and portable robotic systems are in early development, but the research team acknowledges that widespread on-site deployment will require further advances. In the near term, the approach is most practical for accessible components or parts that can be removed during scheduled maintenance.
Beyond Repair: Adaptive Structures
The Empa team is also working on applications that go further than damage remediation. By combining optimized geometries, WAAM, and advanced materials, the researchers are developing metallic elements that absorb energy under extreme loads, deforming deliberately rather than failing, then recovering as much of their original shape as possible. Potential uses include damping components for earthquake-prone bridges, buildings, and industrial installations.
Empa materials scientist Maryam Mohri is investigating how shape memory alloys can be integrated into WAAM-printed components to further extend their adaptive capabilities. Geometries are developed through numerical simulation and validated experimentally before any industrial application.
WAAM as a Repair Tool
Fatigue cracking in steel infrastructure is widespread, but the standard response is costly, disruptive, and often physically impractical for permanently installed structures. As a result, the construction and infrastructure sector has been exploring 3D printing for repair from multiple angles.
In metal repair specifically, Aconity3D’s multi-material welding head for its AconityWIRE system was designed for repair and maintenance workflows, allowing damaged or worn areas to be selectively rebuilt, reinforced, or modified using application-specific materials. The U.S. Army has integrated WAAM into its Metal Working and Machining Shop Set, allowing soldiers to print and machine metal parts on demand, reducing the need to transport large quantities of stock in operational environments.
Beyond metal, researchers at University College London developed an asphalt 3D printer for road cracks and potholes, while Wales-based Cintec used AM to restore the historic Red House government building in Trinidad and Tobago, installing reinforcement anchors of 36.52 meters, claimed to be one of the longest ever inserted into a structure.
Adding to these efforts, Empa’s research focuses on permanent, load-bearing steel components of bridges and frameworks that cannot be removed, where the geometry of the repair, not just the material deposited, determines whether a crack stops or accelerates.
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Featured image shows Researchers aim to repair damaged bridges and other steel structures using metal 3D printing. Photo via Empa.
