School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

Evaluation of large-format wire arc additive manufacturing (WAAM) for structural engineering applications

By Hannah D. Kessler

Advisor:

Dr. Ryan Sherman

Committee Members:  Dr. Lauren Stewart (CEE)

Dr. Emily Sanders (ME)

Dr. T. Russell Gentry (ARCH/CEE)

Dr. Edvard Bruun (CEE)

Date and Time:  November 14th, 2025.  8:30 AM EST

Location: Mason 5134

Zoom Meeting ID: 982 8428 3746

Wire arc additive manufacturing (WAAM), a large-format method for “3D printing” metals, presents a transformative opportunity for structural steel fabrication, offering advantages such as geometric flexibility, automation, and enhanced sustainability. However, its adoption in structural engineering is currently limited by the absence of standardized qualification and design procedures. This dissertation addresses critical gaps in understanding WAAM mild steel behavior through a comprehensive experimental program and a literature synthesis, aimed at supporting the development of such procedures.
ER70S-6 is a commonly used welding wire feedstock compatible with ASTM A992 and ASTM A709 Grade 50 steels, grades commonly used in building and bridge construction. ER80S-Ni1 is a welding wire feedstock with inherent corrosion

resistance which is compatible with ASTM A709 Grade 50W steel, a corrosion-resistant grade commonly used in bridge construction. The research focuses on characterizing the material properties, fatigue performance, and bolted connection behavior for WAAM ER70S-6 and ER80S-Ni1 fabricated using a variety of process parameters.
The experimental program included:
• Material Property Characterization – 125 tensile tests and over 150 Charpy V-notch impact tests on WAAM ER70S06 and ER80S-Ni1 specimens to evaluate material properties, presence of anisotropy, and the impact of manufacturing process parameters.
• Fatigue Performance – 56 fatigue tests on both as-built and machined surface finishes to determine fatigue life and classify WAAM ER70S-6 and ER80S-Ni1 steels within American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications fatigue detail categories.
• Connection Testing – 48 WAAM ER70S-6 bolted connection specimens with one- and two-bolt configurations were tested to investigate the failure modes and compare to the measured strengths to specification predictions of the American Institute of Steel Construction’s (AISC) Specification for Structural Steel Buildings for rolled steel. Tests targeted tearout, net section rupture, bearing, and block shear failure modes.
Results showed that yield and ultimate stress were generally isotropic, while ductility and impact energy varied with orientation with respect to the layers. When the slope of regressions to the fatigue data was fixed to match the AASHTO LRFD Specification, the as-built surface finish was Category D and the machined surface finish was Category A. Bolted connections exhibited isotropic strength but orientation-dependent failure modes, including end-splitting, a failure mode not currently addressed by the AISC Specification.
Comparison with existing standards revealed that WAAM mild steel components often met ductility and impact requirements of the American Welding Society (AWS) standards and the AASHTO LRFD Bridge Specification but inconsistently satisfied ultimate stress criteria. Design specifications conservatively predicted connection strength for 30 of 48 specimens but frequently misidentified the governing failure modes. These findings suggest a need for WAAM-specific classification and design provisions.
Ultimately, this dissertation provides foundational knowledge for the development of qualification procedures and design guidelines tailored to WAAM structural components, advancing their safe integration into mainstream building and bridge structures.