Design strength parameters of dot-by-dot Wire-and-Arc Additively Manufactured stainless steel bars

Wire-and-Arc Additive Manufacturing (WAAM) is a promising solution to build a new generation of efficient steel structures with reduced material use. The dot-by-dot printing strategy enables to manufacture complex lattice steel structures such as diagrid elements and rebars for free-form reinforced concrete elements. Their structural application requires reliable design procedure for the full exploitation of WAAM in Architecture, Engineering and Construction (AEC) industry. The present study focuses on the calibration of design strength parameters of dot-by-dot WAAM-produced 304 L stainless steel straight bars based on the results of tensile tests performed on batches of specimens produced with different build angles (i.e. 0°, 10° and 45°). The results are then grouped into samples, the first three samples corresponding to the individual batches of specimens produced with the different build angles (i.e. 0°, 10° and 45°), to assess the influence of the printing inclination on the mechanical response, while the fourth sample merging the specimens produced at 0° and 10° to account for the effect of the sample size in a statistical way. The calibrated characteristic and ultimate limit state design values (both at yielding and ultimate conditions) and corresponding partial safety factors are evaluated according to the best-fit statistical distributions derived from the experimental test results. Two different approaches are compared to account for the effects of the sample size: one based on Eurocode 0 “design assisted by testing” procedure, and one based on the estimation of the confidence interval of both the 5 % and 0.1 % percentiles (corresponding to the characteristic and ultimate limit state design values). Additional considerations are also made on the strength hardening ratio. The results indicate that, for the investigated dot-by-dot WAAM process, a build angle higher than 10° could have significant effects on the design values and partial safety factors, therefore it should be properly accounted in the structural design stage.