Experimental study on wire and arc additively manufactured steel double-shear bolted connections

Wire and arc additive manufacturing (WAAM) has emerged as a highly promising technique for manufacturing large-scale steel structural elements. However, the distinct mechanical properties of WAAM steel could potentially lead to different performance of WAAM steel bolted connections compared to the traditional steel bolted connections. This study aims to investigate the material properties of WAAM steel and the structural behaviours of WAAM steel bolted connections, focusing on the effects of print layer orientation and connection plate geometrical dimensions. A total number of 24 WAAM steel coupon specimens with three different print layer orientations and 36 WAAM double-shear bolted connections with two print layer orientations and different geometric dimensions were designed, fabricated and tested under monotonic tension. These specimens were measured using a 3D laser scanner and Digital Image Correlation (DIC) was adopted to measure the structural response during testing. The impact of print layer orientations on WAAM material properties and the effects of WAAM material properties on bolted connections were analysed and discussed. The current design codes for traditional steel bolted connections were evaluated against the test results of WAAM steel bolted connections. The study found that the print layer orientations of WAAM steel plates initiated an anisotropic material property of the coupon specimens, demonstrated by the differences in ultimate tensile strength and strain of specimens with different print layer orientations. Five failure modes, including net section tension, shear-out, bearing, end-splitting, and block shear failure were observed for the bolted connections. The material anisotropy further affects the performance of the bolted connections, though in the same dimensions, 28% of the specimens presented different failure modes due to the different print layer orientations. The effectiveness of current steel design standards was compromised by inaccurate predictions of failure modes due to the distinct end-splitting failure mode and the effects of material anisotropy, though the predictions of the ultimate capacities of the WAAM lap shear specimens were relatively accurate.