An experimental investigation to assess the major-axis flexural behaviour of 10 hot-rolled steel I-section
beams, strengthened by the addition of material through wire arc additive manufacturing (WAAM) and tested
under either four-point or three-point bending conditions, is presented in this study. The ability of WAAM to
pre-camber hot-rolled steel I-section beams, as well as to enhance their bending moment resistance and initial
elastic stiffness, has been demonstrated. The geometry of the strengthened beam specimens, including the
initial imperfections and pre-camber, were obtained by means of 3D laser scanning. Complementary material
testing was conducted to obtain the mechanical properties of both the hot-rolled and WAAM steel under
monotonic tensile loading. The experimental results showed that significant pre-cambers of approximately
1/200 of the span of the beam could be achieved with only a 2.6% increase in mass. Moreover, increases
of between 11.5% and 33.2% in the ultimate bending moment resistance, and increases of between 8.7%
and 35.9% in the initial stiffness, were achieved for increases in mass of between just 2.6% and 12.3%. The
presented WAAM-strengthening approach can be employed for the strengthening, repair and retrofitting
of steel beams in service, as well as for the fabrication of hybrid steel members with improved flexural
behaviour in new structures.