Analysis of variance of tensile tests from spiral welded carbon steel tubes

•Thick spiral welded carbon steel tubular members often used in retaining walls.•Tensile tests performed on coupons taken at different orientations from such tubes.•Stress–strain curves characterised according to an accurate algebraic formulation.•Characterised material properties subject to an analysis of variance (ANOVA).•Results support hypothesis that the spiral welded tube may be treated as isotropic. Thick tubular carbon steel members are commonly used in combination with sheet piles in large retaining walls where they provide the necessary bending stiffness. A current international research project aims to provide safe and efficient design rules for such ‘Combitubes’. These tubes are usually manufactured by continuous spiral welding from a carbon steel coil. One of the key concerns is the possible influence of material anisotropy on the bending resistance of the resulting fabricated tube. Standard tensile tests were performed on several specimens extracted from such tubes, exploring the stress–strain behaviour in different orientations relative to the tube axes and the spiral directions. An analysis of variance (ANOVA) was then carried out to compare the mean values of properties deduced from these tests. This short paper offers statistical evidence that supports the view that an isotropic treatment may be acceptable for computational analyses and design of spiral welded steel tubes. It also illustrates how a standard statistical method may be applied to attempt such a validation, even though the data set may be too small for a rigorous statistical verification.