Design of 3D printed steel structures with improved buckling resistance

: (Alternative Format Thesis)

Abstract

Steel structures typically employ prismatic geometries in the form of lightweight and thin-plated sections due to the feasibility of manufacturing these shapes using traditional techniques. The development of metal additive manufacturing (AM), particularly powder bed fusion (PBF) and wire arc additive manufacturing (WAAM), has enabled the creation of metallic parts with complex geometries, offering the potential to release steel structures form the constraints imposed by conventional fabrication processes. This revolutionary technology has inspired researchers to investigate the use of freeform structural elements, posing a significant challenge to existing design standards.

Advancements in metallurgy leading to the development of higher-strength structural steels and the drive for increasing material efficiency, have promoted the development and the adoption of slender designs. However, these slender structures are particularly susceptible to instability problems under compressive loadings, with local buckling of the plate elements being the dominant concern, restricting the use of structures with very slender plates even their overall cross-sectional areas meet the design requirements. The failures of these thin-walled steel structures can be governed by local buckling in the lowest eigenmode, as characterised by the minimum number of possible buckling waves present in the mode of failure. Higher-order buckling modes, as presented by a greater number of buckling waves at failure and consequently higher buckling resistance, are commonly achieved in a traditional approach by the addition of stiffeners.

This research project proposes an innovative approach employing predefined sinusoidal wavy patterns to achieve higher buckling resistance by delaying the lower buckling modes for minimal increases in material, and thus increasing load-carrying capacity and structural efficiency. The first numerical study has been carried out to investigate various combinations of pre-defined sinusoidal patterns with different amplitudes in stainless steel plates of varying slenderness. Two plate boundary conditions - internal and outstand elements were considered and modelled by employing square hollow section and equal angle section stub columns, respectively. The stiffness, strength, and material consumption were assessed against the typical flat sided structural steel members with the same nominal dimensions, and the effectiveness of different wave patterns and amplitudes were evaluated for a range of slenderness. The experimental validations are then performed on SHS stub columns made by PBF to assess the improvement in structural efficiency and to propose an empirical equation that can predict the behaviour of half-sine wavy patterns.

Built upon these good results, the structural benefit of the proposed stiffening method has been tested on WAAM specimens, as WAAM has been recognised as a preferrable technique in the construction industry. The internal plate elements and the combination of outstand plate elements and internal plate elements have been investigated through SHS and I-sections stub columns made by WAAM. Overall, 17 tensile coupon tests have been carried out to determine the material properties and comprehensive geometric analysis has been performed to assess the manufacturing accuracy. Combined with these findings, 26 stub columns (10 made by PBF and 16 made by WAAM) different wave pattern, slenderness and amplitude have been conducted to assess stability of outstand flanges and internal elements, the applicability of the design codes and the proposed empirical design equation for selective laser melting (SLM) technique.

This research has presented numerical analysis and experimental investigation on both SLM and WAAM made stub columns employing sinusoidal wave patterns to increase their buckling resistances. The numerical and experimental results have indicated a great potential for the innovative patterns being employed to increase the strength of sections with minimal increase in the use of materials.

Date of Award	12 Nov 2025
Original language	English
Awarding Institution	University of Bath
Supervisor	Mark Evernden (Supervisor), Alejandro Jimenez Rios (Supervisor), Jie Wang (Supervisor) & Joseph Flynn (Supervisor)