Laboratory

This project investigated the structural performance of optimised steel trusses fabricated using wire arc additive manufacturing (WAAM), demonstrating the potential of combining WAAM and optimisation methods to produce efficient, large-scale structural elements. 

Led by: Professor Leroy Gardner (PI) and Dr Pinelopi Kyvelou, with Athina Spinasa

Industrial partner: MX3D

The Challenge 

To assess whether optimised steel trusses produced via WAAM can achieve high structural efficiency and reliability comparable to or exceeding conventional hot-rolled steel trusses. 

Our Approach 

Six 2 m-long optimised trusses (i.e. cantilever, propped cantilever and simply supported configurations) were fabricated by MX3D using a six-axis robotic WAAM system. At Imperial’s Structures Laboratory, material tests, 3D laser scanning and full-scale bending tests using digital image correlation (DIC) were conducted. Complementary finite element simulations were developed to compare and validate results. 

Outcome

The WAAM trusses achieved up to 95% higher capacity-to-mass ratios than equivalent conventional steel designs. The study demonstrated the feasibility of printing large-scale, structurally optimised steel components with significant efficiency gains, supporting the adoption of WAAM in the construction sector. 

Project images

Facilities used

All testing and analysis was conducted in the Structures Testing Lab using a suite of cutting-edge experimental and analytical facilities.

• Advanced 250 kN and 500 kN Instron testing machines enabled precise control and measurement of both material and full-scale structural tests.
• A high-resolution FARO ScanArm with integrated laser line probe provided rapid and ultra-accurate 3D geometric measurements of the printed trusses.
• A four-camera LaVision digital image correlation (DIC) system delivered full-field, non-contact strain and displacement data with exceptional spatial accuracy.
• A bespoke large-scale test rig, incorporating a hydraulic actuator and adjustable boundary conditions, allowed realistic simulation of different support configurations.
• Finite element simulations were performed using ABAQUS, one of the most advanced commercial FE packages, to complement and validate the experimental results.

Together, these state-of-the-art facilities provided a comprehensive experimental environment capable of capturing the complex behaviour of 3D-printed steel structures with unprecedented precision.

While classical energy absorption systems rely on permanent material damage to absorb mechanical energy, this renders such systems to be single-use. By mobilizing structural instability (elastic buckling) as the mechanism for absorbing energy, its reversibility makes the potential development of multi-use systems feasible. The present work investigates thin lattice structures where tuning of the internal structural elements can affect their characteristic post-buckling response such that they may become suitable for absorption applications.

Led by: Professor Ahmer Wadee, Dr Andrew Phillips, and Dr Anton Köllner (PIs), with Dr Adam Bekele and Yuhang Liu

The Challenge 

Energy absorption systems are used to shield structures from dynamic loads such as impact or explosions. The technical challenge lies in replicating the “high strength–low stiffness” mechanical response that is ideal to absorb a significant amount of energy while providing protection from stress propagation. Once mobilized, single-use energy absorption systems can lead to increased structural vulnerability to further events. The use of reversible systems can allow either rapid repair or reuse of such systems for future events or for repetitive loading applications. 

Our Approach 

We use a combination of analytical, numerical and experimental methods based on minimum energy principles to formulate the governing equations, the use of numerical continuation or “generalized path-following” routines to pinpoint and track bifurcations alongside determining the resulting mechanical responses. We then use with nonlinear finite element analysis within ABAQUS for verification and validate against small-scale experiments with specimens made from additive manufacturing (3D printing).

Outcome

While this is on-going work, key findings have included that triggering instabilities in a controlled sequence within a lattice can provide the desired response albeit with a combination of buckling and permanent deformation.

Project images

Experiments on 3D printed lattices

Facilities used

All testing and analysis was conducted in the Structures Testing Lab using a suite of cutting-edge experimental and analytical facilities.

• Advanced 100 kN Instron testing machines enabled precise control and measurement of both unit cell and and full lattice tests.
• Analysis was conducted either using existing numerical continuation codes such as AUTO or a bespoke code developed within the symbolic computation system, Mathematica, by Dr Köllner (DOI: 1016/j.cma.2024.117704)
• Finite element simulations were performed using ABAQUS, one of the most advanced commercial FE packages, to complement and validate the experimental results.

Related publications

• MA Wadee, A Köllner, L Lapira (2025). Analytical modelling of structural instabilities: Recent developments and outlook. In: A Zingoni, “Engineering materials, structures, systems and methods for a more sustainable future”, pp. 3–10. Keynote lecture at the 9^th International Conference on Structural Engineering, Mechanics and Computation (SEMC 2025).
• A Bekele, MA Wadee, ATM Phillips (2023). Enhancing energy absorption through sequential instabilities in mechanical metamaterials. Royal Society Open Science, 10:230762. DOI: 10.1098/rsos.230762
• MA Wadee, ATM Phillips, A Bekele (2020). Effects of disruptive inclusions in sandwich core lattices to enhance energy absorbency and structural isolation performance. Frontiers in Materials, 7, article 134. DOI: 10.3389/fmats.2020.00134

The versatility of Wire arc additive manufacturing (WAAM), a type of metal 3D printing presents opportunities for strengthening of steel structures. The heat input provided by the 3D printing process can in fact enhance the structural performance, not only by the simple addition of structural material but also by pre-cambering. In controlled tests on beams, we have found that we can achieve a disproportionate increase in strength for only a small increase in material volume.

Led by: Professor Ahmer Wadee,  Professor Leroy Garner (PIs), and Dr Pinelopi Kyvelou, with Jiachi Yang

Industry partner: Steelo Ltd

The Challenge 

Curtailing the increase in global carbon emissions from the construction sector demands that civil engineering structures become far more materially and structurally efficient, durable over a long time and are able to withstand increasing strength requirements over time. Metal 3D printing provides multi-faceted opportunities in addressing these challenges and this project focuses on strengthening steel structures through 3D printing where the joint actions of targeted material additions and thermally-induced pre-cambering can introduce a disproportionate increase in strength.

Our Approach 

We use a combination of physical full-scale testing in the Structures Laboratory of a series of steel I-section beams strengthened using WAAM, the use of laser scanning (using FARO ScanArm) and digital image correlation (4-camera LaVision system), alongside sophisticated nonlinear finite element analysis to assess the material, cross-section and member-level behaviour to structural failure.

Outcome

We have demonstrated that the effect of the 3D printing process through WAAM provides significant changes in residual stresses and geometry that in combination can lead to a disproportionate increase in structural capacity. This has potentially very positive consequences for existing structures that require strengthening.

Project images

Experimental setup for strengthened beams

Facilities used

All testing and analysis was conducted in the Structures Testing Lab using a suite of cutting-edge experimental and analytical facilities.

• Advanced 250 kN and 500 kN Instron testing machines enabled precise control and measurement of both material and full-scale structural tests.
• A high-resolution FARO ScanArm with integrated laser line probe provided rapid and ultra-accurate 3D geometric measurements of the strengthened steel I-beams.
• A four-camera LaVision digital image correlation (DIC) system delivered full-field, non-contact strain and displacement data with exceptional spatial precision.
• A bespoke large-scale test rig, incorporating a hydraulic actuator and adjustable boundary conditions, allowed realistic simulation of different support configurations.
• Finite element simulations were performed using ABAQUS, one of the most advanced commercial FE packages, to complement and validate the experimental results.

Together, these state-of-the-art facilities provided a comprehensive experimental environment capable of capturing the complex behaviour of 3D-printed steel structures with unprecedented precision. 

Related publications

• J Yang, P Kyvelou, MA Wadee, L Gardner (2024). Simulation and prediction of residual stresses in WAAM-strengthened I-sections. Structures, 69:107248. DOI: 10.1016/j.istruc.2024.107248
• J Yang, MA Wadee, L Gardner (2025). Strengthening of steel I-section beams by wire arc additive manufacturing – Concept and experiments. Engineering Structures, 322:119113. DOI: 10.1016/j.engstruct.2024.119113
• J Yang, MA Wadee, L Gardner (2025). Strengthening of hot-rolled S355 steel I-section beams using WAAM high strength steel. Thin-Walled Structures, 215:113437. DOI: 10.1016/j.tws.2025.113437
• J Yang, MA Wadee, L Gardner (2025). Residual stresses in steel I-section beams strengthened by wire arc additive manufacturing. Journal of Constructional Steel Research, 232:109606. DOI: 10.1016/j.jcsr.2025.109606