Dynamic testing and analysis of the world’s first metal 3D printed bridge

The MX3D Bridge is the world’s first additively manufactured metal bridge. It is a 10.5 m-span footbridge, and its dynamic response is a key serviceability consideration. The bridge has a flowing, sculptural form and its response to footfall was initially studied using a 3D finite element (FE) model featuring the designed geometry and material properties obtained from coupon tests. The bridge was tested using experimental modal analysis (EMA) and operational modal analysis (OMA) during commissioning prior to installation. The results have shown that the measured vibration response of the bridge under footfall excitation is 200% greater than predictions based on the FE model and contemporary design guidance. The difference between predicted and measured behaviour is attributed to the complexity of the structure, underestimation of the modal mass in the FE model, and the time-variant modal behaviour of the structure under pedestrian footfall. Both OMA and EMA give a dominant natural frequency for the bridge of between 5.19 Hz and 5.32 Hz, higher than the FE model prediction of 4.31 Hz, and average damping estimates across all modes of vibration below 15 Hz of 0.61% and 0.74% respectively, higher than the 0.5% assumed within the design guidance, slightly reducing the peak response factor predicted for the bridge

Structural response of wire arc additively manufactured steel bolted connections under single shear

Anexperimental investigation into the structural performance of wire arc additively manufactured (WAAM) steel single-lap shear bolted connections is presented in this paper. Sixty specimens of different thicknesses, printing strategies and geometric features,including end distances and plate widths,were manufactured using steel wire of a nominal yield strength of 420 MPa and subjected to single shear lap tests. The test results are analysed while the observed failure modes,featuring shear-out, net section tension fracture, end-splitting, localised tearing and curl-bearing failure,are discussed. Digital image correlation (DIC) was used for detailed monitoring and visualisation of the surface strain fields that developed during testing, providing valuable insight into the developed failure mechanisms. The experimental results, which generally followed the anticipated trends, were used to assess the applicability of current design specifications developed for conventional steel bolted connections to WAAM steel bolted connections. It was found that both the cold-formed steel specifications (AISI S100 and AS/NZS 4600) and the structural steel specifications (AISC 360 and EN 1993-1) yield considerable overestimations orunderestimations of the test capacities, depending on the specimen geometry. Further research is underway to underpin the development of improved design provisions

Structural behaviour of composite cold-formed steel systems

The topic of this thesis is the investigation of the structural behaviour of cold-formed steel flooring and purlin systems, taking into consideration the beneficial effect of interaction between structural components. Experiments have been conducted on flooring systems comprising cold-formed steel joists and wood-based particle boards, considering the typical screw fixings employed in current practice as well as alternative means of shear connection. The experimental findings showed that mobilisation of composite action within this type of system, through enhancement, beyond that currently used, of the employed shear connection, is feasible, bringing corresponding increases in capacity and stiffness. In order for the influence of the key parameters to be further examined, a finite element model simulating the examined systems has been developed, validated and employed for parametric studies. Analyses confirmed the experimental findings, showing that significant benefits in terms of capacity and stiffness can be achieved, especially for systems comprising thinner steel sections. Based on the obtained experimental and numerical results, a full design method, following the fundamental concepts of current design codes for composite structures, has been devised, providing accurate predictions of moment capacity and flexural stiffness. Finally, a numerical investigation has been performed on continuous two-span roof systems comprising cold-formed steel purlins, accounting for their interaction with the corrugated sheeting. The study showed that moment redistribution is possible within these systems, but usually accompanied by a reduction of the moment capacity of the central support. A previously devised method for the design of continuous purlin systems, making direct use of cross-section capacities at key locations, together with a factor to allow for the fall-off in moment at the central support, has been assessed and advanced.Open Acces