Browsing by Author "Ribeiro, Tiago Pinto"
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- An Additive Manufacturing Suitable Methodology for Topology Optimization of Bolted Structural Joints with Cover-plates in Compliance with Structural EurocodesPublication . Ribeiro, Tiago Pinto; Bernardo, Luís Filipe AlmeidaThe current design of steel connections does not meet the possibilities offered for its fabrication by novel Additive Manufacturing (AM) techniques, both due to calculation methods insufficiency and standards limitations. This leads to building structures that are heavier, less economical, and less sustainable than our industrial capacity allows. While AM has been employed for rapid prototyping mostly in automotive, materials design, medical devices and aerospace industries through the past twenty years and Topology Optimization (TO) has gained momentum since the 1990s, the fact is that the lack of a comprehensive set of boundaries and methodology has limited its use to product development, rather than widespread, scalable, safe and standardised use in construction. Currently, while we already have good software for TO, which can assist in developing structural solutions whose added value justifies its production with AM enterprises, there is not a strong link between optimisation, mass fabrication and safety checking. We design to optimise weight, strength, and stiffness, not fully facilitate fabrication, comply with codes or use the best options given by AM. The lack of methodologies and guidelines prevents civil and structural engineering from embracing TO and AM. To address the meagre use of TO in the civil engineering industry, this research programme allowed to develop a methodology which accounts for i) the TO capabilities and software, ii) AM fabrication practical requirements and problems, iii) code requirements, iv) structural safety and performance goals to enable and foster the TO and AM to structural steel joints. Specifically, this was focused on bolted joints with cover plates in steel beams, designed to the current European standards, as joints are essential in steel structures, contributing up to 25% of the global weight and concentrating the complexity in design and, therefore, the industry’s added value. The novel code-compliant methodology was proposed, validated with non-linear Finite Element Analyses (NLFEA) and applied to several parts of a typical bolted joint. Through the research programme, successive methodology developments were made to account for different loading and buckling phenomena. For the cover flange plate under tension, it has been found that a 50% volume reduction is possible by employing linear elastic TO and establishing the non-exceedance of the steel ultimate stress as a criterion. NLFEA showed that if the original joint capacity is to be maintained, the maximum optimisation threshold reduces only 45% of the initial volume. For the cover-plate under compression, the initial volume can be decreased by up to 40% while maintaining the connection’s original capacity and that a 30% volume decrease may be achieved while maintaining the original plate capacity. In both cases, the plate’s ultimate deformation capacity was enhanced. Furthermore, for web plates subjected to shear forces, results show that reducing up to 87.5% of the plate’s initial volume is possible while keeping the connection’s original capacity. Also, it has been found that the initial volume can be reduced up to 20% without affecting the original plate capacity and up to 60% while ensuring that the ultimate plastic displacement is larger than that of the original plate. Further developments allowed employing state-of-the-art optimisation techniques, namely the Non-penalisation Smooth-Edged Material Distribution for Optimising Topology (np-SEMDOT) algorithm and assess both the added value and practicality of using it in the proposed code-compliant methodology, instead of broad-use software packages. Ultimately, laboratory testing was endeavoured to evaluate the numerical investigation results, allowing the validation of the former. Two critical conclusions that emerged from this work are that linear elastic TO could not meet the safety needs and that the introduced validation stage with NLFEA is an essential step, highlighting the novelty and significance of the proposed method. Topologically optimised solutions showed a significant volume and cost reduction, meaningfully contributing to the steel construction decarbonisation goals and leading to joints with more ductile behaviour.