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New Generation Design Methods for Stainless Steel Structures

Periodic Reporting for period 1 - New GeneSS (New Generation Design Methods for Stainless Steel Structures)

Reporting period: 2019-09-16 to 2021-09-15

Current structural design methods consider structural systems, such as frames, as a set of independent beams, columns, and connections, with very little consideration of the interaction between them, and the resistance of each member is checked independently. This design procedure is complex and time consuming, and often underestimates the resistance of structures, thus severely limiting the efficiency with which our cities and infrastructures are built. In these uncertain times in which societies need to be as resilient and efficient as ever, it is fundamental to develop advanced and highly optimised design methods and to use sustainable construction materials such as stainless steel under the consideration of life-cycle cost strategies.

Thanks to recent advances in structural analysis software, it is now possible to accurately predict the behaviour of complex structural systems and to switch to more holistic design methods that consider structures as complete systems in a more integral way. In other words, it is now possible to change the paradigm of structural design. These new methods are known as Direct Design Methods (DDM), and allow a faster, simpler, safer and more efficient design of structures. And the main goal of the NewGeneSS project is to develop DDM design recommendations for stainless steel structures to ensure that the safety requirements mandated by European policy makers are met through the calibration of suitable safety factors.

The project is a joint effort between the Universitat Politècnica de Catalunya, the University of Sydney and Pedelta S.L. and will build the basis of the next generation of European structural design standards. This will, in turn, encourage innovation and will help European design offices to mobilize their whole range of capabilities and assets, strengthening international collaboration and the transfer of knowledge with industry.
Because of the many uncertainties that exist in both the resistance of structures and the loads to which these are subjected, failure of structures is possible. This issue is tackled by prescribing safety factors that guarantee that the probability of failure of structures is that accepted by society as a compromise between safety and economic viability.

While safety factors for the current design methods are prescribed in design standards, they still need to be derived for the new advanced direct design methods being developed at the moment to ensure all safety requirements are met. Research works carried out in the NewGeneSS project focus on the calibration of these safety factors for the advanced design of stainless steel structures. In order to do this, a fundamental step was to fully understand and characterize the variability in the resistance of stainless steel structures and in the loads to which such structures are subjected.
Despite having strict manufacturing tolerances, a certain variability and uncertainty is inevitable in the geometric and material properties of stainless steel structures, which then affects the resistance of the resulting structure. Hence, a comprehensive database with more than 12,500 measurements on real stainless steel structures was assembled on geometric and material properties to characterize the deviations from the theoretical properties. Statistical models were also derived for the different properties.

The effect of the uncertainties observed in these geometric and material properties on the final resistance of stainless steel frames was evaluated using advanced numerical simulations. From more than 6,000 numerical models, the strength of a variety of stainless steel frames subjected to gravity loads and gravity plus wind load combinations was investigated, while information about the variability in the loads was obtained from the literature. Finally, the safety levels corresponding to different safety factors were determined through reliability analysis techniques known as First-Order Reliability Methods. Using these results, recommendations for the safety factors necessary to meet the reliability requirements in different international design standards (European, US and Australian frameworks) were derived.
Research activities carried out in the NewGeneSS project have been communicated to different target audiences, including academic peers, university students, different associations, industry (design offices), and the general public. Results have also been disseminated through high-impact journal publications, international conferences, seminars and social media to ensure they were successfully transferred to society and capable of producing new knowledge as soon as possible.
The work performed in the context of the NewGeneSS project has significantly contributed to the progress beyond the state-of-the-art in different fronts.
A comprehensive set of statistical models describing the variability in material and geometrical properties of stainless steel structures has been proposed for the first time, which will serve as basic input information for future research on structural reliability. In addition, the calibrated safety factors for the design of stainless steel frames using advanced direct design methods also represent the first of their kind, and will very likely be incorporated in the relevant design codes and be used by practicing engineers on a daily basis.

The project has also resulted in the establishment of rigorous reliability frameworks for the probabilistic analysis of structures in the Eurocode environment, which is not limited to stainless steel structures and will be applicable to other structure types or materials in the future.
With the aim of developing design recommendations that will settle the basis for the next generation of Eurocodes, an evidence-based scientific report will be prepared for European policy-makers, which will be indispensable to transfer the knowledge gained in this project to the industry, and to harness all the knowledge embodied at European design offices.

The new design methods will be more consistent across all different international design specifications, enhancing the competitiveness and the presence of European design offices in third countries, encouraging efficiency and innovation, and strengthening international collaboration.
The project has also contributed to the development of long-term strategic alliances between Spain and Australia, helping the beneficiary in the process of becoming an independent researcher through training in a set of research and transverse skills.
Statistical characterization of stainless steel structures
Reliability analysis of stainless steel portal frames