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New Generation Design Methods for Stainless Steel Structures

Periodic Reporting for period 2 - New GeneSS (New Generation Design Methods for Stainless Steel Structures)

Reporting period: 2021-09-16 to 2022-09-15

Current structural design methods consider structural systems, such as frames, as a set of independent beams, columns, and connections, with very little consideration for 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, severely limiting the efficiency with which our cities and infrastructures are built. In these uncertain times when societies need to be more resilient and efficient than 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 the Direct Design Methods (DDM), and allow a faster, simpler, safer and more efficient design of structures, but they were not available to structural engineers in the European structural codes until very recently. Thanks to the NewGeneSS project, the DDM has been extended to Europe, and design recommendations have been developed for stainless steel structures to ensure that the safety requirements mandated by policy makers are met through the calibration of safety factors.

This project is a joint effort between the Universitat Politècnica de Catalunya, the University of Sydney and Pedelta S.L. and has built the basis of the next generation of European structural design standards. This will, in turn, encourage innovation and help European design offices to mobilize their whole range of capabilities and assets, strengthening international collaboration and the transfer of knowledge to industry and society.
Because of the many uncertainties that exist in both the resistance of structures and the loads to which these are subjected, the 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.

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, including the assembly of a comprehensive database of more than 12,500 measurements on the geometric and material properties of real stainless steel structures. These deviations from the theoretical properties were then used to evaluate the variability on the final resistance of stainless steel frames through more than 6,000 advanced numerical simulations.

Then 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 were derived. The new direct design method was then applied to real structures with the assistance of practicing structural engineers to test its applicability to daily design praxis, and modifications were proposed to improve its ease of use and consistency. And finally, a set of Pre-normative design recommendations were developed to contribute to the implementation and acceptation of the method, which will be the basis of the next generation of structural design specifications for stainless steel structures internationally.

The results derived from the NewGeneSS project have been disseminated and 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 capable of producing new knowledge as soon as possible. The Project has also made significant efforts to successfully transfer the knowledge gained to society by promoting and spreading the new advanced design methods among professional practitioners and Master’s students through the development of Design Recommendations, workshops, recorded webinars and lectures, enhancing awareness on the benefits of such methods. And finally, the Project has also contributed to bringing science in STEM areas to the general public and especially to young students by organizing scientific communication events and activities at elementary schools.
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. The Project has established a rigorous system reliability framework for the probabilistic analysis of structures in the Eurocode environment, setting the foundations for the next generation of structural design specifications for stainless steel structures in Europe, the US and Australia. It also represents the first effort in the systematic calibration system safety factors for the Eurocodes and establishes a clear working methodology for the analysis of other structure types and materials in the future.

The design of structures using this new approach is much simpler and faster, and the final solutions allow average reductions in material consumption of 16% (and up to 23% in some particular cases), meaning that structures designed with this new method are not only cheaper, but also that the carbon emissions associated to the production of the material that is no longer necessary to build the structure can be avoided. In addition, the new method will allow more consistent structural design approaches across the 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.

In order to contribute to the implementation of these system-based direct design approaches in the next versions of international design specifications, the NewGeneSS project has also delivered a set of Pre-normative design recommendations, which will help practitioners in understanding and applying this new method, and will transfer the knowledge gained in this Project to the industry to harness all the knowledge embodied at European design offices. In this regard, many of the research outcomes derived from this Project are very likely to be incorporated in the relevant Eurocodes and used by practicing engineers on a daily basis, some of which have already been included in Technical Reports to European specifications such as prEN 1993-1-14.
Statistical characterization of stainless steel structures
Developed Pre-normative design recommendations
Advanced numerical simulation of stainless steel portal frames
Reliability analysis of stainless steel portal frames