Development of inelastic design procedures for stainless steel indeterminate structures

The excellent atmospheric corrosion resistance and favourable mechanical properties of stainless steel make it well suited for a range of structural applications, particularly in aggressive environments or where durability and low maintenance costs are crucial design criteria. The main disadvantage hindering the more widespread usage of stainless steel in construction is its high material cost and price volatility. However, life-cycle costing and sustainability considerations make stainless steels more attractive when cost is considered over the full life of the project, due to the high potential to recycle or reuse the material at the end of life of the project.

The design of stainless steel structures is covered by a number of international design codes, which have either recently been introduced or or were recently amended in light of recent experimental tests, thus indicating the worldwide interest stainless steel has received in recent years. Despite the absence of a well-defined yield stress, all current design standards for stainless steel adopt an equivalent yield stress and assume bilinear (elastic, perfectly-plastic) behaviour for stainless steel as for carbon steel in an attempt to maintain consistency with traditional carbon steel design guidance.Given the high material cost of stainless steel, improving the efficiency of existing design guidance is warranted. Improvements can be made either by calibrating the existing design procedures, some of which are based on engineering judgment and limited test data, against additional experimental results, or by devising more accurate design approaches in line with actual material response. In any case more efficient yet safe design rules are desirable.

The majority of published research articles on stainless steel structures focus on the response of individual members. Due to insufficient relevant experimental data, no rules are given for plastic global analysis of indeterminate stainless steel structures in any current structural design code, even though the ductility of stainless steel is superior to that of ordinary structural steel. The controversy of not allowing plastic design for an indeterminate structure made of a ductile material is obvious in Eurocode 3:Part 1.4 where it is explicitly stated that "No rules are given for plastic global analysis" even though a slenderness limit for stocky elements is specified in the same code. Moreover, because of the lack of relevant experimental data for stainless steel frames, no specific design provisions to account for second order effects in stainless steel frames are specified in any stainless steel design code. Deficiencies in current design guidance puts stainless steel at a disadvantage compared to other materials thereby hindering its use in applications where it might be the preferred solution, had the design standards not imposed strict restrictions to its design due to a gap in current knowledge.

The proposed project aims at investigating the structural response of stainless steel indeterminate structures and developing appropriate design rules, by means of experimental studies on two-span continuous beams, as well as portal frames and advanced numerical analyses. Experimental results, suitable for the validation of numerical models, will be generated and will allow a rigorous study of the ultimate response of indeterminate stainless steel structures. The accuracy of current design procedures (i.e. not allowing for plastic design or partial moment redistribution in indeterminate structures) will be assessed and the possibility to apply plastic design to stainless steel structures will be explored. It is envisaged that the proposed project will lead to design rules suitable for incorporation in EN 1993: Part 1.4.

This research proposal aims at addressing shortcomings in current stainless steel structural design codes thereby enabling designers to make informed decisions when selecting a structural material for a given project and promoting the use of stainless steel in construction with profound economic and environmental benefits. It is envisaged that the outcomes of the project will enable design code amendments thus rendering Eurocodes the most technically advanced design standards and consolidating the internationally leading position of UK research. The project is expected to generate significant short- and long-term benefits for a number of beneficiaries. These include:

1. The international academic community, which will benefit from both the experimental and numerical results. The results of the project will be reported in detail and allow other aspects of underpin future studies into the robustness of stainless steel structures and structures employing material with a highly nonlinear response.
2. The UK construction industry, which is both a major contributor to UK GDP and also a major contributor to CO2 emissions. As a result of the project, awareness of the benefits of stainless steel in construction will be raised and safe and economic design procedures will be generated. Increased use of stainless steel as a result of more advanced design guidance will be promoted thereby helping the construction industry to reduce its carbon footprint.
3. The PDRA and his/her future employers will significantly benefit from the experience that the PDRA will gain working on the project. The mentor allocated to the PDRA and the whole research environment in the University of Birmingham will nurture a talented researcher enabling him/her to take senior academic or industrial posts in his/her future career.
4. Current and prospective civil engineering students will greatly benefit from the project. Current MEng and MSc students will have the opportunity to engage in research via suitable research projects within the framework of the project. The findings of the research will inform the teaching of relevant structural engineering modules thereby delivering a long-lasting benefit for prospective students and contributing to their training.
5. School children will benefit from the dissemination of project results in university open days and during school visits. The project will serve as a showcase for structural engineering research and practice and can potentially help to raise awareness on the importance of civil/structural engineering and render it an attractive choice for the children's future studies.
6. Finally, the wider society will benefit significantly from the improvement of current design procedures and the promotion of a sustainable material in the construction industry, which will lead to reduced CO2 emissions.