This project investigates the use of stainless steel I-sections and shear studs in steel-concrete composite bridges. Bridge structures present many challenges to contractors and structural designers owing to harsh environments, large/variable structural loading and limited access to the sites in which they are often located. Construction and maintenance of these structures can be timely and expensive, particularly in environments where salt and water are present. Unfortunately, on some occasions in the past such as the Mianus River Bridge in Connecticut, corrosion of certain elements in bridges has led to structural collapse and loss of life. Steel-concrete composite beams, comprising a steel I-section connected to a concrete slab by shear connectors, are widely used in buildings and bridges since this system optimises the use of each material and enables beams to span long distances unsupported. However, most research to date has focussed on carbon steel in these applications. Stainless steel has been traditionally less popular owing to its higher material cost and limited available design guidance. Researchers have also increasingly turned their attention to this material in recent years, leading to a better understanding of its structural properties and performance. Stainless steel offers many advantages over carbon steel, most notably superior corrosion resistance. This reduces the need for bridge maintenance and so the higher material cost is compensated for by lower life-cycle costs. This improved corrosion resistance also reduces the likelihood of structural failure. The aim of this research project is to conduct a series of laboratory experiments (push-out tests and full member bending tests) on stainless steel-concrete composite specimens using stainless steel I-sections and shear studs in order to assess the performance of stainless steel. The experiments will be conducted in the strong floor in the structural engineering laboratory of the University of Bradford. Comparisons will be drawn between the performance of stainless steel and carbon steel components. Different types of shear stud will also be compared - welded and bolted/demountable. The demountable shear studs offer further potential advantages with regard to ease of construction/dismantling and a potentially better performance under fatigue loading than welded studs. Following the experiments, numerical models will be developed using finite element software in order to extend the results of the research and enable parametric studies. The results will eventually be used to develop guidelines for incorporation into Eurocode 4, promoting the exploitation of stainless steel to provide safer, cost-effective and lower maintenance steel-concrete composite structures.

Owing to its unique combination of excellent corrosion resistance, low maintenance requirements and high performance in fire and under impact loading, stainless steel manifests itself an appropriate and advantageous construction material for projects where corrosion resistance, durability, maintenance costs or resistance to fire or extreme loading are of importance. Stainless steel is also highly recyclable and reusable, making it a sustainable construction material. Traditionally, due to its initial high material cost, stainless steel has been regarded as an option limited to specialist and prestige applications. However, with increased awareness on whole life-cycle costing and sustainability, rather than simply initial expenditure, the use of stainless steel in the construction and offshore industries has been increasing. At elevated temperatures, stainless steel displays higher strength and stiffness retention relative to carbon steel with different material stress-strain response, leading to considerably enhanced structural performance for stainless steel structural elements relative to those made of carbon steel in fire. However, thus far, this high performance of stainless steel structural elements in fire has been neither scientifically well explored, nor has a design guidance leading to its efficient exploitation been developed. In fact, the current British and European structural steel fire design standard Eurocode 3 Part 1.2 recommends the design methods originally developed for carbon steel members for the fire design of stainless steel structural members. This unsurprisingly leads to very inaccurate estimations of the response of stainless steel structures in fire, precluding the efficient use of their high performance at elevated temperatures by structural engineers in practice. For projects where thermal protection is not used to showcase the attractive appearance of stainless steel, inefficient fire design rules, which may govern cross-section sizes, lead to excessive material use and thus very uneconomic solutions. With the aim of achieving a step-change in understanding the response of stainless steel structural elements at elevated temperatures and in their fire design, the proposed research will involve comprehensive numerical studies on the behaviour of stainless steel structural elements in fire and lead to the development of statistically validated design guidance able to exploit the high performance of stainless steel structures at elevated temperatures. The proposed research will not only consider structural elements made of traditional stainless steel grades but also those made of a number of novel, cost-effective and high performance stainless steel grades recently introduced into the market for structural engineering applications; for the first time, elevated temperature material tests will be carried out on these stainless steel grades in this project. Possessing a number of novel aspects such as involving the first comprehensive investigations on the response of stainless steel plates, sections, columns and beams in fire and the elevated temperature material tests on new stainless steel grades whose elevated temperature material properties are unknown, it is envisaged that the proposed project will fill an important gap of knowledge with respect to the behaviour and design of stainless steel structures in fire. In this project, all the design guidance will be prepared adopting the Eurocode 3 Part 1.2 philosophy; it is anticipated that the project will generate design methods suitable for incorporation into the future versions of Eurocode 3 Part 1.2.

Key to the survival of a building subjected to extreme loads, such as fire, blast and impact is the provision of a robust structural frame, which can accommodate the resulting high strength and ductility demands. To this end, the performance of the beam-to-column joints is paramount, since these will be subjected to high rotation capacity demands and high tying forces, as they are required to facilitate catenary action and provide an alternative load path in the case of a sudden failure of a supporting column. The fundamental hypothesis underpinning this research project is that replacing the carbon steel components in critical parts of the joints (e.g. bolts, angle cleats, plates) with an appropriate grade of stainless steel, which has greater ductility, as well as better fire behaviour, will enhance the joint strength and ductility thus maximizing the resistance to a progressive collapse during an extreme event such as an impact, blast or fire. The project consists of 4 technical work packages with a fifth one dedicated to impact and dissemination, as outlined hereafter: WP 1 focuses on the behaviour of joints under impact loading. Stainless steel plate, bolt and weld material coupons will be tested under high strain rates to determine the material response under conditions brought about by impact loading. The obtained results will be utilised to calibrate material models explicitly accounting for strain rate sensitivity as well as fracture models considering the effect of strain rate and stress triaxiality. Furthermore, lap joints and T-stubs will be tested at high strain rates and FE models will be developed and utilised in parametric studies WP2 studies the behaviour of material and connections at and after exposure to high temperatures ranging from 20 to 1000 degrees centigrade. Isothermal and anisothermal material coupon tests will be conducted on plate, weld and bolt material, whilst for the post fire condition, both air cooling and quenching will be considered. Upon determining the effect of temperature on material response, advanced FE models will be developed to establish the performance of double web cleat, top and seat angle cleat and extended endplate joints under and post fire conditions. WP3 investigates the behaviour of individual joints under moment and shear and double sided joints under moment, shear and tension under static and dynamic loading conditions. Both physical tests and numerical models (utilising the findings of WP1) will be generated to characterise the joint response under realistic column loss scenarios. Supplementary numerical studies on geometrically identical conventional steel joints will also be conducted to compare the performance of the novel hybrid carbon/stainless steel and conventional steel joints. WP4 will utilise all previous WPs to develop and calibrate spring joint models suitable for incorporation into FE simulations of frames using beam elements. Using OpenSees, low-, medium- and high-rise 3D steel frames employing the novel hybrid joints as well as conventional ones will be analysed under a variety of extreme hazard scenaria including impact and fire using a probabilistic approach for the variability in material, geometry and loading. The obtained results will be utilised to determine the probability of failure and derive analytical fragility curves and quantify the effect of the adoption of the novel connections on the survivability of steel framed structures. Finally, WP5 will utilise all previous WPs to develop and disseminate design guidance to maximise the impact of the research. The close collaboration with leading consultants and strong links with BSI, as well as the applicants' close familiarity and involvement with Eurocode 3 will guarantee prompt dissemination of the research findings to the relevant practices, institutions and code development bodies.

IMMPETUS (Institute for Microstructural and Mechanical Process Engineering: The University of Sheffield) was founded in 1997 to undertake truly integrated interdisciplinary research across the disciplines of systems, mechanical and metallurgical engineering, addressing key issues in the metals processing industry. Over the last ten years the unique inter-disciplinary research produced by IMMPETUS has secured national and international acclaim for its systems driven approach to process and property optimisation of a wide range of metals process routes. Using systems engineering we target and optimise experiments to develop basic physical metallurgy in specific areas where knowledge is incomplete, to inform model elicitation, testing and validation. For the complex industrial processes we investigate, there is insufficient basic knowledge to construct true through-process physically based models. In order to cover the intractable factors not adequately described by the existing physically based models, we use hybrid models that merge discrete data, knowledge-based and physically-based models in a unique manner to give unprecedented precision in predictive model capability. All the modelling is verified through the use of a world class array of experimental techniques. The proposal comprises 12 projects which have been constructed in conjunction with our industrial collaborators in order to answer the following questions: 1. How do we formulate a 'generic' framework for 'through-process' modelling to achieve 'right first-time' production of metals?2. Which of the metallurgical and thermomechanical variables affect the microstructure and therefore the final properties of metals, but are not yet fully described by existing models?3. How do causalities (deterministic behaviours) as well as uncertainties (heterogeneities, random behaviours) influence the processing and affect the final properties of metals?4. What are the specific modelling strategies 'best' suited for answering 1, 2, and 3 above?5. Using the elicited models in 4, can we identify the achievable properties for a given process route, and what to do if a particular property is not achievable?6. Using 5, how do we optimise the process route?The programme of work is presented as four themes, all of which are inter-dependent and interwoven. PHYSICAL SYSTEMS will be aimed at developing basic physical metallurgical understanding where knowledge is inadequate, in areas including microstructural heterogeneities, and process conditions that are dynamic and non-linear. In MODELLING SYSTEMS, the physical metallurgy, mechanical engineering and systems engineering will be fully integrated, both through the development of new modelling approaches, and the coupling of existing state-of-the-art modelling that in itself produces new methodologies. PROCESS SIMULATION will involve the upscaling of focused laboratory experiments to accurately and completely simulate the relevant industrial process routes and validate them through appropriate mill trials. SYSTEMS OPTIMISATION will act as a powerful vehicle for integrating these themes and via a careful tuning of model structures/parameters will be core to our technology transfer to our will target specific industrial sponsors and to the wider academic community.