The University of Sheffield
Department of Civil and Structural Engineering

Cross-section Modelling For The Efficient Design Of Structural Members With Non-linear Materials And The Continuous Strength Method

Supervisor: Dr Andrew Liew

Plain carbon steel remains an important structural material in modern construction, due to its competitive cost, high strength and stiffness, and its speed and ease of fabrication with welded or bolted joints. Stainless steels are materials that offer high durability and corrosion resistance, differing in composition than plain carbon steel by the addition of other alloys, leading to a change in the material behaviour with more rounded stress--strain curves. The family of steels find use in construction where durable, long-span, high-rise, lightweight or signature structures are required. Aluminium is another metal that is gaining increased use in construction.

It is important in structural design, that there is a balance between efficient codified rules that engineers will use in the design office, and the accurate modelling of the real structural behaviour taking due account of the material under consideration and its structural role in the building. Unfortunately, structures are being over-designed through current codified guidance and design/analysis tools and methods, and so material is being used in an ineffective and less sustainable manner. As the Eurocode design philosophy is fundamentally overly-conservative, it inhibits an efficient utilisation of cross-section strength. This is because it cannot capture behaviour if the actual cross-section strength is anything other than yield and plastic resistances (for non-slender sections), and severely limits strength gains from materials with significant strain hardening potential.

One alternative design methodology which allows for the use of any material model and continuous resistance functions with respect to cross-section slenderness, is the Continuous Strength Method (CSM). Already very promising results applying the CSM with a bi-linear material model have been made, and it can be seen as an alternative methodology in tackling more efficient member design when compared to Eurocodes. The continuous nature of a CSM design resistance function, compared to the EN 1993-1-1 step-wise classification method, gives improved predictions when compared to test data. The method has so far been developed with highly non-linear materials for predicting cross-section strengths from test results and numerical simulations.

The goal of this research project is to combine the well established Continuous Strength Method, which has proven its effectiveness at taking back some of the excessive conservatism in Eurocode strength predictions, with efficient numerical models including. The research will lead, amongst others, the following important enhancements: 1) integrating new material models that are well-suited at modelling non-linear behaviour, 2) examination and inclusion of residual stresses, strength enhancements and full cross-section element interaction, 3) determination of new design resistance equations based on accurate discretised cross-section models, 4) verification of these models with the latest wide pool of experimental data, and 5) development of opensource tools, to be made available to engineers in practice and to academics for research collaborations.

It is expected that the additional push in this direction will move the CSM onto another level, enabling the modelling of cross-sections over a broad range of materials and manufacturing processes. It will also improve our understanding of structural behaviour, which can lead to more accurate strength predictions in the responsible design of members in construction.

This position is for a PhD student working full-time, after the successful award of a departmental EPSRC Doctoral Training Partnerships (DTP), or through a self-funded / scholarship placement. To apply please send a two-page CV and covering letter to a.liew@sheffield.ac.uk.

This project is NOT FUNDED, although Departmental/University scholarships are available for applicants who can demonstrate strong evidence of research potential.

Pre-requisite qualification

The successful applicant is likely to have a first degree in an engineering discipline (civil, structural, mechanical etc). He/she will also have sound mathematical and computer programming skills, and display an interest in fundamental structural mechanics, design codes and equations, and calibration with experimental test data.