Concrete and hybrid structures
Use of high strength steel in structural applications
High-performance materials are necessary to meet the future demands of the construction industry, which is strongly influenced by a growing population and depletion of natural resources. Sustainable development is central to research and development into innovative structural materials, and requires solutions to be economically viable whilst equally providing a positive contribution towards environmental and social factors. In this context, high strength steels (HSS) have the potential to contribute towards such demands by reducing the weight of structures when employed in appropriate applications. Lighter structures require smaller foundations, shorter transportation and construction times and also lower CO2 emissions.
Brunel is currently heavily involved in research projects looking at the performance of HSS in structural applications. A brief summary of a couple of the projects are included hereafter:
- HSS in steel/concrete composite beams: This work is investigating the feasibility of using HSS in composite beams, which brings potential benefits in terms of reducing the self-weight of the structure and also efficiency in design in that the increased strength of HSS is utilised in the part of the beam which is in tension, so buckling is not an issue. The study is also investigating if current Eurocode design methods (which are intended for normal strength steel) are applicable.
Figure: Image from finite element model of composite beam
- Behaviour of HSS beams in fire: In fire conditions, unprotected steel members experience a loss of strength and stiffness with increasing temperature owing to the rapid temperature development in the structural members which is exacerbated by the high thermal conductivity of steel and high surface area to volume ratio of the section. This work has developed a finite element model using ABAQUS to investigate the resistance of HSS beams (with a yield strength of up to 690 N/mm2) to lateral torsional buckling under fire conditions. The results obtained from the numerical analysis are validated against available test data and then compared with the Eurocode design predictions to assess the applicability of current design specification for laterally unrestrained HSS beams in fire conditions.
Figure: Lateral torsional buckling reduction factors (χLT,fi) with respect to non-dimensional slenderness (λLT,fi) for a range of temperature values.
Tailored energy distributions for laser welding of duplex stainless steel for structural applications
Duplex stainless steel is an excellent material which combines high strength with good corrosion resistance, compared with other grades of stainless steel. It provides a good option for cases where long-term metallurgical stability is required, for example in off-shore and nuclear applications. High power laser welding has recently seen an increase in research interest as it offers both speed and flexibility. The research done by engineers and physicists at Brunel in investigating the important parameters affecting laser welding of duplex stainless steels, with focus on the critical issue of phase balance in the weld region. An extensive experimental programme is currently underway at the NSIRC, coupled with detailed analysis and a review of design guidance for structural applications.
Figure: High powered laser beam welding
Figure: Analysis of the laser beam shape