Efstathios Polydorou

School of Planning Architecture and Civil Engineering
David Keir Building, Stranmillis Rd., BT9 5AG
Room 0G 312B  
Tel  +44 (0)7851620966
epolydorou01@qub.ac.uk      

Education

Master of Engineering with Honours (M.Eng) in Civil & Structural Engineering, First class, The University of Liverpool, UK (2009 – 2013).

Professional qualifications

Member of the Institute of Civil Engineers

Member of the Institute of Structural Engineers

Awards

2013, Lancashire & Cheshire Regional Group Prize

2013, Institution of Structural Engineers Prize

2012, Mott MacDonald Design Prize

PhD Title

Behaviour and modelling of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) under static and dynamic loads.

PhD project Description

The safety and security of infrastructure has become the major concern for the public because of the increasing numbers of natural and man-made disasters such as earthquakes, impacts and blasts resulting in death casualties and damage of structures. Examples include the Oklahoma City bombing attack where 153 out of 175 (87%) people died in the collapsed part of the building and 10 out of 186 (5%) people died in other parts of the building, the September 11 attack where resulted in 2,966 deaths, the Hurricane Katrina with up to 1,833 depths. Beams and slabs are critical elements for the infrastructure and their failure can lead to catastrophic consequences of progressive collapse. The design of structures to resist accidental loads highlighted the interest for improving the resilience of infrastructure using novel materials such as ultra-high performance fibre reinforced concrete with the potential of enhancing the impact energy absorption capacity of structures at high risks.

The term ‘ultra-high performance’ indicates an enhanced combination of UHPFRC material properties such as high compressive and tensile strengths, energy absorption capacity and high stiffness. The enhancement of ductility by incorporating small-sized steel fibres and optimisation of the compacted density of concrete by using fine materials would lead to a viable solution for ultra-high strength fibre concrete. When concrete is subjected in bending, cracks start to propagate with rebar being unable to control the cracks. In contrast, UHPFRC indicates strain hardening after the first crack with the strength of the material to increase until it reaches the ultimate strength. This is mainly due to its homogeneity and inclusion of fibres. Under impact, UHPFRC has the tendency to reduce spalling and scabbing of beams and slabs compared to normal strength concrete. This is mainly attributed to the fact that UHPFRC has the ability to absorb large amounts of energies (fracture energies can be between 20,000 and 40,000 J/m2).

 One of the major challenges for the wider application of the UHPFRC is the difficulties of predicting its dynamic behaviour. The lack of design codes/standards and understanding of the static response of UHPFRC is also limited. The design of a new drop hammer facility to accommodate UHPFRC beam and slab specimens for assessing their impact resistance is one of the challenges of this research. The numerical modelling of the UHPFRC material is also one of the challenges to investigate the strain rate and damage of the material under impact. The strain rate dependency of concrete is of highly importance for explicit nonlinear finite element codes to properly design a structure for all types of loading likely to be encountered during the design lifetime. Validation of the numerical simulations with the experimental results will form the basis for future work to model UHPFRC structural elements subjected to high speed impact projectiles such as rocket propelled grenades (RPGs). Blast engineering consultants who specialise in blast and structural resilience of infrastructure can benefit from the outcome of this project.

Supervisors

Prof. Marios N. Soutsos, Prof. J-F Chen, Dr. D. Robinson

Publications

N/A

Poster(s)/ Presentation(s)

Polydorou, E., Soutsos, M., Chen, J.F., Robinson, D., 2013. ‘Impact and blast resistant structures made with ultra-high performance fibre reinforced concrete (UHPFRC)’. Proceedings of the 16th International IStructE Young Researches Conference, London, pp. 73-74.

Interests

Ultra-high Performance Fibre Reinforced Concrete, Strain hardening cement-based concretes, Mechanical characterisation of ultra - high performance concretes, Non-Linear fracture mechanics, Numerical modelling of materials in particular using ABAQUS, Dynamics of concrete structures, Impact and Blast resistant structures

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