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Title: Structural behaviour of ultra high performance fibre reinforced concrete slabs
Author: Mahmud, G. H.
ISNI:       0000 0004 6422 1339
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2015
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This study presents an experimental and numerical contribution to the understanding of the structural behaviour of slabs and beams made of ultra-high performance fibre-reinforced concrete (UHPFRC). One of the main factors affecting the use of UHPFRC in major construction projects is not having an accepted design method due to the lack of understanding of the structural behaviour of this material, especially for slabs. Therefore, a major part of this thesis focuses on the static flexural behaviour of slabs. A novel experimental technique is developed and employed within an extensive series of experiments to better understand the structural behaviour of UHPFRC. Tests are conducted on one-way and two-way slabs with both fully fixed (FF) and simply supported (SS) boundary conditions; these are of interest in structural applications such as bridge decks and the floors of buildings. Details of tests conducted on 660 mm square slabs with thicknesses of 25, 35, 45 and 60 mm are presented. The effect of geometries on steel fibre distribution in the UHPFRC specimens was investigated using physical fibre counting at the location of the cracks. It was found that the fibre distribution and orientation changes as the specimen size changes. Moreover, the number of fibres that bridged between the two cracked faces reduced as the specimen thickness increased. A numerical model using advanced finite element modelling techniques in ABAQUS is also presented. A nonlinear concrete damage plasticity (CDP) model is used for the simulation and it was found to agree well with the experimental results in terms of load-displacement behaviour of statically indeterminate UHPFRC slabs. In addition, the model was also found to accurately capture the peak-load carrying capacity of the slab specimens. Parametric studies were carried out for slabs with thicknesses up to 120 mm. The experimental results confirmed the reliability and accuracy of the FE modelling. The numerical model was further validated by the uniaxial tensile and compressive data and it was found that the model accurately reproduced the material properties behaviour. The thesis also includes an investigation of size effect on the structural strength of UHPFRC elements. This concerns the static flexural behaviour of similar notched UHPFRC beams with various depths under a three-point bending test and the prediction of load-crack mouth opening displacement (CMOD) behaviour. Nonlinear finite element simulations using the CDP model were also conducted and it was found the model can predict full load-CMOD curves, peak-load and crack propagation processes with good agreement with experimental data. Furthermore, a parametric study considering larger sizes of specimens up to a depth of 300 mm was carried out and it was found that the size effect on the beam’s nominal strength is negligible due to the relatively high ductility of UHPFRC compared to other types of concrete.
Supervisor: Schleyer, G. ; Jones, S. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral