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|Title: ||Load transfer across cracks and joints in concrete slabs on grade|
|Authors: ||Arnold, Stuart J.|
|Keywords: ||Concrete slabs on grade|
Finite element modelling
|Issue Date: ||2004|
|Publisher: ||© Stuart John Arnold|
|Abstract: ||This research has investigated the behaviour of joints and cracks under single and multiple cycles of load. This provides an increased understanding of concrete slab on grade performance, enabling more effective design and monitoring procedures. Examination of the geometry of cracks and joints within concrete slabs on grade has demonstrated that the commonly assumed parallel formation is erroneous. Measurements using embedded strain gauges, coring and surface profile levelling have uncovered that a high percentage of joints will contain larger crack widths at the surface than at the base,
caused by differential shrinkage. The opening itself is relatively linear; however, the top
50mm of the slab is prone to a higher gradient of movement due to the increased drying
effect towards the surface.
A series of deflection tests using a Falling Weight Deflectometer and Prima dynamic
plate enabled slab response under load to be evaluated. Four sites were examined in total
and correlations found between: load transfer, load step, edge cantilever and crack
geometry. This produced valuable information regarding the influence of load transfer
and crack width on the overall slab behaviour. Foundation voiding and crack face free slip
was also shown to influence deflection magnitude.
A small-scale test facility was developed for the assessment of deterioration in various 'V' shaped and parallel crack widths under high cycle loading. The data demonstrated that joint/crack failure contains four distinct phases of deterioration, each of which is controlled by a different mechanism. 'V' shaped cracks produced a much greater load transfer than that of a parallel crack with the incorporation of A142 mesh and steel fibres reducing differential displacement. Load magnitude and aggregate size were also shown to have significant effects. The value of reinforcement was found to assist with
serviceability requirements, keeping displacement within acceptable levels and preventing
the onset of serious degradation
A finite element model was developed to enable the load transfer mechanism results from
the laboratory test to be used in the assessment of full slab response. Simulations of field testing produced a series of lower bounds in respect to deflections and the associated
response calculations. Theoretical behaviour of a typical slab was assessed with subbase support, joint stiffness, slab thickness and the incorporation of a subbase, found to be
highly influential in reducing slab deflections.
The three main sections of work comprising site data collection, laboratory testing and Finite Element modelling have been used together to provide a much greater understanding of the influence of cracks and joints. This has included the deterioration of cracks over time and an examination of how this and other site-based factors affect overall slab behaviour.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Civil and Building Engineering)|
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