The introduction of high strength concrete in construction demanded an assessment of the current methods of structural design. In the case of the slabs, the benefits brought about by concretes of higher strength could translate into design of slender sections. Theoretically these sections could be prone to excessive deflections. The flexural behaviour of such structural elements should be carefully assessed. The present thesis addresses a series of particular issues such as deflection at service loads, crack formation and development of tension stiffening and ductility. An experimental program on large-scale samples was conducted. Six one way and four two way slabs made of reinforced high strength concrete were tested under simulated and accurately measured equally distributed loads. Different loading stages were recorded. Crack formation, crack patterns and yield line disposition were observed. The main characteristics of concrete that influence the deflection behaviour were assessed based on collected data and on available literature results. Statistical methods were employed in order to refine empirical equations that help in the design of slabs. To improve the calculation of deflection of slabs a new equation for the effective moment of inertia was proposed. The new formula was integrated into a method of calculating deflection and verified against experimental results. Limits of the use of high strength concrete in slabs were investigated by means of a parametric study. This was designed to answer some questions as: which would be the most important characteristics of high-strength concrete that influence the design and up to what value of strength would the beneficial effect on deflection exhaust its effectiveness. Models based on the refined empirical equations for different concrete parameters were proposed. Another area that has been studied was the ductility of high strength concrete slabs. An analytical comparative study of the ductility of slabs reinforced with steel of different ductility class was conducted. Results were critically appraised and discussed.

An analytical method for determining the crack spacing and crack width in reinforced concrete beams and one-way slabs is presented in this thesis. The locations and the distribution of cracks developed in a loaded member are predicted using the calculated concrete stress distributions near flexural cracks. To determine the stresses, a concrete block bounded by top and bottom faces and two transverse sections of the beam is isolated and analysed by the finite element method. Two types of blocks are analysed. They are: (i) block adjacent to the first flexural crack, and (ii) block in between successive cracks. The calculated concrete stress distribution adjacent to the first flexural crack is used to predict the locations of primary cracks (cracks formed at sections where the stresses have not been influenced by nearby cracks). The concrete stress distributions in between successive cracks, calculated for various crack spacings and load levels, are used to predict the formation of secondary cracks in between existing cracks. The maximum, minimum and the average crack spacing at a given load level are determined using the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width at reinforcement level is determined as the relative difference in elastic extensions of steel and surrounding concrete. The accuracy of the present method is verified by comparing the predicted spacing and width of cracks with those measured by others. The analytical method presented in this thesis is subsequently used to investigate the effects of various variables on the spacing and width of cracks, and the results are presented. These results are used to select the set of parameters that has the most significant effect. A parametric study is then carried out by re-calculating the spacing and width of cracks for the selected parameters. Based on the results of this parametric study, new formulas are developed for the prediction of spacing and width of cracks. The accuracy of these formulas is ascertained by comparing the predicted values and those measured by other investigators on various types of beams under different load levels. The calculated stress distributions between successive cracks are also used to develop a new method of incorporating the tension stiffening effect in deflection calculation. First, curvature values at sections between adjacent cracks are determined under different load levels, using the concrete and steel stresses. These results are used to develop an empirical formula to determine the curvature at any section between adjacent cracks. To verify the accuracy of the new method, short-term deflections are calculated using the curvature values evaluated by the proposed formula for a number of beams, and the results are compared with those measured by others.

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Use of composite steel construction with precast hollow core slabs is now popular in the UK,but the present knowledge in shear capacity of the headed shear studs for this type of composite construction is very limited. Currently, all the information is based on the results obtained from experimental push-off tests. A finite element model to simulate the behaviour of headed stud shear connection in composite beam with precast hollow core slabs is described. The model is based on finite element method and takes into account the linear and non-linear behaviour of all the materials. The model has been validated against the test results, for which the accuracy of the model used is demonstrated. Parametric studies showing the effect of the change in transverse gap size, transverse reinforcement diameter and in-situ concrete strength on the shear connection capacity are presented.

An innovative strengthening technique is applied for the first time in this study to provide flexural strengthening in two-way reinforced concrete (RC) slabs supported on edge beams. The technique comprises external bonding of textiles on the tension face of RC slabs through the use of polymer-modified cement- based mortars. The textiles used in the experimental campaign comprised fabric meshes made of long stitch-bonded fibre rovings in two orthogonal directions. The specimens measured 2 x 2 m in plan and were supported on hinges at the corners. Three RC slabs strengthened by textile reinforced mortar (TRM) overlays and one control specimen were tested to failure. One specimen received one layer of carbon fibre textile, another one received two, whereas the third specimen was strengthened with three layers of glass fibre textile having the same axial rigidity (in both directions) with the single-layered carbon fibre textile. All specimens failed due to flexural punching. The load-carrying capacity of the strengthened slabs was increased by 26%, 53%, and 20% over that of the control specimen for slabs with one (carbon), two (carbon) and three (glass) textile layers, respectively. The strengthened slabs showed an increase in stiffness and energy absorption. The experimental results are compared with theoretical predictions based on existing models specifically developed for two-way slabs and the performance of the latter is evaluated. Based on the findings of this work the authors conclude that TRM overlays comprise a very promising solution for the strengthening of two-way RC slabs.

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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.

Thesis (M.E.-Res.)--University of Wollongong, 2008. / Typescript. Includes bibliographical references: leaf 163-172.

Thesis (M. App. Sc.)--Carleton University, 2002. / Includes bibliographical references (p. 268-281). Also available in electronic format on the Internet.