Almost from the beginning of the use of reinforced concrete as a structural material, attempts were made to improve the quality and strength of the material by applying prestressing forces. In a patent applied for in 1886 entitled "Constructions of Artificial Stone and Concrete Pavements", P. H. Jackson of San Francisco described several methods of applying prestress forces by stretching ties by turnbuckles, screws and nuts and wedges. Later in 1888 C. F. W. Doehring in Germany, and in 1896 J. Mandl in Austria secured patents for applications of steel and concrete that may quite properly be described as prestressed concrete.

Fifteen plate load tests were performed on dry silt (at three different ranges of porosity) using various sizes of model footings. The purpose of these tests was to investigate the compressibility under foundations. After outlining a section of the theory of elasticity, with certain modifications, attempts were made to correlate the experimental results with this theory and to compare them also with previous work carried out in this chapter of soil mechanics. In concluding, recommendations were given as a guide for future research.

Settlement characteristics of silt have been studied in relation to those of sand and clay. This involved investigation of the immediate elastic settlement due to deformation occurring under constant volume, and consolidation as a function of pore pressure dissipation. Oedometer and Triaxial compression tests (undrained and consolidated-undrained) with pore pressure measurements were performed to obtain the values of the parameters my, the modulus of volume change, E, the elastic modulus, and pore pressure coefficient ’A’.

Historical data of sea ice concentration in Canadian waters are analysed using projections methods (Principal Component Analysis, Singular Value Decomposition, Canonical Correlation Analysis and Projection on Latent Structures) to identify the main patterns of evolution in the sea ice cover. Three different areas of interest are studied: (1) the Gulf of St Lawrence, (2) the Beaufort Sea and (3) the Labrador Sea down to the east coast of Newfoundland. Forcing parameters that drive the evolution of the sea ice cover such as surface air temperature and wind field are also analysed in order to explain some of the variability observed in the sea ice field. Only qualitative correlations have been identified, essentially because of the singular nature of the sea ice concentration itself and the accuracy of available data. However, several statistical models based on identified patterns have been developed showing forecasting skills far better than those of the persistence assumption, which currently remains one of the best 'model' available. Forecasts are tested over periods of time ranging from a few days to several weeks. Some of these models constitute innovative approaches in the context of statistical sea ice forecasting. Some others models have been developed using a probabilistic approach. These models provide forecasts in terms of sea ice severity (low-medium-high), which is often accurate enough for navigation purposes for the three areas of interest. Forecasting skills of these models are also better than the persistence assumption. Finally, an existing dynamic sea-ice model has been adapted and used to predict sea ice conditions in the Gulf of St Lawrence during the Winter season 1992-1993. Simulations provided by this model are compared to the forecasts of different statistical models over the same period of time.

This research program presents an experimental study on the mechanical and thermal properties of different types of concretes at very early ages, (i.e., during hydration). These properties are investigated for temperature-matched curing, sealed curing and air-dried curing. Three types of concretes are studied including normal-strength (30 MPa), medium-strength (70 MPa) and high-strength (100 MPa) concretes. About 300 cylinders and 175 flexural beams were tested to determine the early-age mechanical properties including compressive stress-strain responses, gain of compressive strength, change in elastic modulus and variation of tensile strength. Creep frames and measuring devices were built to enable the experimental determination of early-age creep, with unloaded, companion specimens giving the corresponding shrinkage strains. A temperature-matched curing bath was developed to measure the heat of hydration and to subject 15 cylinders and 12 flexural beams to temperature-matched curing. The thermal properties investigated included the heat of hydration, the thermal conductivity, the specific heat and the coefficient of thermal expansion. Expressions are proposed to predict the development of compressive strength, elastic modulus and modulus of rupture as a function of the type of concrete and the type of curing. / Sub-routines were developed for a finite element thermal analysis program "DETECT" to predict the variation of temperatures during hydration. Additional sub-routines, using the maturity concept, predicted the compressive strength, elastic modulus and tensile strength of each element, in the time domain. An experimental study was performed to observe the effect of different curing conditions and early-form stripping on the temperature and strain development in structural concrete members. Comparisons are made between the measured and predicted temperatures in large concrete columns and precast tee beams and slabs. / Sub-routines were developed to enable incremental stress analysis in the time domain to account for the rapidly changing material properties and the influence of creep. Predictions of the risk of cracking were made and compared with observations from experiments on concrete elements during hydration. Parametric analyses were carried out to determine the influence of key thermal properties, time of formwork removal, creep, and concrete strength on the thermal gradients developed and the risk of thermal cracking.

A two-length-scale turbulence model is introduced in this thesis for the computation of quasi-two-dimensional turbulent shear flow with two distinct length scales of motion. In the model, the turbulence motions of the two distinct length scales are computed separately. The small-scale turbulence is treated as a background component locally in equilibrium while the large-scale turbulence is simulated using a second-order closure procedure. The development of the turbulent shear flows depends on the rate of energy transfer from the large-scale to the small-scale turbulence. Two mechanisms are identified to have a significant effect on the rate of this energy transfer. On one hand, the rate is reduced due to the confinement of the large-scale turbulence to two-dimensional motion, since the nonlinear energy cascade process is less efficient in two-dimensional turbulent motion. On the other hand, the rate is enhanced due to the work done by the large-scale turbulent motion against the friction forces. The energy transfer rate due to friction is derived in the model using a two-step averaging procedure, whereas the transfer rate due to nonlinear cascade process is determined using a model equation. The data from a number of experimental investigations of quasi-two-dimensional turbulent shear flows are analyzed. These data support the notion of the two-length-scale turbulence model, that (i) the maintenance of the turbulent motion depends on the transfer of energy from the large-scale turbulence to the small-scale turbulence, and (ii) the transfer rate is subjected to confinement and friction influences as specified in the model. Numerical computations are conducted using the two-length-scale model and a single-length-scale model. The results are compared with the experimental data. The two-length-scale model is superior in performance compared with the single-length-scale model, particularly in the intermediate region of the flow where both length scales of the turbule

Thin webbed girders have been recognized for a long time as an economical section for taking flexural stress and therefore, are widely used today, not only for stationary structures, but in aircraft and automobile industries as well. However, some restrictions are placed upon the selection of the depth to web thickness (h/t) ratio, in addition to economies.

In view of the apparent conflict of the results obtained by Messrs. R. J. Lindsay and V.A. Vanoni, and especially taking into consideration the probable errors which are relatively large when compared to the variations in turbidity determined, it was concluded that future investigations should be carried out in such a manner as to reduce the probable errors to a minimum. Since the research of R. J. Lindsay was directly concerned with water intakes, and since his conclusions were based on a great many more observations than those of Mr. Vanoni, it may be assumed that his conclusions are more likely to be correct for this specific case, and an attempt should be made to verify them.

This thesis concerns parallel, platform mechanisms, consisting of two distal links that are connected to each other by a set of open kinematic chains, called legs. Particularly, mechanisms with redundant loops, kinematically quite challenging, are investigated. Existing methods of analysis and their shortcomings are outlined and alternatives which help to overcome them are developed. / Definitions and analyses of platform mechanisms, mobility and degree-of-freedom are reviewed. Kinematic analysis and workspace determination of platform mechanisms are thoroughly investigated. / An algebraic method, based on the functional matrix of mechanisms, as defined by Freudenstein, is applied to determine their degree of freedom (DOF). It is shown with examples that this method unambiguously yields the DOF for mechanisms where other methods fail. / The effects of extra legs, and hence, redundant loops, are discussed. The statics, differential and positional kinematics of these mechanisms are investigated. Kinematic-mapping techniques are used to analyze the constraints applied by individual legs to the platform. Current methods of workspace analysis of platform mechanisms are reviewed. A novel technique, which contains both position and orientation information, is introduced. It is shown that this method successfully treats platform mechanisms, with or without redundant loops. However, it may be computationally expensive for some mechanisms, such as spherical wrist mechanisms. An alternative technique, based on the Euler-Rodrigues parameters of a rotation, is also introduced for spherical mechanisms, of both serial and platform types. / The features of some of the methods introduced here are applied to a novel mechanism introduced elsewhere, namely, the double-tetrahedral mechanism (DTM), which it is a paradigm of closed-loop mechanisms with redundant loops.

In recent years, very detailed images of the brain, produced by modern sensor technologies, have given the neuroscientist the opportunity to study the functional activation of the brain under different conditions. The main statistical problem is to locate the isolated regions of the brain where activation has occurred (the signal), and separate them from the rest of the brain where no activation can be detected (the noise). To do this the images are often spatially smoothed before analysis by convolution with a filter f (t) to enhance the signal to noise ratio, where t is a location vector in N dimensional space. The motivation for this comes from the Matched Filter Theorem of signal processing, which states that signal added to white noise is best detected by smoothing with a filter whose shape matches that of the signal. The problem is that the scale of the signal is usually unknown. It is natural to consider searching over filter scale as well as location, that is, to use a filter s-N/2ft/s with scale s varying over a predetermined interval [ s1,s2 ]. This adds an extra dimension to the search space, called scale space (see Poline and Mazoyer, 1994). Siegmund and Worsley (1995) establish the relation between searching over scale space with the problem of testing for a signal with unknown location and scale and find the approximate P-value of the maximum of the scale-space filtered image using the expected Euler characteristic of the excursion set. In this thesis we study the extension of the scale space result to rotating filters of the form | S|--1/4f (S --1/2t), where S is now an N x N positive definite symmetric matrix that rotates and scales the axes of the filter.