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The phenomenon of vibration-induced shear resistance reduction (ViSRR) in granular soil is characterized by the loss of shear resistance without significant excess pore pressure generation. It has diverse potential applications in various industries such as mining, pharmaceuticals, and civil engineering, including the installation of vibratory-driven piles. Despite limited research on this topic, both experimentally and theoretically, the mechanism associated with ViSRR remains challenging to explain. There is currently no established constitutive model to properly describe it. This dissertation investigates the fundamental features of ViSRR and develops a model to describe the process that leads ViSRR. To achieve these objectives, three main areas of investigation were undertaken. First, a series of laboratory tests were conducted using a modified triaxial apparatus that allowed for vibrations superimposed on the monotonic shearing of granular soil samples. Second, by correlating macroscopic plastic strains with the transition, creation, and destruction of mesoscopic shear-transformation-zones (STZs), which can be considered as weak particle loops in granular assemblies, the conventional thermodynamic-based STZ model was extended to soil mechanics. Third, the concept of "vibration-induced shear resistance relaxation" was proposed, which refers to the loss of shear resistance in granular material subjected to restricted deformations in response to plastic strains induced by vibrations. In other words, ViSRR occurs when the total deformation rate of the granular material is constrained and does not keep up with the rate of plastic deformation induced by vibrations. By conducting laboratory tests, developing the extended STZ model, and proposing the concept of "vibration-induced shear resistance relaxation", this dissertation contributes to a better understanding of ViSRR in granular soil and provides insights into the mechanisms governing this phenomenon. The results of this research can be used to improve the design and construction of geotechnical structures. / Thesis / Doctor of Philosophy (PhD)

Cross-Laminated Timber (CLT) combines layers of dimension lumber in alternating grain direction to form a mass timber panel that can be used to create entire wall, floor and roof elements. The viability of CLT as an element to resist lateral forces from racking has been of great interest (Dujic et al. 2004, Blass and Fellmoser 2004, and Moosbrugger et al. 2006). However, most research to date has been conducted on full-scale wall panels connected with proprietary fasteners according to European Test Methods. Little research has focused on non-proprietary connections, including nails, bolts and lag screws. The behavior of CLT full-scale wall panels is dependent upon the individual connection properties including the panel-panel connections between adjoining CLT panels within the wall. The purpose of this research is to evaluate the behavior of three small-scale CLT connection configurations using non-proprietary fasteners. Three different connections -LVL surface spline with lag screws, half-lap joint with lag screws, and butt joint with a steel plate fastened with nails - were tested in both monotonic and cyclic tests. In all, 30 connection tests were conducted, with 15 monotonic test and 15 cyclic tests. Connection strength, stiffness, and ductility were recorded for each connection. Experimental values were compared to National Design Specification for Wood Construction, or NDS (AWC 2012) predictions for connection strength. Nailed steel plate connections yielded much greater loads and behaved in a more ductile manner than did the lag screwed connections. The surface spline and half-lap connections often failed in a catastrophic manner usually due to splitting of the spline and fastener failure. Experimental results were generally lower than predicted by the yield models for the surface spline and steel plate connections. The half-lap connection resulted in higher experimental results than predicted. A discussion of the connection strength for materials with a non-homogeneous grain direction is also included. / Master of Science

Experiments were performed to examine the shear resistance of heavily reinforced I-beams. Six I-beams with identical cross sections were constructed using high strength self-consolidating concrete, and were tested under monotonic anti-symmetric loading. All specimens had almost the same amount of longitudinal reinforcement, which provided sufficient flexural capacities. There were two variables: shear span and shear reinforcement ratio. Test results showed that ACI code was too conservative in predicting the shear strengths of heavily shear reinforced I-beams, and the shear strength limit for deep beams should be increased to account for the benefit of high strength concrete. However, doubling the amount of stirrups did not improve the ultimate shear resistance much. The three beams that contained around 2.45% stirrups showed over-reinforced shear failures. Longitudinal flange cracking occurred to every specimen due to lack of cross tie reinforcement in the flanges, and it was believed to have reduced the ultimate shear strength.

Experiments were performed to examine the shear resistance of heavily reinforced I-beams. Six I-beams with identical cross sections were constructed using high strength self-consolidating concrete, and were tested under monotonic anti-symmetric loading. All specimens had almost the same amount of longitudinal reinforcement, which provided sufficient flexural capacities. There were two variables: shear span and shear reinforcement ratio. Test results showed that ACI code was too conservative in predicting the shear strengths of heavily shear reinforced I-beams, and the shear strength limit for deep beams should be increased to account for the benefit of high strength concrete. However, doubling the amount of stirrups did not improve the ultimate shear resistance much. The three beams that contained around 2.45% stirrups showed over-reinforced shear failures. Longitudinal flange cracking occurred to every specimen due to lack of cross tie reinforcement in the flanges, and it was believed to have reduced the ultimate shear strength.

The behaviour of concrete structures subjected to high impulsive loading such as blast involves complex responses at the constituent material as well as local to global structural levels. To fully describe the processes involved, detailed numerical simulation is generally required and it is in fact commonly employed nowadays in this field of investigations. However, the demands on a rigorous computational model with the capability to represent different regimes of responses throughout the entire process, namely the stress wave stage under the immediate impulsive (blast) loading, the development of local composite mechanism (such as shear), and finally the global bending / residual structural state, have not been established nor thoroughly investigated in the literature. This thesis aims to fill in this gap and develop an effective and efficient modelling framework for reinforced concrete (RC) structures under impulsive loading, with a particular focus on the analysis of complex dynamic shear mechanisms and the residual structural capacities. This thesis uses a benchmark RC slab as a testbed to firstly examine the validity of commonly applied finite element setup and typical material models for the analysis of the structural response into the global deformation phase and the residual state. This is followed by a detailed scrutiny of the demands on the concrete material model in terms of preserving a realistic representation of the tension/shear behaviour and the significance of such features in simulating realistically the structural response in a reinforced concrete environment. Deficiencies of a widely used concrete material model, namely the Karagozian and Case concrete (KCC) model, in this respect are investigated and a modification scheme to the relevant aspects of the material model is proposed. The modification is demonstrated to result in satisfactory improvement in terms of ensuring more robust simulation of reinforced concrete response to blast loading. To deal with the inevitable modelling uncertainties in the part of concrete surrounding reinforcing bars in a numerical model, an equivalent transitional layer model is proposed for use in finite element modelling of RC structures subjected to impulsive loading. The main objectives of the equivalent transitional layer are to achieve a consist transfer of stress between rebar to concrete outside the transitional zone, and to maintain a realistic relative “sliding” displacement between the outer edge of the transitional layer and the rebar, while the inner edge of the transitional layer is perfectly bonded (with node-sharing) to the rebar. With appropriate descriptions of the softening and failure of the material for the transitional layer, the deformation profile and the strength can be reasonably represented in a consistent manner using the perfect-bond scheme which is commonly adopted in this field of applications. The transitional layer also incorporates features to ensure mesh-independent bond strength. Validation of proposed transitional layer model is carried out against results from RC pullout and beam experiments. The above modelling framework is subsequently employed to investigate the dynamic shear resistance of RC beam/slab under impulsive loading, recognising that the information on the dynamic shear strength in very scarce in the literature. The influence of loading rate on the change of shear span, which alters the shear resistance mechanism and generally results in an increase of the shear capacity, is discussed. The influence of the strain rate enhancement of the material strength on the dynamic shear capacity is also evaluated.

The purpose of this study was to determine the effect on side shear resistance in limestone when temporary casing is used. Due to testing in actual limestone being an unrealistic goal, simulated limestone mixes were prepared and cast into 6 – 42 in. diameter beds. Limestone throughout Florida can be quite varied (e.g. 50-5000 psi) but where stronger limestone is not likely to be penetrated by casing installation. Therefore, target unconfined compressive strengths of the study specimens ranged between 60 psi to 850 psi. A simulated limestone material was developed based on over 200 cylinders cast for unconfined compression testing where the binder (cement or lime), water to binder ratio, aggregate types (sand, coquina, and oyster shells), and binder content were all varied. Results of the laboratory tests were used to establish simulated limestone mixes for 42 in. diameter specimen beds in which 1/10th scale drilled shaft rock sockets were cast. Drilled shaft casing installation techniques were adapted to 1/10th scale where driven casing and oscillated/rotated casing methods were simulated. Within each of the simulated limestone test beds, 5 shaft specimens were cast with and without temporary casing where at least one of the specimens was cast without temporary casing (control specimen). Pullout tests of each specimen revealed that the presence of temporary casing reduced the side shear by 25 to 28 percent depending on the casing installation/extraction method. However, in all cases representative of weaker limestone, the measured reduction did not affect the anticipated design side shear resistance.

Shear strength of precast/prestressed hollow-core (PHC) slabs subjected to concentrated or line loads, especially near supports, may be critical and usually is the governing criteria in the design. This study presents the second phase of a research program, undergoing at the University of Manitoba, to calibrate the shear equations in the Canadian code for predicting the shear capacity of PHC slabs. This phase includes both experimental and numerical investigations using a finite element analysis (FEA) software package. The length of bearing, void shape and size, level of prestressing and shear span-to-depth ratio were investigated. The experimental results were compared to the predictions of the Canadian, American and European codes. It was concluded that the Canadian code is unduly conservative. However, the special European code for PHC slabs resulted in better and more consistent predictions. The FEA suggested that the adequate prestressing reinforcement ratio to obtain highest shear capacity ranges between 0.7% and 1.1%.

Shear strength of precast/prestressed hollow-core (PHC) slabs subjected to concentrated or line loads, especially near supports, may be critical and usually is the governing criteria in the design. This study presents the second phase of a research program, undergoing at the University of Manitoba, to calibrate the shear equations in the Canadian code for predicting the shear capacity of PHC slabs. This phase includes both experimental and numerical investigations using a finite element analysis (FEA) software package. The length of bearing, void shape and size, level of prestressing and shear span-to-depth ratio were investigated. The experimental results were compared to the predictions of the Canadian, American and European codes. It was concluded that the Canadian code is unduly conservative. However, the special European code for PHC slabs resulted in better and more consistent predictions. The FEA suggested that the adequate prestressing reinforcement ratio to obtain highest shear capacity ranges between 0.7% and 1.1%.