No / A discrete particle model is described which simulates bedload transport over a flat bed of a unimodal mixed-sized distribution of particles. Simple physical rules are applied to large numbers of discrete sediment grains moving within a unidirectional flow. The modelling assumptions and main algorithms of the bedload transport model are presented and discussed. Sediment particles are represented by smooth spheres, which move under the drag forces of a simulated fluid flow. Bedload mass-transport rates calculated by the model exhibit a low sensitivity to chosen model parameters. Comparisons of the calculated mass-transport rates with well-established empirical relationships are good, strongly suggesting that the discrete particle model has captured the essential elements of the system physics. This performance provides strong justification for future interrogation of the model to investigate details of the small-scale constituent processes which have hitherto been outside the reach of previous experimental and modelling investigations.

This thesis presents the results of an effort to quantify the implications of using ultra-high performance concrete (UHPC) for shear walls in tall buildings considering structural efficiency and environmental sustainability. The Lattice Discrete Particle Model (LDPM) was used to simulate the response to failure of concrete shear walls without web steel bar reinforcement under lateral loading and constant axial compressive loading. The structural efficiency of UHPC with simulated compressive strength of f'c = 231 MPa was compared to that of a high-performance concrete (HPC) with f'c = 51.7 MPa simulated compressive strength. UHPC shear walls were found to have equal uncracked stiffness and superior post-cracking capacity at a thickness 58% of the HPC shear wall thickness, and at 59% of the HPC shear wall weight. Next, the environmental sustainability of UHPC with compressive strength f'c = 220-240 MPa was compared to that of an HPC with compressive strength f'c = 49 MPa with a life-cycle assessment (LCA) approach, using SimaPro sustainability software. At a thickness 58% of the HPC shear wall thickness, UHPC shear walls with 0% fiber by volume were found to have an environmental impact 6% to 10% worse than that of HPC shear walls, and UHPC shear walls with 2% fiber by volume were found to have an environmental impact 47% to 58% worse than that of HPC shear walls. The results detailed herein will allow for design guidelines to be developed which take advantage of UHPC response in shear. Additionally, this work may be implemented into topology optimization frameworks that incorporate the potential improvements in structural efficiency and sustainability through using UHPC. / Master of Science

This research develops and validates computational tools for the design and analysis of structural components and systems constructed with Ultra-High Performance Concrete (UHPC). The modeling strategy utilizes the Lattice Discrete Particle Model (LDPM) to represent UHPC material and structural member response, and extends a structural-level triaxial continuum constitutive law to account for the addition of discrete fibers. The approach is robust, general, and could be utilized by other researchers to expand the computational capability and simulate the behavior of different composite materials. The work described herein identifies the model material parameters by conducting a complete material characterization for UHPC, with and without fiber reinforcement, describing its behavior in unconfined compression, uniaxial tension, and fracture toughness. It characterizes the effect of fiber orientations, fiber-matrix interaction, and resolves the issue of multi-axial stress states on fiber pullout. The capabilities of the computational models are demonstrated by comparing the material test data that were not used in the parameter identification phase to numerical simulations to validate the models' predictive capabilities. These models offer a mechanics-based shortcut to UHPC analysis that can strategically support ongoing development of material and structural design codes and standards. / Ph. D. / This research develops and validates new computer-based methods to analyze and design civil infrastructure constructed with ultra-high performance concrete (UHPC), achieved when steel fibers are combined with a finely graded cement matrix. With superior performance characteristics in comparison to regular concrete, UHPC is studied herein for its strong potential to advance the durability, efficiency, and resiliency of new and existing infrastructure. The simulation-based methods are extensively verified with novel experiments that evaluate the material limits and failure modes when compressed, bent, or stretched, considering fiber volume and orientation. The computer-based tools can be used to realistically assess the structural performance of innovative UHPC applications in buildings, bridges, and tunnels under natural hazards, leading to surpassed levels of structural efficiency and resiliency across civil infrastructure.

Future sea level rise associated to global warming is one of the greatest societal and environmental challenges of tomorrow. A large part of the contribution comes from glaciers and ice sheets discharging ice and meltwater into the ocean and the recent worldwide increase is worrying. Future predictions of sea level rise try to encompass the complex processes of ice dynamics through glacier modelling but there are still large uncertainties due to the lack of observations or too coarse parameterisation, particularly for processes occurring at the glacier interfaces with the bed (sliding) and with the ocean (calving). This thesis focuses on modelling these processes from two marine-terminating glaciers in Svalbard, Kronebreen and Tunabreen. By inverting three years of high temporal resolution time-series of surface velocities on Kronebreen, basal properties are retrieved with the ice flow model Elmer/Ice in Paper I. Results suggest that surface melt during the summer greatly influences the dynamics of the following season and that sliding laws for such glaciers should be adapted to local and global processes changing in space and time. The subglacial drainage system, fed by the surface melt, is modelled in Paper II during two melting seasons. Results show different configurations of efficient and inefficient drainage systems between years and the importance of using a sliding law dependent on spatio-temporal changes in effective pressure. The interaction with the ocean is incorporated in Paper III by combining a series of models, including an ice flow model, a plume model and a particle model for discrete calving and compares the output with observations. Results show the importance of glacier geometry, sliding and undercutting on calving rate and location. However, more observations and analytic methods are needed. Time-lapse imagery placed in front of Tunabreen have been deployed and a method of automatic detection for iceberg calving is presented in Paper IV. Results show the influence of the rising plume in calving and the front destabilisation of the local neighbourhood.