Advanced Theoretical and Computational Methods for Complex Materials and Structures

The broad use of composite materials and shell structural members with complex geometries in technologies related to various branches of engineering has gained increased attention from scientists and engineers for the development of even more refined approaches and investigation of their mechanical behavior. It is well known that composite materials are able to provide higher values of strength stiffness, and thermal properties, together with conferring reduced weight, which can affect the mechanical behavior of beams, plates, and shells, in terms of static response, vibrations, and buckling loads. At the same time, enhanced structures made of composite materials can feature internal length scales and non-local behaviors, with great sensitivity to different staking sequences, ply orientations, agglomeration of nanoparticles, volume fractions of constituents, and porosity levels, among others. In addition to fiber-reinforced composites and laminates, increased attention has been paid in literature to the study of innovative components such as functionally graded materials (FGMs), carbon nanotubes (CNTs), graphene nanoplatelets, and smart constituents. Some examples of smart applications involve large stroke smart actuators, piezoelectric sensors, shape memory alloys, magnetostrictive and electrostrictive materials, as well as auxetic components and angle-tow laminates. These constituents can be included in the lamination schemes of smart structures to control and monitor the vibrational behavior or the static deflection of several composites. The development of advanced theoretical and computational models for composite materials and structures is a subject of active research and this is explored here for different complex systems, including their static, dynamic, and buckling responses; fracture mechanics at different scales; the adhesion, cohesion, and delamination of materials and interfaces

Coupled Field Equations for Saturated Soils and Its Application to Piezocone Penetration and Shield Tunneling.

An elasto-plastic coupled system of equations are formulated here in order to describe the time-dependent deformation of saturated cohesive soils. Formulation of these equations is based on the principle of virtual work and the theory of mixtures for inelastic porous media as proposed by Prevost (1980) and Kiousis and Voyiadjis (1988). The saturated soil is considered as a mixture consisting of two deformable media, the solid grains and the water. Each medium is regarded as a continuum and follows its own motion. The coupled equations are developed for large deformations with finite strains in an updated Lagrangian reference frame. The coupled behavior of the two phase material is implemented into the finite element program GAP/CTM (Geotechnical Analysis Program based on the Coupled Theory of Mixtures), which is developed by the author. This formulation is applied in the analysis of two geotechnical problems. The piezocone penetration and the shield tunneling in cohesive soils. The piezocone penetration in cohesive soils is numerically simulated and implemented into the finite element program (GAP/CTM). The continuous penetration of the cone is simulated by applying an incremental vertical movement of the cone tip boundary. The numerical simulation is done for two cases. In the first case, the interface friction between the soil and the piezocone penetrometer is neglected. In the second case, interface friction is assumed between the soil and the piezocone. Results obtained from the simulation using the proposed model are compared with those obtained from the miniature piezocone penetration tests (PCPT) for cohesive soil specimens conducted at the LSU calibration chamber. The resulting excess pore pressure distribution and its dissipation using the numerical model are compared with some available predicting methods. A two-dimensional computational model is developed in order to simulate the continuous advance of the Earth Pressure Balance (EPB) Shield during the tunneling process in cohesive soils. This model is implemented into the finite element program (GAP/CTM). The computational model is based on the plane strain transverse-longitudinal sections that can incorporate the three-dimensional deformation of the soil around and ahead of the shield face. The continuous shield advance is modeled using the remeshing technique. This model has been used to analyze the N-2 tunnel project constructed in 1981 in San Francisco, California

Advanced Underground Space Technology

The recent development of underground space technology makes underground space a potential and feasible solution to climate change, energy shortages, the growing population, and the demands on urban space. Advances in material science, information technology, and computer science incorporating traditional geotechnical engineering have been extensively applied to sustainable and resilient underground space applications. The aim of this Special Issue, entitled “Advanced Underground Space Technology”, is to gather original fundamental and applied research related to the design, construction, and maintenance of underground space

Finite element study of tunnel-soil-pile interaction

Master'sMASTER OF ENGINEERIN

Semi-analytical predictive model for natural and artificial thawing of circular ground-Ice walls

Artificial ground freezing (AGF) is a ground improvement technique enabling the construction of underground structures in challenging geological conditions. After constructing an underground structure within the ground- ice cofferdam, the soil undergoes a thawing process that can impact the structure stability and waterproofing properties of the lining. Minimizing or preventing potential damage, as well as avoiding delays in construction, can be achieved through a rational design of thawing regimes. In this paper, we present a semi-analytical model for the thermal behaviour of ice-wall during its natural or artificial thawing. The process is described by three independent one-dimensional mathematical problems: the thawing of the outer surface of the ice wall, the thawing of its inner surface, and the thawing of soils around the freeze pipes (in the case of artificial thawing). The proposed approach facilitates the calculation of natural and artificial thawing times and the power required for artificial thawing. The efficiency of the model is demonstrated by comparison with numerical simulation results. This makes the approach suitable and desirable for engineering practice. Importantly, the model allows for seamless analysis of several combinations of influencing factors to select thawing parameters aligned with the requirements of different construction projects

Performance-based damage assessment of masonry structures subjected to settlement using rigid block models

The issue of built Cultural Heritage (CH) exposed to natural hazards is a challenging topic in both research and engineering practice. In the last decades, many efforts were addressed to the protection of CH against seismic hazard, which is the main threat for the integrity and stability of structures. On the other hand, settlements induced by hydrogeological phenomena such as subsidence and landslides also represent a severe risk for existing buildings. Nevertheless, the investigation of damage induced by settlements on structures is a still open challenge. Empirical approaches were proposed, commonly based on the assessment of damage in terms of local parameters, e.g. crack widths. However, the severity of crack width can be affected by different factors such as structural configuration, masonry texture and material properties. Thus, models for the quantitative assessment of damage in terms of global safety levels of structures subjected to foundation movements are demanded. In this framework, this dissertation thesis aims at the development and application of a numerical approach based on rigid block modelling for the performance-based damage assessment of masonry structures subjected to settlement. Two in-house numerical models are proposed, namely a rigid block model with rigid contacts for the linear kinematic analysis and a rigid block model with no-tension elastic contacts for the non-linear kinematic analysis. The first tool aims at the prediction of the failure shape for settled structures as well as the value of the base reaction at the onset of mechanism. It is worth noting that masonry buildings usually exhibit a resilient safety behaviour with respect to settlements. Conversely, appropriate considerations of serviceability limit state are demanded to control damage on the structure and preserve the aesthetics. To this end, the non-linear kinematic model aims to predict the response of masonry structures under settlements also in the early damage states. The output is mainly represented by specific capacity curves, named "push-down curves", where the loss of base reaction is plotted as a function of the displacement of a control point at the settling support. Thus, the numerical formulation allows the damage propagation monitoring, from crack opening until incipient collapse. The dissertation thesis explores the possibility to use such a capacity curve to propose criteria for the displacement-based damage assessment and quantification. A comparison of the proposed approach with empirical damage classification methods is performed

Geotechnical Engineering for the Preservation of Monuments and Historic Sites III

The conservation of monuments and historic sites is one of the most challenging problems facing modern civilization. It involves, in inextricable patterns, factors belonging to different fields (cultural, humanistic, social, technical, economical, administrative) and the requirements of safety and use appear to be (or often are) in conflict with the respect of the integrity of the monuments. The complexity of the topic is such that a shared framework of reference is still lacking among art historians, architects, structural and geotechnical engineers. The complexity of the subject is such that a shared frame of reference is still lacking among art historians, architects, architectural and geotechnical engineers. And while there are exemplary cases of an integral approach to each building element with its static and architectural function, as a material witness to the culture and construction techniques of the original historical period, there are still examples of uncritical reliance on modern technology leading to the substitution from earlier structures to new ones, preserving only the iconic look of the original monument. Geotechnical Engineering for the Preservation of Monuments and Historic Sites III collects the contributions to the eponymous 3rd International ISSMGE TC301 Symposium (Naples, Italy, 22-24 June 2022). The papers cover a wide range of topics, which include: 　 - Principles of conservation, maintenance strategies, case histories - The knowledge: investigations and monitoring - Seismic risk, site effects, soil structure interaction - Effects of urban development and tunnelling on built heritage - Preservation of diffuse heritage: soil instability, subsidence, environmental damages The present volume aims at geotechnical engineers and academics involved in the preservation of monuments and historic sites worldwide

The effect of pipe bursting on nearby utilities, pavement, and structures

This dissertation has involved field and analytical studies of ground movements, ground vibrations and other design issues associated with trenchless pipe replacement (or pipe bursting, as it is commonly known). The process is used to replace an existing underground service pipe with a completely new pipe but without the disturbance and cost of excavating a trench from the surface. The process typically involves the insertion of a tool into the existing pipe that has a maximum diameter that is slightly larger than the existing pipe. This tool is used to break the existing pipe into pieces and to displace the pieces and neighboring soil outwards into the surrounding ground while a new pipe is installed behind the tool. There are several variations of the process with different approaches to various aspects of the breakage and replacement. The trenchless pipe replacement offers advantages of low cost, reduced surface disturbance, and the ability to replace an old pipe with a new pipe of equal or larger diameter and capacity Concerns about the use of the method have centered principally on the ground movements and vibrations produced by the technique--particularly when existing pipe is being replaced by a larger diameter pipe-- and also on any damage experienced by the replacement pipe as it is being pulled into the ground. By further development of the understanding of the effects of the process and by refining the safe limits for the replacement process in terms of soil type, groundwater conditions, type of pipe being burst, degree of up-sizing, proximity to existing services, depth below the street, etc., it is expected that many of the concerns expressed by owners and consultants about the use of the techniques will be allayed and attention directed to the particular circumstances where special precautions need to be used. The cost advantages inherent in on-line replacement over open-cut replacement in many circumstances, and the resulting potential growth of this market, make the improved understanding of ground movements and impacts on adjacent structures well worthwhile

Statistical modelling of nano CMOS transistors with surface potential compact model PSP

The development of a statistical compact model strategy for nano-scale CMOS transistors is presented in this thesis. Statistical variability which arises from the discreteness of charge and granularity of matter plays an important role in scaling of nano CMOS transistors especially in sub 50nm technology nodes. In order to achieve reasonable performance and yield in contemporary CMOS designs, the statistical variability that affects the circuit/system performance and yield must be accurately represented by the industry standard compact models. As a starting point, predictive 3D simulation of an ensemble of 1000 microscopically different 35nm gate length transistors is carried out to characterize the impact of statistical variability on the device characteristics. PSP, an advanced surface potential compact model that is selected as the next generation industry standard compact model, is targeted in this study. There are two challenges in development of a statistical compact model strategy. The first challenge is related to the selection of a small subset of statistical compact model parameters from the large number of compact model parameters. We propose a strategy to select 7 parameters from PSP to capture the impact of statistical variability on current-voltage characteristics. These 7 parameters are used in statistical parameter extraction with an average RMS error of less than 2.5% crossing the whole operation region of the simulated transistors. Moreover, the accuracy of statistical compact model extraction strategy in reproducing the MOSFET electrical figures of merit is studied in detail. The results of the statistical compact model extraction are used for statistical circuit simulation of a CMOS inverter under different input-output conditions and different number of statistical parameters. The second challenge in the development of statistical compact model strategy is associated with statistical generation of parameters preserving the distribution and correlation of the directly extracted parameters. By using advanced statistical methods such as principal component analysis and nonlinear power method, the accuracy of parameter generation is evaluated and compared to directly extracted parameter sets. Finally, an extension of the PSP statistical compact model strategy to different channel width/length devices is presented. The statistical trends of parameters and figures of merit versus channel width/length are characterized

Pile behaviour subject to excavation-induced soil movement in clay

Ph.DDOCTOR OF PHILOSOPH