1,720,962 research outputs found
Thermo-mechanical analysis of energy piles through numerical and centrifuge tests
No full textFor over thirty years, finite element analyses and centrifuge tests have been successfully applied to investigate the response of a large series of geotechnical engineering problems. However, although the capability of finite element analysis to capture the thermal-induced mechanical behaviour of real-scale energy piles has been assessed, the suitability of centrifuge tests for the same purpose has not yet been validated despite their increasing application. This paper investigates the capability and suitability of centrifuge tests for describing the thermal-induced mechanical behaviour of energy piles based on a comparison between a series of results obtained through numerical and centrifuge analyses. In particular, it analyses the response of energy piles in dry sand subjected to mechanical and thermal loads. The study outlines the appropriateness of centrifuge tests for the considered purpose and remarks crucial points that have to be considered when modelling energy pile-related-problem
A non-linear constitutive model for describing the mechanical behaviour of frozen ground and Permafrost
No full textThe mechanical behaviour of frozen ground and permafrost is changing under the increasing variation of
environmental and anthropogenic boundary conditions. This phenomenon affects many civil structures and
infrastructures built in Polar and Alpine areas. Mathematical formulations able to capture the mechanical
behaviour of frozen ground and permafrost with adherence to reality and a limited employment of
technical resources and time appear crucial for the engineering design and retrofit of these structures. To
address this challenge, this study presents a relatively simple elasto-plastic constitutive model for capturing
the non-linear mechanical behaviour of frozen silt. The model is based on associated flow rules.
It employs an elliptical yield surface and a parabolic yield surface for describing the volumetric mechanisms
that characterise the modelled material, together with a parabolic yield surface for describing the
deviatoric mechanism. Comparisons with experimental triaxial test results available in the literature highlight
the suitability of the model to capture the non-linear mechanical response of frozen silt subjected to
both low and high confining pressures. This result, together with the doable implicit consideration in the
model of the effects induced by environmental boundary conditions such as temperature on the mechanical
behaviour of the material, makes this tool attractive for simplified yet thorough analyses of frozen ground
and permafrost-related problems
Thermo-mechanical performance of energy pile groups
No full textEmploying geostructures as structural supports and geomaterials as reservoirs for the extraction and storage of heat represent effective means to meet human activity needs since ancient times. This doctoral thesis focuses on the thermo-mechanical behaviour and performance of an innovative, multifunctional technology that couples the aforementioned roles for the structural support and energy supply of any type of built environment, i.e., energy piles. The multifunctional role of energy piles involves mechanical and thermal loads applied to such geostructures. These loads pose unprecedented challenges to engineers because they cause variations in the temperature, stress, deformation and displacement in the subsurface that need to be considered during analysis and design. Prior to this work, a substantial amount of research had been made available to address the thermo-mechanical performance of single energy piles. Design guidance has also been proposed to advise in the geotechnical and structural design of such geostructures. However, energy pile foundations do not consist of a single energy pile but of a group of energy piles. In this framework, (i) limited knowledge, if available, was present to address the thermo-mechanical behaviour and performance of energy pile groups subjected to thermal and mechanical loads; (ii) no simplified models and methods were accessible to perform the analysis and design of energy pile groups against the action of such loads; and (iii) no comprehensive framework for the effect of thermal (and mechanical) loads on the performance and the related design of both single and groups of energy piles was avail-able. To address such challenges, this doctoral research was performed to (i) investigate the thermo-mechanical behaviour and performance of energy pile groups over typical time-scales of practical applications via the first available in situ tests and coupled numerical analyses of such geostructures; (ii) provide the only simplified analytical models and methods for predicting the vertical deformation of energy pile groups subjected to thermal and mechanical loads; and (iii) propose a comprehensive framework for the effect of thermal and mechanical loads on the performance and related performance-based design (e.g., geotechnical and structural) of single and groups of energy piles. The results presented in this thesis suggest the conclusion that (a) the thermo-mechanical behaviour and performance of energy pile groups are critically different from those of single energy piles; (b) thermal loads, applied alone or in conjunction to mechanical loads, represent a serviceability and not an ultimate limit state problem; and (c) no energy pile analysis and design can be considered complete without addressing the behaviour of piles as both isolated elements and in a group.LM
Performance-based Design of Energy Pile Foundations
No full textOver the past twenty years, an increasing amount of research has been performed to understand the multiphysical behaviour and to address the geotechnical and structural design of so-called energy piles, i.e. deep foundations that can serve any superstructure as both structural supports and geothermal heat exchangers. The coupled application of thermal and mechanical loads to energy piles, due to their multifunctional operation, represents a challenge. Currently, knowledge about the response of energy piles subjected to thermal and mechanical loads is accessible, along with some design guidance. However, this knowledge is fragmented and no recognised performance-based design framework is available. Looking at such challenge, this paper presents a theoretical and experimental analysis of the multiphysical behaviour of energy piles, as well as a performance-based design framework for such foundations. The work highlights that thermal loads involve effects that can be neglected in the design of energy piles at ultimate limit states and can be considered relevant only at serviceability limit states. Based on this result, the performance-based design of energy piles at ultimate limit states reduces to a conventional pile design process while the design at serviceability limit states must account for a number of proposed provisions and verifications.LM
Analysis and Design of Energy Geostructures
No full textAnalysis and Design of Energy Geostructures gathers in a unified framework the theoretical and experimental competence available on energy geostructures: innovative multifunctional earth-contact structures that can provide renewable energy supply and structural support to any built environment. The book covers the broad, interdisciplinary and integrated knowledge required to address the analysis and design of energy geostructures from energy, geotechnical and structural perspectives. This knowledge includes (Part A) an introduction to the technology; (Part B) the fundamentals of heat and mass transfers as well as of the mechanics of geomaterials and structures required to address the unprecedented behavior of energy geostructures; (Part C) the experimental evidence characterizing the considered geostructures; (Part D) various analytical and numerical modeling approaches to capture the response of energy geostructures; and (Part E) the performance-based design and detailing essentials of energy geostructures. Designed with civil engineers in mind, this book targets energy engineers, environmental engineers, geologists, architects and urban project managers as well.LM
Analysis of the vertical displacement of energy pile groups
No full textOver the last fifty years, the interaction factor method has been widely used to address the vertical displacement and the increased deformation of conventional pile groups subjected to mechanical loads when group effects and interactions occur among the piles. Design charts and analytical models have been proposed to serve the considered analysis method. In recent years, the interaction factor method has been extended to address energy pile groups subjected to thermal loads. Design charts have been proposed. However, prior to this study, no analytical models capable of analysing the vertical displacement and the increased deformation of energy piles subjected to thermal loads in a more comprehensive and flexible way than through design charts have been available. To address this challenge, this study presents two analytical performance models for analysing the vertical displacement of energy pile groups subjected to thermal loads, based on the analysis of a single isolated energy pile. Comparisons with three-dimensional finite element analyses outline that the models can accurately capture the displacement of energy piles without the expense of a full rigorous analysis. This evidence makes the present performance models useful tools for the analysis and design of energy piles under serviceability conditions.LM
Equivalent pier analysis of full-scale pile groups subjected to mechanical and thermal loads
No full textThis study presents an equivalent pier analysis of the vertical deformation and displacement of full-scale pile groups subjected to mechanical and thermal loads that are associated with a structural support and a geothermal heat exchanger operation, respectively. Based on the simulation of the behavior of a single representative pile, the investigation addresses pile groups characterized by different end-restraint and site conditions through the equivalent pier method. Loading levels of varying significance, which can be associated to a reversible response of the piles in the group as well as to an irreversible response due to the occurrence of plastic strains in the ground, are considered. Provided that appropriate modeling assumptions are made, the considered formulation of the equivalent pier method can effectively capture the vertical deformation and displacement of pile groups subjected to mechanical and thermal loads. The previous result provides further evidence on the capability of the equivalent pier method to appropriately and effectively serve the analysis and design of pile groups subjected to loading.LM
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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