1,721,151 research outputs found
Continuum Analytical Models for the Ultimate Limit State Design of Energy Piles
No full textEnergy piles are foundation elements having the double role of transferring structural loads and exchanging heat with the surrounding soil for heating and cooling of buildings. Because of the restraining action exerted by the soil, the temperature variation of piles leads to stresses that combine with those resulting from mechanical loads. The proposed work presents a continuum analytical model for the evaluation of the thermally induced axial force developing as a consequence of the thermal interaction between the pile and the surrounding soil. Solutions are derived for end-bearing piles installed in a homogeneous soil and in a soil deposit with linearly increasing stiffness with depth. The results obtained with the proposed formulae are compared with exact Winkler-based analytical solutions already available in literature as well as with more complex numerical analyses, proving to be a simple and effective tool for the ultimate limit state design of energy piles
A practical method to design thermally stressed piles
No full textThe paper deals with the analysis and design of energy piles subjected to a cyclic temperature variation under constant mechanical axial load. The problem is first investigated through fully coupled thermo-hydro-mechanical analyses using the finite-element code ABAQUS. A single pile, whose head is either free or restrained, is embedded in a normally consolidated clay obeying different constitutive models. Numerical results are reported and discussed with emphasis on the role of the different constitutive assumptions on the development of the pile axial force due to the thermal load. Further, a design procedure is proposed to derive the maximum thermally induced axial load by using recently developed analytical solutions, worked out to obtain explicit formulae that can be readily employed in a spreadsheet for the direct computation of axial force in a multilayer soil. The method consists of employing these expressions after identifying some rules to: (a) select the soil stiffness profile as a function of the mechanical load and (b) establish the effect of the actual restraint condition at the pile head as a function of the stiffness ratio between the inactive and the active pile subgroups. The main advantage of the proposed procedure is that it requires only the load–settlement curve under the mechanical axial load, which is always assessed in pile design, through analytical, numerical or experimental means. After a comparison with the results of the finite-element analyses, the procedure is also applied to a number of field tests on groups of energy piles available in the literature, and provides a satisfactory match between measurements and predictions
A closed-form solution for the failure interaction diagrams of pile groups subjected to inclined eccentric load
No full textThe work at hand proposes a method for assessing, under reasonable hypotheses from an engineering perspective, the failure envelope of a pile group subjected to generalized loading conditions involving a vertical and a lateral force along with a moment. Following different assumptions of increasing complexity, a simple closed-form expression, which is however capable of considering also the strong dependence of sectional yielding moment on the axial force, is derived. The use of such formula, which allows a practical hand calculation of the interaction diagrams at failure, returns conservative yet very accurate results. As a follow up, with reference to reinforced concrete piles, design considerations involving both structural and geotechnical failure under lateral load are reported. It is found that for most cases, if steel reinforcement is established to resist the design bending moment, the geotechnical Ultimate Limit State checks are automatically satisfied
Finite element analyses of energy piles using different constitutive models
No full textEnergy piles are foundation elements having the double scope of transferring structural loads from the structure to the ground and of exchanging heat with the surrounding soil. It follows that pile state of stress and settlement are altered by the time-dependent temperature change in both pile and soil. This work is aimed at investigating the effect of thermal cycles on the behaviour of a single energy pile. To this end, fully coupled thermo-hydro-mechanical analyses have been carried out using the Finite Element code ABAQUS. The single pile is installed in a normally consolidated clay behaving according to different constitutive models involving Mohr-Coulomb, Modified Cam Clay and Hypoplastic. The latter is employed with and without the thermal formulation capable of accounting for the thermal collapse of NC clays during heating. A single free-head pile is considered and the results are presented in terms of pile axial force and settlement developed cycle by cycle
Control of oocyte recruitment: regulative role of follicle cells through the relase of a diffusible factor
No full textTo determine whether oogonial proliferation and oocyte recruitment are under control of hypophyseal and/or ovarian factors, we carried out a series of investigations using Podarcis sicula, a lizard inhabiting the temperate lowlands of Europe in which oocyte recruitment occurs throughout the year, as animal model. Germinal beds containing oogonia and oocytes in prefollicular stages were cocultured with different ovarian compartments in presence/absence of FSH, and the effects of different treatments were evaluated by counting the number of prelepto-leptotene oocytes. Results revealed that oocyte recruitment from the pool of oogonia is under the control of a factor released by follicle cells while FSH has an indirect effect on modulating oogonial proliferation. SDS-PAGE analyses carried out on media conditioned by follicles suggest that the factor involved in the control of oocyte recruitment may be a small protein (about 21 kDa) and that its release is dependent on the period of the ovarian cycle but apparently not on the circulating levels of FSH
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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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