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1.
Finite element analyses of prestressed fiber-reinforced polymer floating piles subjected to uplift force have been conducted in this paper. First, parameters of the modified BPE model (bond–slip model at the fiber-reinforced polymer–concrete interface) were calibrated using existing pullout testing data on fiber-reinforced polymer rebars embedded in concrete. Nonlinear spring elements were used in numerical modeling to characterize the bond–slip behavior at the fiber-reinforced polymer–concrete interface. A parametric study was performed to assess the influence of rebar diameter, fiber-reinforced polymer material, embedment length, and concrete strength on the mobilized bond stress. Upon the successful modeling of the pullout performance of fiber-reinforced polymer rebars in concrete, numerical models were developed to investigate the dependence of the uplift performance of floating piles on the prestress level, uplift force, fiber-reinforced polymer type, and compressive strength of concrete. 相似文献
2.
Interplay between capillary, gravity and viscous forces in unsaturated porous media gives rise to a range of complex flow phenomena affecting morphology, stability and dynamics of wetting and drainage fronts. Similar average phase contents may result in significantly different fluid distribution and patterns affecting macroscopic transport properties of the unsaturated medium. The formulation of general force balance within simplified pore spaces yields scaling relationships for motion of liquid elements in which gravitational force in excess of capillary pinning force scales linearly with viscous force. Displacement fluid front morphology is described using dimensionless force ratios expressed as Bond and Capillary numbers. The concise representations of a wide range of flow regimes with scaling relations, and predictive capabilities of front morphology based on dimensionless numbers lend support to certain generalizations. Considering available experimental data, we are able to define conditions for onset of unstable and intermittent flows leading to enhanced liquid and gas entrapment. These results provide a basis for delineation of a tentative value of Bo ∼ 0.05 as an upper limit of applicability of the Richards equation (at pore to sample scales) and related continuum-based flow models. 相似文献
3.
4.
This paper presents an improved generalisation of cation distribution determination based on an accurate fit of all crystal-chemical
parameters. Cations are assigned to the tetrahedral and octahedral sites of the structure according to their scattering power
and a set of bond distances optimised for spinel structure. A database of 295 spinels was prepared from the literature and
unpublished data. Selected compositions include the following cations: Mg2+, Al3+, Si4+, Ti4+, V3+, Cr3+, Mn2+, Mn3+, Fe2+, Fe3+, Co2+, Ni2+, Zn2+ and vacancies. Bond distance optimisation reveals a definite lengthening in tetrahedral distance when large amounts of Fe3+ or Ni2+ are present in the octahedral site. This means that these cations modify the octahedral angle and hence the shared octahedral
edge, causing an increase in the tetrahedral distance with respect to the size of the cations entering it. Some applications
to published data are discussed, showing the capacity and limitations of the method for calculating cation distribution, and
for identifying inconsistencies and inaccuracies in experimental data.
Received: 19 February 2001 / Accepted: 1 June 2001 相似文献
5.
相速度和群速度是研究地震波传播规律和描述介质特性的重要参数,是弹性波传播理论中的核心内容,在理论研究和实际应用中有重要作用.本文根据VTI介质的刚度矩阵,利用Bond变换建立了TTI介质刚度矩阵.再利用TTI介质刚度矩阵,结合弹性动力学的本构方程、牛顿运动微分方程和几何方程,得到了三维TTI介质弹性波波动方程和Christoffel方程.通过本征值方法求解Christoffel方程,推导了三维TTI介质弹性波相速度的解析表达式.利用Berryman和Crampin推导各向异性介质群速度公式,根据三维TTI介质的相速度解析式推导了三维TTI介质群速度解析表达式.数值试例表明,随着各向异性介质参数改变,TI介质弹性波相速度变化较为平缓,群速度变化较为剧烈,qP波和SH波速度变化较为平缓,qSV波速度变化较为剧烈. 相似文献
6.
H. Akgün 《Environmental Geology》1997,31(1-2):34-41
Design of plugs for abandonment of boreholes and shafts may be governed by the bond strength between the plug and host rock.
This paper presents the results of push-out tests on cement grout plugs in salt. Two types of expandable cement grouts have
been tested. The average interface shear strengths ranged from 2 to 12 MPa (290 to 1740 psi). Peak shear stresses at failure,
assuming an elastic stress distribution along the interface, were up to eight times higher. Standard deviations commonly reached
20%. Dissolution along the interface was observed, and may have been enhanced by clay inclusions in the salt. This dissolution
appears to have reduced bond strengths. Application of the results to the design of plugs for larger openings (for example,
shafts, drifts, or boreholes) is discussed.
Received: 6 March 1996 · Accepted: 16 July 1996 相似文献
7.
本文应用热渗滤作用理论,对部分产出在花岗岩体外接触带沉积围岩中的热液铀矿床的形成机制作出合理的解释。在分析热渗滤作用特点及部分岩石热渗滤系数并详细对比了天然岩石中五种存在形成H_2O的物理化学性质的基础上,作者认为参与热渗滤作用的主要是存在于矿物颗粒表面和岩石微裂隙中的结合水(薄膜水和分子结合水)。位于热渗滤带的富铀地层中的H_2O及溶解于其中的铀在热渗滤作用下将朝岩体接触带的增温方向迁移。与传统的概念相反,作者指出。成矿溶液是从矿物粒间和岩石微裂隙朝成矿断裂构造方向运移,尔后在物化条件急剧变化的地段沉淀并逐步富集形成具有工业价值的铀矿床。 相似文献
8.
This paper presents a biconcave bond model to investigate the effect of the cementation between grains on the mechanical behavior of rock. The proposed model considers the shape of the bonds among particles that have a biconcave cement form, based on observations of microscopic rock images. The general equations of the proposed model are based on Dvorkin theory. The accuracy and efficiency of the bond model is improved in three ways. After the biconcave bond model is implemented in the discrete element method software Particle Flow Code in 2 Dimensions, a series of numerical uniaxial compression tests were performed to investigate the relationships between the micro‐ to macro‐parameters. The simulations revealed that the biconcave bond model reflects the effect of micro‐parameters, such as the elastic modulus and Poisson's ratio of the cement, on the macroscopic deformation of cemented granular material. Variations in the bond geometry caused extremely diverse macro‐mechanical behaviors. Experimental results concerning rock demonstrate that the biconcave bond model accurately captures the mechanical behavior of intact rock and supports an innovative method for investigating the relationships between the micro‐ and macro‐parameters of cemented granular material. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
9.
Natural loess is a kind of under-consolidated and unsaturated loose granulates (silts) with its microstructure characterized with large voids and inter-particle cementation. This paper presents a distinct element method (DEM) to investigate its macro- and micro-mechanical behaviour (compression and collapse behaviour) under one-dimensional (1D) compression condition. A relationship between bond strength in DEM model and initial water content is used to develop a bond contact model for loess. Then, DEM structural loess samples are prepared by the multi-layer under-compaction method, and cemented with the bond contact model. The effect of water content and void ratio on compression and collapse behaviour of loess is numerically investigated by simulating 1D compression and wetting tests on the DEM material. The DEM results agree qualitatively with available experimental observations in literatures. The wetting-induced deformation is independent of the sequence of wetting and loading under 1D compression condition. The macroscopic yielding and collapse behaviours are associated with bond breakage on microscopic scale. Moreover, bonds break in one of the two failure types in the simulations, i.e. tensile failure and shear failure (compression-shear failure and tension-shear failure), with bonds broken firstly mainly due to tension followed by shear when the samples are compressed, while mainly due to shear when the samples are wetted under a certain pressure. In addition, the contact orientations and deviator fabrics of contacts under 1D compression and wetting were also investigated. 相似文献
10.
G. V. Gibbs K. M. Rosso D. F. Cox M. B. Boisen Jr. 《Physics and Chemistry of Minerals》2003,30(5):317-320
The average strength, s, of the bonded interactions comprising a cation containing oxide anion coordination polyhedron and the value of the electron
density, ρ(r
c
), at the bond-critical points are inversely correlated with bond length. In each case, the observed bond lengths, R, were modeled with power-law expressions defined in terms of s/r and ρ(r
c
)/r, respectively, where r is the Periodic Table row number of the cation involved in the bonded interaction. On the basis of the close connection between
bond strength and the value of the electron density at the bond-critical point, we conclude that bond strength is a direct
measure of bond type; the greater its value, the greater the localization of electron density in the binding region and the
greater the shared–electron covalent character of the bonded interaction.
Received: 15 October 2002 / Accepted: 17 February 2003
Present address:G. V. Gibbs in care of M. Spackman Department of Chemistry, University of New England, Armidale 2351, Australia
Acknowledgements The NSF is thanked for supporting this study with grant EAR–9627458. The paper was written while GVG was a Visiting NSF Scholar
at The University of Arizona. The faculty and graduate students of the Department of Geosciences and Bob Downs and Marelina
Stimpf in particular are thanked for making the visit great fun. 相似文献