The friction and deformation behaviour of rock joints

SummaryThe Friction and Deformation Behaviour of Rock Joints The present investigation deals with the influence of joint roughness and material strength on the friction and deformation behaviour of rough indented joints. Besides the analytical determination of the joint roughness by the dilatation behaviour of the joint, friction tests on models with natural joint morphology and rock samples have been conducted.A material law is developed, describing the friction resistance and the dilatation behaviour at large deformations in their dependence on normal stress and material strength.

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ZusammenfassungDas Reibungs- und Verformungsverhalten von Klüften Die vorliegende Untersuchung war dem Einfluß der Kluftflächenunebenheit und der Materialfestigkeit auf das Reibungs- und Verformungsverhalten rauher, verzahnter Kluftflächen gewidmet.Neben der analytischen Bestimmung der Kluftflächenunebenheit anhand des Dilatationsverhaltens der Kluftfuge wurden Reibungsversuche an Modellkörpern mit natürlicher Kluftmorphologie und an Gesteinen durchgeführt. Es wird ein Stoffgesetz entwickelt, mit welchem der Reibungswiderstand und das Dilatationsverhalten in Abhängigkeit von der Normalspannung und der Materialfestigkeit bei längeren Gleitwegen beschrieben werden kann.

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RésuméLe comportement des fissures au frottement et aux déformations La présente étude traite de l'influence de la rugosité d'une diaclase et de la résistance de la roche sur le comportement au frottement et aux déformations d'une fissure âpre et endentée. La rugosité de la fissure a été déterminée d'après la dilatation maximale. Des éssais de frottement ont été exécutés à l'aide de modèles ayant une surface de fissure naturelle et à l'aide d'échantillons de roche. Une loi a été développée qui décrit la resistancé au frottement et le comportement à la dilatation de la fissure pour de grandes déformations en fonction de la contrainte normale et de la résistance des matériaux.

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List of Symbols h dilatation - i deviation angle, dilatation angle - s shear deformation - residual friction angle - normal stress - _F tensile strength - shear stress With 15 Figures     

不同加腋宽度下钢筋混凝土偏心节点的抗裂性能

通过五榀钢筋混凝土梁柱偏心节点试件在低周反复荷载下的试验研究，探讨了不同梁端水平加腋宽度对节点核芯区抗裂性能的影响，提出偏心节点抗裂度计算的建议公式。     

Lithological control on the elevation of shore platforms in a microtidal setting

The shore platforms on Shag Point, southern New Zealand, are quasi‐horizontal surfaces and are developed between supratidal and low water spring levels. A range of morphologies occur, with more exposed platforms having a distinct low‐tide cliff, in contrast to low‐tide surfaces where the seaward edge is buried beneath rubble and macro‐algal growth. The platforms range in width from 20 to 80 m and are eroded into Late Cretaceous/Early Tertiary fine marine sandstones and mudstones. Shore platforms have formed in two principal lithological units: a homogeneous unit that is characterized by few discontinuities, and a fractured unit with joints spaced about 0·5 m apart. Rock hardness is low in both units (L‐type Schmidt hammer rebound values of 31 ± 4), and there is little systematic variation in values between the two units in which platforms have developed. Case‐hardened concretions within the sandstone are significantly harder than surrounding rock and cause local relief of metre scale as the spherical diagenetic features are eroded from the bedrock. They do not, however, appear to affect broad‐scale platform geometry. Joints within the bedrock are a primary control on platform elevation. Platforms formed in jointed rock occur at the lower portion of the intertidal zone, in contrast to platforms formed in unjointed bedrock, in which horizontal surfaces occur at or above mean high water spring tide level. Rock structure, therefore, appears to be the primary determinant factor of platform geometry at Shag Point. Copyright © 2006 John Wiley & Sons, Ltd.     

岩石节理的渗流广义立方定理

首先讨论了岩石节理的渗流立方定理及其适用条件，然后从渗流与变形耦合的角度，论述了节理的开度性质，并提出了适用于一般节理的渗流广义立方定理，最后用有限元数值模拟方法验证了广义立方定理。     

Neotectonics and extension direction of the Southern Kenya Rift, Lake Magadi area

The Magadi area, located in the southern part of the Kenya Rift, is a seismically active region where rifting is still in progress. The recent tectonic activity has been investigated through a seismological survey and the study of neotectonic joints found in Lake Magadi sediments, which were deposited some 5000 years ago. The structural analysis of these open fractures was combined with a quantitative analysis of the orientation and size characteristics of imagery faults. The gathered data demonstrate (1) that the majority of the systematic joints have straight and parallel trajectories with a common en echelon mode of propagation displayed through a rich variety of patterns, and (2) that there is a self-similarity in fault and joint principal directions recognised at the different telescopic scales. SPOT image (1:125,000), aerial photos (1:76,000), and outcrop fieldwork reveal two important structural orientations which are N015°E and N015°W. The N015°E regional direction is consistent with the orientation of the southern segment of the Kenya Rift. Structural analysis is supported by results of a joint microseismic investigation in the Lake Magadi area. Obtained focal mechanism solutions indicate an E–W to ESE–WNW normal faulting extension direction.     

Characterization and reconstruction of a rock fracture surface by geostatistics

It is well understood that, in studying the mechanical and hydromechanical behaviour of rock joints, their morphology must be taken into account. A geostatistical approach has been developed for characterizing the morphology of fracture surfaces at a decimetre scale. This allows the analysis of the spatial variability of elevations, and their first and second derivatives, with the intention of producing a model that gives a numerical three‐dimensional (3D) representation of the lower and upper surfaces of the fracture. Two samples (I and II) located close together were cored across a natural fracture. The experimental data are the elevations recorded along profiles (using recording steps of 0.5 and 0.02 mm, respectively, for the samples I and II). The goal of this study is to model the surface topography of sample I, so getting estimates for elevations at each node of a square grid whose mesh size will be, for mechanical purposes, no larger than the recording step. Since the fracture surface within the sample core is not strictly horizontal, geostatistical methods are applied to residuals of elevations of sample I. Further, since structural information is necessary at very low scale, theoretical models of variograms of elevations, first and second derivatives are fitted using data of both that sample I and sample II. The geostatistical reconstructions are computed using kriging and conditional simulation methods. In order to validate these reconstructions, variograms and distributions of experimental data are compared with variograms and distributions of the fitted data. Copyright © 2002 John Wiley & Sons, Ltd.     

复式钢管混凝土外肋环板节点抗剪承载力研究

在已有理论和试验研究的基础上,对复式钢管混凝土外肋环板节点的抗剪受力性能进行分析。建立了节点核心区的抗剪受力模型,将节点域抗剪贡献分为三部分:节点域内外钢管腹板的抗剪贡献、节点主要连接件竖向肋板与锚固腹板的抗剪贡献以及节点域混凝土的抗剪贡献,推导了复式钢管混凝土柱节点屈服抗剪承载力和极限抗剪承载力的计算公式,为复式钢管混凝土柱节点的工程设计提供承载力计算方法。理论得到的节点屈服剪力和极限剪力值与试验结果进行了对比,并提出抗剪能力储备系数这一新指标反映节点的抗剪切破坏能力,量化地解释了节点发生梁铰破坏后抗剪能力的安全储备。得出此类新型节点在破坏时抗剪储备能力充足,可保证节点达到良好延性的破坏模式,说明节点设计符合强剪弱弯的抗震设计原则。     

Damage sequence and safety margin assessment of expansion joints by shake table testing

The performance of nonstructural components has attracted attention, and previous large earthquakes have resulted in widespread damage to expansion joints. In contrast to the main structural components, for which ductility beyond the design tolerance is ensured, the safety margin of nonstructural components classified as the product of mechanical engineering, such as expansion joints, is uncertain. This paper investigates the damage sequence and safety margin of expansion joints through shake table testing. The expansion joints were installed to connect 2 rigid steel frames with short and long natural periods. Four commonly used types, high-performance and standard-performance floor and wall expansion joints, were tested. Seven damage patterns of the 4 expansion joints were observed, and most of the damage patterns were considered displacement dependent. The damage mechanisms and relative displacements at the moment of damage were identified by using strain gauges attached near collision and damage locations. The high-performance expansion joints showed only minor damage beyond the design motion range, whereas the standard-performance expansion joints exhibited minor damage below the design motion range and failure at the design motion range or slightly beyond. For each damage state, repair information was obtained through a questionnaire to an expansion joint manufacturer, and the sum of the initial cost and repair cost for high-performance and standard-performance expansion joints was compared. The results will be useful for the selection of expansion joints in the design process.     

基于软化拉-压杆模型的RC空间边节点抗剪承载力计算方法

实际地震作用是多维的、随机的,框架节点在2个方向同时受力,其抗震能力相比于单向地震作用会降低。目前,对节点核心区在2个方向同时受力时抗剪承载力的研究尚未完善。在双向受力下,节点核心区2个方向传来的剪力形成合剪力作用面,在节点核心区内部形成不同于单向受力下的斜向斜压杆。本文基于软化拉-压杆模型,针对水平双向受力相同的空间边节点,在合剪力作用面内建立抗剪承载力计算模型,确定空间边节点核心区斜压杆以及钢筋拉杆的计算方法。利用有限元软件建立不同参数空间边节点模型,并收集部分空间节点试验数据,将剪力计算值与模拟值或试验值进行对比。结果表明,基于软化拉-压杆模型建立的双向受力下钢筋混凝土框架,其边节点抗剪承载力计算值与模拟值或试验值吻合良好。     

FRP抗震加固混凝土梁柱节点的受剪承载力分析

通过采用SGFRP、HFRP加固的四个混凝土梁柱节点在低周反复荷载作用下的抗震性能对比试验研究,提出了FRP加固节点受剪承载力的计算公式,并基于分析给出了相关计算参数的工程设计建议取值,并对加固方式、纤维品种、纤维粘贴角度等主要因素对节点抗剪承载能力的影响机理进行了分析,结果表明:在节点核心区和梁柱端头粘贴纤维可以有效的提高节点的受剪承载能力;加固方式直接影响节点受剪承载能力的大小。