预制双裂纹板岩各向异性细观尺度实验研究

 板岩是一种非均质、连续–非连续介质,包含有微裂隙、微孔洞和微构造等,在力学、渗流、热传导等诸多方面均表现出明显的各向异性。选取锦屏水电站辅助洞泥质板岩试样,采用超薄金刚石锯片在标准岩样上预制一对三维裂纹,并应用岩土CT实验技术,开展水平和垂直层理方向加载条件下裂纹演化的细观尺度观测,分别得到了天然和预制双裂纹板岩破坏过程的细观表现特征,对比分析了水平和垂直层理方向加载条件下板岩裂纹起裂、扩展和破坏模式的不同,并对基于密度统计的岩石细观损伤变量定义方法的局限性进行了分析和讨论,为研究板岩的力学各向异性提供了新思路。     

Effects of lateral unloading on the mechanical and deformation performance of shield tunnel segment joints

Unloading during lateral excavation widely occurs in existing subway shield tunnels. Previous studies have focused on the overall stress and deformation of existing tunnels caused by nearby unloading. However, the stress and deformation state of tunnel segment joints have yet to be considered. This study considered the non-continuity of the shield tunnel lining and the interactions among tunnel segment, surrounding rocks and ballast bed. A hybrid model of a shield tunnel was established based on 3D nonlinear contact theory. The mechanical and deformation properties of the segments and joints of an existing shield tunnel under the influence of lateral excavation of the foundation pits were studied. Unloading during lateral excavation caused the cross section of the shield tunnel to generate vertical convergence and shift horizontally towards the foundation pit. An opening and dislocation in the joint, which caused the waterproof ability of the joint to decrease sharply, were observed. Meanwhile, stress at the segment joint increased sharply and caused local cracks in the segment lining. Axial and shearing force on the joint bolt also increased significantly. Based on existing subway regulations, the calculation results were combined to establish a deformation control standard for existing shield tunnels under lateral excavation. The rate of vertical convergence of the lining should be less than 3.68‰, and the rate of horizontal shift of the axis should be less than 0.53‰.     

Verbundverhalten von Vollgewindeschrauben in Brettschichtholzbauteilen

Bond behaviour of self‐tapping screws being used as reinforcement in glue‐laminated timber elements – Part 2: Analytical and numerical investigations as well bond model derivation for the calculation of anchorage length In favor of the investigation of bond behaviour, force transfer and anchorage length of self‐tapping screws, several tests have been realized at the Chair of Structures and Structural Design in cooperation with the Institute for Building Material Research of the RWTH Aachen University. The experimental investigations comprise more than 160 pull‐out tests of screws with long embedment length and over 84 load distributions tests. Additionally, several tests displaying the effect of longitudinal cracks in the surrounding wood as well as the effect of the screw tip have been conducted. Through various analyses of the bond behaviour, the experimental investigations form the basis for the calibration and evaluation of the numerical models and allow a prediction of the force transfer of the screws in glue‐laminated elements. Design rules that enable the application of the self‐tapping screws as reinforcement in timber elements have been derived from the knowledge obtained in the experimental and numerical investigations. This paper, which results from a research project funded by the German Research Foundation [1], presents the results of investigations on the bond behavior of self‐tapping screws in glue‐laminated timber elements. Part 1 elaborates on the experimental investigations [2] whereas part 2 illustrates the numerical analyses and presents a bond model, which enables the design of the anchorage length and the safe application of the screws as reinforcement in timber elements.     

Design Signals: The Role of Software Architecture and Paradigms in Design Thinking and Practice

Does the ontology of design software influence built form? Panagiotis Michalatos , lecturer in architectural technology at Harvard Graduate School of Design and a principal research engineer at Autodesk, Inc, here looks at how the move from drawing typologies to digital modelling since the mid-1990s has affected architectural aesthetics. He goes on to examine two more recent developments that may announce a further paradigm shift: granular tracking of design input, and data organisation practices in biomedics which, transferred to architecture, could allow for a more spatio-temporal approach.     

基于CT图像的混凝土单轴压缩裂隙与应变场分析

利用X射线计算机层析术(CT)对混凝土试件单轴压缩过程进行原位扫描,获得了不同荷载下试件的CT图像.通过对CT图像进行分析,获得了灰度均值及其均方差、孔隙率和计盒维数随荷载变化的规律.结合数字体散斑法(DVSP)获得了试件内部三维位移场与应变场.结果表明:试件内部不同尺度裂隙的发展导致灰度均值及其均方差、孔隙率和计盒维数发生相应的变化,灰度均值及其均方差可以揭示小于CT尺度裂隙的发展规律,孔隙率和计盒维数更适用于描述大于CT尺度裂隙的特征.试件内部的位移场与应变场能够直观地揭示出小于CT尺度微裂隙引起的应变局部化区域的产生及发展过程,为混凝土细观破坏机理研究提供了新方法.     

地面出入式盾构隧道受力变形特性数值分析

地面出入式盾构隧道(GPST)是一种不需要工作井的新型盾构工法,在国内首次应用于南京地铁。盾构机从地面直接出发,隧道所受荷载与一般隧道有很大区别,传统的惯用法是否适用尚存疑问,因此需要进一步研究隧道的受力变形特性。本文以地面出入式盾构施工过程中出现的负覆土—零覆土—浅覆土工况作为研究对象,建立精细化隧道三维模型,分析隧道在不同覆土厚度工况下的受力变形规律,并获得相应的横向刚度折减系数。同时针对土体侧向土压力系数K₀进行参数分析,揭示不同地层条件下隧道收敛变形的变化规律。研究表明,横向刚度折减系数随覆土深度增加而增加,而且随着覆土厚度的增加,变形模式由“横鸭蛋”变为“竖鸭蛋”的临界K₀系数值逐渐增大。     

三维数字航道的设计与实现

针对我国内河航道水深季节变化大、航行安全要求高的特点,本文运用虚拟现实、三维地理信息系统、计算机图形图像处理等技术,对三维航道数据库、水下地形建模及疏浚分析、水体可视化、实时水位可视化、航标建模及可视化等关键技术进行攻关,并以长江重庆航道示范段为例,建立三维数字航道系统,支持实时航标、船舶、水位信息集成。本文在推进航道精细化管理、增强水上安全方面具有重要作用。     

基于FLAC3D主动土压力数值模拟比较研究

运用岩土工程三维有限差分软件FLAC3D,分别在Mohr-Coulomb、Elastic和Drucker-Prager三种岩土本构模型下,对作用在支挡结构上的主动土压力进行数值模拟,并与朗金土压力理论计算方法进行比较,比较研究FLAC3D中不同模型的选择对分析结果的影响,为研究主动土压力问题时合理选择本构模型等数值模拟关键技术问题提供参考。     

南京林业大学新庄站换乘空间现状分析与优化设计

我国的城市化进程不断加快,各大城市的轨道交通也在如火如荼的建设之中。故建立良好的自行车与城市轨道交通换乘系统(B+R系统)是极有必要的。[1]本文通过对南京地铁3号线南京林业大学新庄站点与自行车换乘空间的实地调研,分别从外部空间、停车空间、交通换乘空间、附属空间、景观空间进行调查。归纳现场调研信息、总结分析结果、提出改造空间,使空间利用最大化的建议,以提升街道景观质量和自行车停车效率。