Improved Evaluation of Equivalent Top-Down Load-Displacement Curve from a Bottom-Up Pile Load Test

A modified procedure is presented in this study to evaluate the equivalent top-down load-displacement curve in a bottom-up pile load test considering elastic shortening. On the basis of the results of a parametric study on a bored pile in normally consolidated cohesive soils under undrained conditions, varying shear strength distribution and pile slenderness ratio, it was concluded that the pile shortening caused by the skin-friction component of the load in a top-down test can be related to the measured elastic shortening in a bottom-up test. A λ-factor is used to define this relationship, that is, the ratio of the top-down to bottom-up pile shortening. The factor λ = 1.0 is used for the case of a pile in soil with uniform shear strength profile, λ = 2.0 for linear profiles, 1.0<λ<2.0 for nonlinear profiles varying above linear, and λ>2.0 for nonlinear profiles varying below linear. In addition, the method suggests taking the corresponding readings of the skin-friction load component from the upward displacement curve of the top of the pile, which is a closer approximation to rigid pile displacement than the bottom when corrections for elastic pile shortening are to be applied. Assuming a fully mobilized skin-friction, a logarithmic relation for the factor λ to the normalized area under the shear strength profile was generally formulated and is limited to the assumptions on which they were derived. The suggested procedure in this study has produced the equivalent top-down load-displacement curves that are in close agreement with the measured top-down curve, as validated in the case studies.     

Six d.o.f. displacement measuring device based on a modified Stewart platform

Acquisition of the displacements and deformations of a loaded component is generally a not easy operation. This is especially the case as the component often presents a complex geometry and the deformations involve more degrees of freedom or a combination of them.Measurement devices used for this kind of application often allow to obtain simplified measurements.This paper presents a novel measurement device, consisting of six displacement sensors mounted as a parallel mechanism, capable to measure the global deformation of a component in terms of translations and rotations. The deformations are obtained by applying the direct kinematic equations to convert the six displacements read from the six sensors into the three translations and rotations representing the deformation of the component.The geometry of the device leads to write simplified equations for the direct kinematic that can be solved with a semi-numerical procedure implemented in a program written in Matlab environment.The results given by this procedure have been validated with the positions obtained from a 3D CAD model of the device, showing perfect agreement between the results.A prototype has been made and tested on a workbench.     

车路互联网的底层协议-802．11p标准

详细地描述了车路互联网系统的底层协议-802．11p标准。将802．11p与传统无线局域网技术进行对比,分析了802．11p在媒体接入控制层（MAC）与物理层（PHY）所做的修改,并从物理层参数、PP—DU帧结构,以及接人优先级等多方面指出了802．11p能在高速移动环境下建立稳定通信链路的原因。其次,还对802．11p所采用的频段、信道、发射功率以及频谱掩模进行分析;最后提出了802．11p在仿真方面所面临的挑战,并且在Simulink上建立了一套动态仿真系统,对标准进行仿真验证。     

Discrete fracture in high performance fibre reinforced concrete materials

In this paper a simple, but effective methodology to simulate opening mode fracture in high performance fibre reinforced concrete is presented. The main contribution of the paper is a technique to extrapolate the load displacement curves of three point bending experiments on fibre reinforced concrete. The extrapolation allows the full work of fracture to be determined, from which the fracture energy may be obtained. The fracture energy is used in the definition of a cohesive softening function with crack tip singularity. The softening relation is implemented in an embedded discontinuity method, which is employed for the numerical simulation of three point bending experiments. The experimental work includes a size effect study on three point bending specimens. The numerical simulation provides a satisfactory prediction of the flexural behaviour and the size effect observed in the experiments.     

加膜冷却顶板/置换通风系统及其实验研究

对冷却顶板/置换通风系统中存在的两个突出问题:冷却顶板易“结露”以及形成“下降气流”破坏置换通风的流型进行理论分析,提出了用对长波具有高透过性的薄膜包裹冷却顶板,在冷却顶板下表面和薄膜之间保留真空或空气夹层的解决方法,并且设计了实验系统,选定了长波高透过性薄膜作为实验材料,通过实验对新系统的性能进行了验证.结果表明:在外界环境基本相同的条件下,加装长波高透过性薄膜后,冷却顶板/置换通风系统的室内温度略有升高,平均升高1.8％;污染度明显下降,在呼吸区以下,平均降低60％;在呼吸区以上,平均降低40％,空气品质明显得到了提高.     

程潮铁矿东区地表及井筒变形监测分析

针对程潮铁矿东区地表及构筑物开裂变形日趋严重的问题,采用GPS、水准仪和数字裂缝计开展了高精度的地表三维变形和井筒裂缝变形的监测工作.根据现场接近两年实测的东区地表位移和两主井井筒裂缝变形数据,分析了矿区地表及井筒变形规律和趋势.结合场地工程地质条件、采矿情况等,对监测结果出现的水平位移波动、裂缝闭合、区域变形差异等几...     

大型热模锻压力机机架组件有限元分析

以某热模锻压力机机架组件为研究对象,对组件建立有限元模型.通过对机架加载,对机架进行有限元分析,并研究压力机机架的位移和变形量.该研究对热模锻压力机机架组件的设计和应力分析提供重要的理论数据,具有一定的推广应用价值.     

基于单总线的小环境温度监测系统研究

针对目前小环境温度监测系统的现状,介绍了单总线技术和DS18B20数字式传感器的特点。以AT89C51单片机为核心控制部件,结合小环境温度控制系统的要求,设计了基于单总线技术的小环境温度监测系统,并给出了该监测系统的硬件结构和进行了相应的软件设计。从实际应用结果表明,该系统具有测量精度高、抗干扰性强、可靠性高和性价比好等特点,在工程实际应用中具有重要意义。     

相控阵超声检测系统特性评价的具体要求（一）

超声相控阵技术对缺陷的检出能力,对缺陷定位、定量、定性表征的准确性,相关于相控阵仪器和系统特性的综合功能。本文介绍ASMEBPVC（美国锅炉压力容器法规）最新版（2009增补）有关相控阵超声检测仪器和系统特性评价的具体要求,包括相控阵：（1）声柬轮廓的测定;（2）声柬变角范围的测定;（3）阵元激活性的测定;（4）聚焦能力的测定;（5）参数和数据显示的计算机控制;（6）探头楔块衰减和延迟补偿的评价：（7）仪器垂直线性和水平线性及动态范围的评价。期望为国内承压设备相控阵超声检测的有效应用和标准化,提供法定依据和有用借鉴。     

基于Linux操作系统进程迁移系统设计

对已有的经典算法进行分类对比,选择了具有较高迁移速度和对源节点没有残余依赖性的Total-copy算法,基于选择的算法,把迁移系统分为Manager模块、MigrateOut模块和MigrateIn模块等三个模块,并给出了主要模块的实现流程图、设计原理和实现过程。