隧道工程耐久性施工的关键技术

研究目的:目前隧道施工对于混凝土结构主要考虑结构的承载能力,而较少考虑环境作用引起的材料性能恶化对混凝土耐久性带来的影响。混凝土的耐久性不足,不仅会增加使用过程中的修理费用,影响工程的正常使用,而且会过早地结束结构的使用年限,造成严重的资源浪费。因此,以后的隧道施工应对混凝土的耐久性引起高度重视。研究结果:合理的混凝土配合比,优质的原材料,可靠的施工过程质量控制(拌和、运输、浇筑、振捣等方面),以及混凝土的合理养护是确保混凝土结构耐久性的主要因素,也是隧道工程耐久性施工的关键技术。     

考虑群体异质性的建成环境与老年人慢行出行关系研究

健康老龄化背景下，慢行出行是提升老年人身心健康、生活品质的重要方式，而建成环境是影响老年人慢行出行的重要因素。本文以2013年南京市老年人出行实测数据为基础，利用潜在类别聚类方法对老年群体进行异质性分析，分类建立随机森林模型研究建成环境指标对不同老年群体慢行出行时间的重要度影响及两者之间的非线性关联。研究结果表明：以性别、是否退休、学历、家庭收入以及学龄前儿童这5个类别变量作为外显变量，可将老年群体划分成两类，各自建立的老年人慢行时间模型整体拟合优度较好；其中，影响第1类老年群体的关键建成环境变量有慢行路网密度、交叉口数和地铁站邻近度，第2类老年群体慢行出行时间的影响因素主要有地铁站邻近度、慢行路网密度和住宅密度，另外同一建成环境指标对两类老年群体慢行出行时间的非线性关联也不相同。研究结果可为制定差异化的老年宜居环境优化政策，提升老年人生活品质以及实现健康老龄化提供理论依据。     

船体主要载荷效应的随机组合

基于静水载荷的时间变异性，导出了一种静水载荷效应与波浪载荷效应组合的新方法，同基于FBC（Ferry Borges Castenbete）模型或随机过程的上跨率的组合形式相比较，此方法的概念更清晰，计算更容易实施，考虑到规范中给定的最大允许静水载荷效应对应的普遍接受的超越概率水平，以及静水载荷过程跨越某一固定水平的概率的上界特性，规定静水载荷过程超越二十年最大允许载荷效应的概率为确珲载荷效应特征值的概率水平，经过这样处理，避免了载荷效应特征值的过高估计，通过数值分析检验方法的有效性，结果表明本文的方法可以得到级合载荷效应特征极值的一致估计。     

滑坡致环境镉污染的研究

调查发现山体滑坡引起天然水镉污染，源水镉的含量为０．５７～３．８８ｍｇ／Ｌ，下游水体、鱼类、土壤、农作物受到严重污染，人群健康受到镉危害。水镉污染稀释迁移规律曲线拟合方程呈双曲线，土壤和大米含量均高于对照区，血镉、尿镉和尿β２－ＭＧ水平与对照区比较明显升高，人群镉摄入量与尿镉排泄量呈正相关关系，血、尿镉和尿β２－ＭＧ三项指标间的二联指标阳性率明显高于对照区。     

两种不同夯击能地基处理效果对比分析

某场地地基加固处理拟采用强夯法,大面积施工前为确定合理的强夯参数,选取2个试验区进行2种不同夯击能的强夯试验。通过对2个试验区地基处理后的效果检验,对比分析2种方案地基处理后的夯沉量、遍夯间隔时间、强夯影响深度和地基处理效果,为最终的方案选取和同类场地的强夯法地基处理提供参考。     

Simulating pedestrian movements at signalized crosswalks in Hong Kong

This paper presents a new pedestrian simulation (PS) model for signalized crosswalks in Hong Kong. This PS model is capable of estimating the variations of walking speed particularly on the effects of bi-directional pedestrian flows so as to determine the minimum required duration of pedestrian crossing time. Video records taken from the observational surveys at the selected crosswalk in urban area were used to extract the required data for model calibration. It was found that the design walking speed for signalized crosswalks should be varied by the effects of the bi-directional pedestrian flows. It was also interesting to note that the negative impact of the bi-directional flow effects (ranging from uni-directional to bi-directional pedestrian flows) on the chance of pedestrian crossing the crosswalk is increasing from free-flow to at-capacity flow conditions. The new PS model is also validated using an independent data set so as to examine the reliability of the simulation results. The validation results show that the new PS model can provide an accurate evaluation on the changes of walking speed and its standard deviation under different scenarios with particular emphasis on the effects of the bi-directional pedestrian flows. The advancement of this PS model can be applied to assess the effects of each improvement measure and to evaluate the benefits of each scenario in practice.     

充分发挥海事管理机构在建桥监管工作中的作用

近年来，桥梁建设安全问题已越来越受到社会的关注，海事管理机构在桥梁建设过程中，不仅在人力、物力和财力上作出了大量投入，而且在水上安全监管工作中也做了大量有益的工作，文中就如何充分发挥海事管理机构在建桥监管工作中的作用，从前期介入、及早布置、扩大宣传、科学监管、隐患排查等方面对建桥水上安全监管工作进行分析．希望能够对建桥监管工作有所帮助。     

Characterization and prediction of air traffic delays

This paper presents a new class of models for predicting air traffic delays. The proposed models consider both temporal and spatial (that is, network) delay states as explanatory variables, and use Random Forest algorithms to predict departure delays 2–24 h in the future. In addition to local delay variables that describe the arrival or departure delay states of the most influential airports and links (origin–destination pairs) in the network, new network delay variables that characterize the global delay state of the entire National Airspace System at the time of prediction are proposed. The paper analyzes the performance of the proposed prediction models in both classifying delays as above or below a certain threshold, as well as predicting delay values. The models are trained and validated on operational data from 2007 and 2008, and are evaluated using the 100 most-delayed links in the system. The results show that for a 2-h forecast horizon, the average test error over these 100 links is 19% when classifying delays as above or below 60 min. Similarly, the average over these 100 links of the median test error is found to be 21 min when predicting departure delays for a 2-h forecast horizon. The effects of changes in the classification threshold and forecast horizon on prediction performance are studied.     

Influence of mesh size,stress triaxiality and damage induced softening on ductile fracture of large-scale shell structures

In this investigation, ductile fracture in stiffened and unstiffened panels is simulated employing the fracture criterion, which depends on the mesh size, stress state and damage induced softening. The aim of the study is to show that employed fracture criterion removes mesh size effects more efficiently than traditional fracture criteria adjusted only on the basis of uniaxial tension. Fracture model is implemented into Finite Element software ABAQUS using user-defined material, VUMAT-subroutine, available for shell elements. Mesh size sensitivity analysis is carried out. Finite element simulation results are validated with experimental measurements available in literature. Comparison of numerical and experimental results shows that simulations effectively capture most of the experimentally observed features, especially when considering different mesh densities. In most cases, mesh size effects are considerably reduced compared with the fracture criteria adjusted on the basis of a uniaxial tension.     

行波效应对大跨度连续刚构桥地震反应的影响

利用大型结构分析程序ANSYS／TRANSIENT，对地震波三向正交分量独立作用和联合作用下连续刚构桥的地震反应的行波效应进行了时程分析的数值模拟，分析了连续刚构桥在各向振动分量的作用，以及各向振动不同相位差的行波效应，对其地震反应的一般影响规律进行了讨论。结果表明：在地震波的各单向行波效应和三向正交行波效应时，结构的内力均有不同程度的增大，而结构的位移却呈现减少的趋势，结构的振动周期延长。