沥青混合料转运车作业质量

论述了传统沥青混凝土路面施工工艺存在的缺陷及其原因,确定了沥青混合料转运车作业质量试验的目的、意义及试验研究的内容和方法,以工程施工实践证明了转运摊铺施工工艺可以有效减少混合料材料离析和温度离析现象,同时能提高铺设成型路面的平整度.     

混凝土箱梁设计参数对温度效应的影响

在对水府庙混凝土箱梁桥温度场的实测和分析基础上,进行设计参数的研究,包括箱梁翼缘悬臂长度、腹板高度和桥梁轴线方位角对温度场和温度应力的影响,得到最大横向温差与（腹板高度/翼缘悬臂长度）的曲线图.     

大跨径连续刚构桥的温度效应分析

以魏家洲特大桥为例,按照我国公路桥涵设计规范、英国BS5400规范、新西兰规范确定不同的计算模式,对大跨径连续刚构桥进行温度效应分析,得出：温度应力在大跨径连续刚构桥整个桥梁设计中占有很大的比重,且采用不同的温度梯度计算模式,所得到的梁内温度应力值相差较大,甚至出现异号的温度应力.     

沥青混凝土转运车对提高道路施工质量的试验研究

对道路摊铺过程中采用摊铺机直接摊铺作业和采用徐工AT1000A型转运车与摊铺机联合施工作业的试验路面效果进行了对比,分析了摊铺温度场和骨料摊铺效果.结果证明使用沥青混凝土转运车是提高道路施工质量的有效手段.     

Fitness-for-purpose assessment of cracked offshore wind turbine monopile

In this paper, the procedure for flaw acceptability assessment is examined through a case study of a semi-elliptical surface crack in an offshore monopile as it grows till it forms a through thickness crack. Using the procedure prescribed in an industrial standard (BS 7910), the fracture ratio, K_r is shown to increase monotonically with increasing crack depth. The load ratio, L_r, is initially insensitive to the crack depth. However, there is a rapid increase in L_r when the crack depth to thickness ratio exceeds 80%. L_r values obtained from detailed 3D FE limit analysis using elastic-perfectly-plastic material behaviour do not exhibit the asymptotic behaviour predicted by BS 7910 as the flaw transitions from deep crack to through-thickness crack. Furthermore, K_r predicted by BS 7910 is shown to be an over-estimation for the typical dimensions of offshore monopiles. The findings suggest that a structure with a deep flaw may be identified as unacceptable based on BS 7910 when it may still possess a non-trivial amount of structural residual life. This is a concern for monopiles where crack growth as a large flaw forms a significant part of the total life.     

多年冻土区钻孔灌注桩施工过程热力特性研究

钻孔灌注桩水化热会暖化冻土引起桩基承载力下降,以桩基水化热在时间与空间上的影响效应为研究目的,结合青藏公路G214沿线查拉坪旱桥桩基观测数据,分析水化热对地温场的扰动范围以及桩周土回冻时间,给出灌注桩18 d内的养护温度。结果表明:水化热对距桩1.95 m以外地温影响微弱;144 d后桩侧温度降至0℃以下,229 d后桩侧温度低于-0.5℃;2 a后桩侧基本回冻至天然地温,此时承载力已达到设计要求。桩基混凝土养护温度前5 d在10℃以上,5~12 d在5℃以上,12~15 d为2℃以上,15~18 d仍高于0℃。通过数值仿真给出混凝土入模温度及桩基施工时间对桩周温度场的影响,模拟结果显示,该区域的灌注桩施工可以在相应规范规定范围内提高混凝土入模温度;灌注桩施工可以在冷季进行,但要做好5 m以上深度桩基混凝土的温控措施。     

Travel time estimation from sparse floating car data with consistent path inference: A fixed point approach

Estimation of urban network link travel times from sparse floating car data (FCD) usually needs pre-processing, mainly map-matching and path inference for finding the most likely vehicle paths that are consistent with reported locations. Path inference requires a priori assumptions about link travel times; using unrealistic initial link travel times can bias the travel time estimation and subsequent identification of shortest paths. Thus, the combination of path inference and travel time estimation is a joint problem. This paper investigates the sensitivity of estimated travel times, and proposes a fixed point formulation of the simultaneous path inference and travel time estimation problem. The methodology is applied in a case study to estimate travel times from taxi FCD in Stockholm, Sweden. The results show that standard fixed point iterations converge quickly to a solution where input and output travel times are consistent. The solution is robust under different initial travel times assumptions and data sizes. Validation against actual path travel time measurements from the Google API and an instrumented vehicle deployed for this purpose shows that the fixed point algorithm improves shortest path finding. The results highlight the importance of the joint solution of the path inference and travel time estimation problem, in particular for accurate path finding and route optimization.     

内压载荷下X80管道裂纹应力分布规律研究

为了研究内压作用下管道裂纹应力场分布规律,以含有表面裂纹的X80管道为研究对象,对不同形状、不同方向、不同内压、不同尺寸的含裂纹管道进行仿真分析和实验验证。结果表明:裂纹尖端处应力远大于裂纹中心应力。裂纹形状对应力影响作用较小,随着裂纹方向与管道轴向夹角增大,裂纹尖端应力先增大后减小,随着管道内压、裂纹深度、裂纹长度的增大,裂纹尖端处应力随之线性增大。其中,裂纹长度对裂纹尖端应力的影响小于管道内压和裂纹深度。     

A generic data assimilation framework for vehicle trajectory reconstruction on signalized urban arterials using particle filters

With trajectory data, a complete microscopic and macroscopic picture of traffic flow operations can be obtained. However, trajectory data are difficult to observe over large spatiotemporal regions—particularly in urban contexts—due to practical, technical and financial constraints. The next best thing is to estimate plausible trajectories from whatever data are available. This paper presents a generic data assimilation framework to reconstruct such plausible trajectories on signalized urban arterials using microscopic traffic flow models and data from loops (individual vehicle passages and thus vehicle counts); traffic control data; and (sparse) travel time measurements from whatever source available. The key problem we address is that loops suffer from miss- and over-counts, which result in unbounded errors in vehicle accumulations, rendering trajectory reconstruction highly problematic. Our framework solves this problem in two ways. First, we correct the systematic error in vehicle accumulation by fusing the counts with sparsely available travel times. Second, the proposed framework uses particle filtering and an innovative hierarchical resampling scheme, which effectively integrates over the remaining error distribution, resulting in plausible trajectories. The proposed data assimilation framework is tested and validated using simulated data. Experiments and an extensive sensitivity analysis show that the proposed method is robust to errors both in the model and in the measurements, and provides good estimations for vehicle accumulation and vehicle trajectories with moderate sensor quality. The framework does not impose restrictions on the type of microscopic models used and can be naturally extended to include and estimate additional trajectory attributes such as destination and path, given data are available for assimilation.     

Estimating traffic volumes for signalized intersections using connected vehicle data

Recently connected vehicle (CV) technology has received significant attention thanks to active pilot deployments supported by the US Department of Transportation (USDOT). At signalized intersections, CVs may serve as mobile sensors, providing opportunities of reducing dependencies on conventional vehicle detectors for signal operation. However, most of the existing studies mainly focus on scenarios that penetration rates of CVs reach certain level, e.g., 25%, which may not be feasible in the near future. How to utilize data from a small number of CVs to improve traffic signal operation remains an open question. In this work, we develop an approach to estimate traffic volume, a key input to many signal optimization algorithms, using GPS trajectory data from CV or navigation devices under low market penetration rates. To estimate traffic volumes, we model vehicle arrivals at signalized intersections as a time-dependent Poisson process, which can account for signal coordination. The estimation problem is formulated as a maximum likelihood problem given multiple observed trajectories from CVs approaching to the intersection. An expectation maximization (EM) procedure is derived to solve the estimation problem. Two case studies were conducted to validate our estimation algorithm. One uses the CV data from the Safety Pilot Model Deployment (SPMD) project, in which around 2800 CVs were deployed in the City of Ann Arbor, MI. The other uses vehicle trajectory data from users of a commercial navigation service in China. Mean absolute percentage error (MAPE) of the estimation is found to be 9–12%, based on benchmark data manually collected and data from loop detectors. Considering the existing scale of CV deployments, the proposed approach could be of significant help to traffic management agencies for evaluating and operating traffic signals, paving the way of using CVs for detector-free signal operation in the future.