利用能量法的边坡强度参数反演研究

强度参数反演是获取岩土工程参数的重要手段之一。传统的位移反分析方法需要对岩土体进行位移监测,耗费较多的时间和资金。本文在极限分析上限定理的基础上进行安全系数的求解。并分析边坡的几何及参数连续性,将边坡破坏断面两侧的断面的安全系数视为1。通过做出不同断面的c—φ曲线,其曲线的交点即为反演所得的参数值。结果表明,其结果与试验值符合较好,效果较好。     

京沪高铁天津西站曲线变宽异型钢箱梁设计实践

在恒载、温度荷载和活载等因素作用下连续曲线钢箱梁会出现支座脱空、梁体侧移和翻转等问题。同时相对直梁桥,弯桥扭转效应明显,应引起重视。该文通过京沪高铁天津西站异型连续曲线钢箱梁的设计实践,探讨该类桥梁设计中应注意的若干问题,使连续曲线钢箱梁设计安全、合理、经济。     

站桥同位合建上盖钢箱梁“π”形支架门吊架设技术

为了解决繁华城区既有道路有限空间内快速、安全架设小半径曲线钢箱梁的施工难题,依托地铁车站柱网形式及围护结构冠梁为基础,采用高位门吊及"π"形支架体系架设方案,实现了在空间受限情况下,地铁车站、市政道路及高架桥三者的和谐统一。以合肥南北高架一号线Ⅰ标明挖地铁芜湖路站及其同位合建的上盖小半径反曲线钢箱梁为例,阐述站桥同位合建理念及"π"形支架联合门吊架梁方案,并对架梁支架及架梁对地铁车站的影响进行力学分析。得出以下结论:1)站桥同位合建共用一个走廊,既减少拆迁,又节约投资,为繁华城区有限空间立体开发提出了解决思路;2)利用下卧地铁车站柱网及桩顶冠梁,"π"形支架联合门吊架设,支架简单可靠、门吊快速安全,平行流水作业,安全、快速、经济,很好地克服了"S"形小半径反向曲线反超高的空间扭曲结构曲线拟合难、安全风险大的困难;3)"π"形支架支撑体系利用了下部车站柱网结构,能满足安全性要求。     

California’s Low Carbon Fuel Standard: Modeling financial least-cost pathways to compliance in Northwest California

The transition to low-carbon transportation fuels plays a key role in ongoing efforts to combat climate change. This analysis seeks to optimize potential alternative fuel portfolios that would lead to a 10% reduction in fuel carbon intensity by 2020 as required under California’s Low Carbon Fuel Standard (LCFS).We present a novel, probabilistic modeling approach for evaluating alternative fuel portfolios based on their marginal greenhouse gas (GHG) abatement costs. Applied to a case study region in Northwest California, our model enables us to quantify the financial cost of GHG reduction via each fuel pathway, as well as for a portfolio deployed to meet the LCFS target. It also enables us to explore the sensitivity of the alternative fuel portfolio, evaluating the impact of fluctuating prices, fuel carbon intensities, and technology penetrations on the makeup of the portfolio and on the average cost of GHG abatement.We find that battery electric vehicles play a critical role, as they offer the lowest-financial-cost significant abatement in almost all plausible scenarios. However, electric vehicles alone will not be sufficient to reach the target; low-carbon biofuels can be expected to play a role in the achievement of 2020 Low Carbon Fuel Standard targets.     

A framework for estimating traffic emissions: The development of Passenger Car Emission Unit

In this study, we develop a Passenger Car Emission Unit (PCEU) framework for estimating traffic emissions. The idea is analogous to the use of Passenger Car Unit (PCU) for modeling the congestion effect of different vehicle types. In this approach, we integrate emission modeling and cost evaluation. Different emissions, typically speed-dependent, are integrated as an overall cost via their corresponding external costs. We then develop a normalization procedure to obtain a general trend that is applicable for all vehicle types, which is used to derive a standard cost curve. Different vehicle types with different emission standards are then mapped to this standard cost curve through their corresponding PCEUs that are to be calibrated. Once the standard cost curve and PCEUs have been calibrated, to estimate the overall cost of emission for a particular vehicle, we only need to multiply the corresponding PCEU of that vehicle type to the standard cost curve. We apply this PCEU approach to Hong Kong and obtain promising results. Compared with the results obtained by the full-blown emission model COPERT, the approach achieves high accuracy but obviates tedious inputs typically required for emission estimation.     

An analytical SCF solution method for joint misalignments and application in fatigue test data interpretation

In this study, we first present a general analytical method for calculating stress concentration factors in a cruciform connection containing either axial or angular misalignment between two intercostal members through an application of Castigliano's second theorem. As such, various end restraint conditions of interest in practice can be considered with ease. Such a solution method provides stress concentration factors at intersection location not only with respect to intercostal members, but also with respect to continuous members. A comprehensive set of SCF solutions, confirmed by finite element solutions, are then presented in tabular forms which can be used as supplements to the existing SCF solutions such as those given in BS 7910 and DNV-RP-C203 for performing fatigue and fracture assessment of welded connections. Some of the existing solutions are shown to be valid only under a narrower set of conditions than documented and some seem to be in significant error. As a further demonstration of the validity of the analytical approach presented in this paper, the same analytical formulation is applied for examining interaction effects between misalignments and fatigue testing conditions, resulting in significantly improved correlation of fatigue test data obtained as a part of this study.     

乳化沥青冷再生混合料疲劳性能研究

采用目前工程上常用的两档沥青路面铣刨旧料对RAP掺量为80％和100％的乳化沥青冷再生混合料进行材料组成设计.通过击实试验和劈裂试验分别确定其最佳流体含量和最佳乳化量用量.在配合比设计基础上采用控制应变加载模式对乳化沥青冷再生混合料疲劳性能进行试验研究,确定了加载较为合理的应变水平,即300,250,200με和150με.试验结果表明,在应变水平较高时,两种RAP掺量下乳化沥青冷再生混合料能承受有限的荷载作用次数,当应变水平降低到150 μe时,两种RAP掺量混合料在150万次荷载作用下仍未破坏,采用劲度模量与荷载作用次数预估的方法确定了疲劳寿命.通过对4种应变水平-荷载作用次数进行疲劳曲线拟合,提出两种RAP掺量下乳化沥青冷再生混合料的应变控制指标.     

不同交通方式的道路利用效率测度方法

道路交通拥堵问题的根本原因之一是交通量与道路面积之间的矛盾,而如何从微观角度定量测度不同交通方式的道路利用效率,尚没有成熟、公认的方法。围绕不同道路交通方式的客运周转量与运输过程占用的道路面积之间的关系,提出一种定量分析不同交通方式道路利用效率的测度方法。该方法反映了不同交通方式的载客量、运输距离、运输速度、运输过程的占路面积和占路时间等要素对道路交通的影响和作用机理。基于天津市区GPS车辆行驶数据,以小汽车、"步行+公交"出行方式为例,具体阐述该测度方法的应用。结果显示,完成同样运输量,小汽车道路占用面积是公共汽车的7倍。     

一种复杂载荷作用下船舶结构疲劳裂纹扩展预报方法

风暴模型是Tomita等提出的用来评估船舶结构疲劳强度的一种随机波浪载荷简化模型,它能表达波浪载荷是与时间相关的随机过程。文中介绍了风暴模型及波浪诱导应力短期分布的基本特征。将风暴模型和裂纹扩展率单一曲线模型及焊趾表面裂纹应力强度因子的计算方法结合起来,探讨了复杂载荷作用下船舶结构疲劳裂纹扩展预报方法。并用权函数法计算了给定残余应力分布的表面裂纹应力强度因子。预报了对接焊接接头焊趾处表面裂纹在风暴波浪载荷作用下的疲劳裂纹扩展行为,结果表明风暴的大小、顺序,初始裂纹尺寸及残余应力对裂纹扩展行为影响明显。合理的风暴模型参数及初始裂纹尺寸的确定对船舶结构的疲劳寿命预报是非常重要的。     

空腹式连续刚构桥设计参数的正交试验研究

为研究空腹式连续刚构桥结构设计参数的优化,以某主跨290m的空腹式连续刚构桥为背景工程,通过有限元分析软件建立其结构模型,采用正交试验方法,研究空腹段梁底曲线幂次、下弦梁高以及根部梁高等设计参数取值对结构经济性的影响。结果表明:空腹段梁底曲线幂次对结构经济性影响显著,且根部梁高取主跨跨径的1/8、梁底曲线幂次取2.75、下弦梁高取主跨跨径的1/50为最优的结构设计参数。