一种基于灵敏度矩阵进行桥梁损伤识别的方法

重点研究了一种基于灵敏度矩阵对桥梁进行损伤识别的方法。基于振动分析的矩阵摄动理论,首先讨论了求取模态参数对结构物理参数灵敏度矩阵的方法,形成灵敏度矩阵的过程中避免了偏微分计算;基于灵敏度矩阵,建立了桥梁的损伤识别模型,并给出了此模型具体的求解方法;然后利用Guyan缩减的方法来缩减结构的模态自由度,保证了在进行损伤识别的过程中利用较少的模态参数,进而提高了方法的实用性;最后把所述方法应用于三跨预应力混凝土连续箱梁桥的实际损伤诊断工程。结果表明,利用所述方法进行预应力混凝土连续梁桥的损伤识别是有效的。     

动力作用下盾构隧道接头破坏行为研究

为揭示盾构隧道接头在高速列车动力撞击下的破坏行为,通过建立盾构隧道三维数值模型,对螺栓开裂与否两种工况下的管片接头破坏情况进行分析对比,同时捕捉管片接头与螺栓的动态开裂过程。研究结论:是否引入螺栓开裂对于管片纵向接头的开裂情况有较大影响,引入螺栓开裂后管片纵向接头部位不会出现完全破坏的单元,但其裂缝张开度总体上反而有所增大。撞击荷载下,管片纵向接头率先出现开裂的部位均为弯螺栓处,且环向弯螺栓呈环状断裂破坏,纵向直螺栓纵向剥离破坏。     

H ∞ parameter identification and H 2 feedback control synthesizing for inflight aircraft icing

Aircraft icing accident happens frequently. Researchers try to find new ways to solve this problem. The study is facing the direction of intelligent inspection and control system. Previous studies focused on the principle of aircraft icing and its effects on flight performance. The onboard icing detection equipment can only give the qualitative icing information, but cannot effectively describe how serious the consequences would be. If the icing detection equipment fails, it will cause a serious threat to flight safety. This paper reviews the smart icing system and its fundamental principle. Then based on H∞ theory, an aircraft icing parameter identification method is introduced, and its feasibility is verified by simulation results. Moreover, this method can work normally under noise interference and measurement error. Icing parameter identification method can also test part of aircraft’s stability or control derivatives which would be changed obviously after aircraft icing. Classified by neural networks, the stability or control derivatives’ variation can be mapped to ice parameters’ variation that reflects the severity of aircraft icing. Then H2 state feedback control is designed originally to suppress the impact of noise interference, so aircraft can keep steady after it is iced. Seeing from simulation result of the whole system, it is clear that the system can effectively detect icing parameters and by using feedback control system, it can ensure the safety of aircraft in the flight envelope.     

Intention and willingness to pay for green freight transportation: An empirical examination

The objective of this paper is to explore what motivates consumer intention and willingness to pay for green transportation. The model is based on the theory of planned behavior and explains the relationship between consumer attitude, perceived behavioral control and peer pressure on intention and willingness to pay for a t-shirt that was transported using energy efficient fuel. Data from a survey of U.S. consumers is analyzed. Results suggest consumer attitude and peer pressure are positively associated with intention which is positively associated with willingness to pay. High levels of consumer attitude, perceived behavioral control and intention suggest a positive outlook for organizations investing in green transportation initiatives. Results also suggest a need for organizations and government to market and educate consumers and citizens about the positive implications of green transportation and using energy efficient fuel.     

铁路超细粉煤灰预应力混凝土梁疲劳性能试验

通过9组32m铁路预应力混凝土标准梁的缩尺模型,对掺用超细粉煤灰的预应力混凝土梁在重复荷载作用下的力学性能进行研究,探讨粉煤灰掺量,混凝土等级以及养护条件等因素对铁路桥梁粉煤灰预应力混凝土梁力学性能的影响.试验结果表明:经200万次重复加载后,模型梁静力及动力特性与加载前相比基本不变,超细粉煤灰的合理掺用对梁体疲劳性能没有不利影响,为铁路桥梁粉煤灰预应力混凝土设计参数的选取及应用提供技术支持.     

半刚性基层沥青路面横向裂缝的演变规律

为了研究沥青路面横向裂缝的演变规律,依托江苏省高速公路历年的检测数据,选取部分路段进行精细化跟踪观测,考虑了环境和材料等因素的影响,分析了横向裂缝密度随路龄的演变规律,建立了演变模型,进行了预测分析。结果表明,横向裂缝受低温的影响较大;与AK-13或PAC-13相比,上面层材料采用SMA-13时裂缝密度较小;横向裂缝的宏观演变规律呈现出初步发展、稳步发展、快速发展的三阶段特征,可以使用结构行为方程表征;当路面养护及时时,裂缝发展较慢,方程参数β值较小。     

机场刚性道面地基参数识别研究

提出一种机场刚性道面无损检测中的地基反应模量K的动态识别方法，以运动荷载作用下的粘弹性Winkler地基上的板系统的动态力学计算模型的方程解析解为基础，应用最小二乘方准则来拟合实测动挠度和理论动挠度，从而识别出地基反应模量K。通过实例计算，表明识别结果可靠。     

加筋挡墙加筋机理及其力学行为的分析

随着加筋挡土结构在我国公路建设中被广泛研究和应用,加筋挡墙的加筋机理及其力学响应分析越来越引起重视。在研究加筋挡墙的加筋机理及复合土体强度特性的基础上,运用AN SY S分析软件对加筋挡墙的受力机制及力学行为特点进行模拟计算分析,得出了一些有益的结论,对加筋挡土工程具有指导和借鉴作用。     

Travel to work and household responsibility: new evidence

A persistent empirical finding in the research on travel patterns is that women tend to engage in shorter work commutes than men. Research evaluating the degree to which this gender differential in commuting may be explained by the division of labor in the household has produced decidedly mixed findings. This paper presents a critical review of the methods and results of recent research on the gender differential in commuting along with the associated implications for the household responsibility hypothesis (HRH). While all of the articles reviewed are informative and unique, not all conclusions are well supported. The paper then tests the HRH using the 1990 NPTS travel data. The new evidence confirms that women continue to exhibit shorter commute times and distances than men and provides support for the HRH. The paper concludes with a summary of findings and recommendations for further research.     

A study of the bi-directional pedestrian flow characteristics at Hong Kong signalized crosswalk facilities

This paper investigates the bi-directional flow characteristics at signalized crosswalk facilities in Hong Kong. Pedestrian flow measurements were conducted at selected signalized crosswalks in Hong Kong urban area with and without the Light Rail Transit (LRT) railway tracks in the median of the carriageway. The pedestrian speed-flow functions for these crosswalk facilities were calibrated. The relationships between the walking speed at capacity and directional distribution of pedestrian flow (or flow ratio) are determined. The effects of different flow ratio on the effective capacity are also investigated. The bi-directional pedestrian flow effects on signalized crosswalk facilities with LRT tracks are found more significant than those without LRT tracks. The result could be used as a basis to improve the assessment of the crosswalk's capacity and to determine the design walking speeds under different flow ratios at signalized crosswalks in Hong Kong and in other Asian cities with similar environments.