Theoretical method for predicting the weight reduction rate of a box-type car body for rolling stock by material substitution design

In this paper, a theoretical approach is suggested for predicting the structural performances and weight reduction rate of a car body with a box-type section when its material is substituted with a lightweight material for weight saving. For the material substitution design of a car body for rolling stock, bending, axial, and twisting deformations should be considered at constant stiffness and strength conditions. To compare the weight reduction effects on different material applications, some new indices were derived from a structural performance point of view. The derived indices provide good measures to estimate weight reduction by material substitution design and can be effectively applied to the conceptual design of a car body.     

应用回弹恢复评价橡胶沥青的弹性恢复能力

针对橡胶沥青材料本身的特点,分析当前国内外橡胶沥青弹性恢复能力的评价指标,采用常规弹性恢复试验和自制回弹恢复试验仪,分别应用弹性恢复与回弹恢复评价不同种类、不同掺量胶粉橡胶沥青及SBS改性沥青的弹性恢复能力,研究表明回弹恢复更适宜于评价橡胶沥青的弹性恢复能力,可以更好地表征橡胶沥青在较小变形(毫米级)范围内的良好弹性性能.     

连续PC刚构桥下挠变形敏感因素分析

连续PC刚构桥施工过程中受力复杂,变形影响因素众多。文章以在建的罗天乐大桥为例,从收缩徐变、张拉龄期、弹性模量、容重、预应力参数等方面进行参数影响量分析,指出大跨度连续刚构桥线形控制中须重点关注的参数．并介绍了减少跨中下挠的设计与施工方法。     

半刚性基层材料动态模量研究

文章针对我国常用的水泥稳定碎石和二灰稳定碎石两种半刚性材料,通过大量的室内试验研究,建立了两种材料动态模量与无侧限抗压强度和静态模量的关系,为没有条件进行动态模量试验的单位进行路面结构设计提供建议。     

Aggregate expenditure elasticity for transport and communication in Australia

For the purpose of estimating Engel elasticity, one needs to find the best functional form among various alternatives. In this paper, a new function, which is called the double semi-log Engel function turns out to be the best functional form for the transport and communication items in Australia on the basis of the distance function (D²) criterion, and the non-nested hypothesis testing procedure. This function is then used to estimate total expenditure elasticity, and the percentage change in consumer demand due to changes in total expenditure and total expenditure inequalities; using the 1975–76 Household Expenditure Survey data. The results of the analyses demonstrate that transport and communication is a necessary item in Australia on the basis of two criteria, viz., its elasticity is not significantly greater than unity, and the percentage change in demand increases with a decrease of the total expenditure inequality [emphasised by Iyengar (I960)]. Policy implication of the analyses has also been discussed.     

Elasticities for taxicab fares and service availability

This study utilizes a unique dataset from New York City to examine the effects of taxi fare increases on trip demand and the availability of taxi service. The elasticity of trip demand with respect to fares is estimated to be –0.22; the elasticity of service availability with respect to the taxi fare is 0.28; and the elasticity of service availability with respect to total supply of service is near 1.0. These results have important implications for taxi regulatory decisions. First, fare increases do substantially increase industry revenues but at a lesser rate than the percentage increase in the fare. The implication for policy-makers is that fare elasticities must be carefully considered to obtain desired improvements in drivers' earnings. Second, service availability -- an important aspect of service quality that is generally overlooked during fare policy debates -- should be a central consideration in fare setting, given the considerable impact of fares on availability. Finally, where the supply of cabs needs to be expanded, the number of cabs can be significantly increased without harming the revenue stream of existing operators. This finding alleviates a major industry objection to issuing additional taxicab licenses.     

Bridge and tunnel toll elasticities in New York

In 1992, the authors carried out a statistical analysis of Triborough Bridge and Tunnel Authority (TBTA) crossings in New York City, to determine the impact of toll increases on traffic volumes and revenue. Using twelve years of monthly time-series data, we developed a set of multiple regression models that estimated traffic volumes on each TBTA bridge and tunnel as a function of the toll level and other explanatory variables. In most cases, the estimated toll elasticities were negative and much less than 1.0 in absolute value; the median toll elasticity for automobiles was found to be –0.10. Our finding that automobile travel demand is highly inelastic with respect to toll rates is consistent with most previous travel demand studies.     

级配碎石混合料的动力变形特性

采用在古典 C.B.R法的基础上 ,施加动荷载的简化试验方法 ,分析级配碎石混合料的动力变形特性 ,可用永久变形、弹性模量双指标指导混合料的组成设计 ,而合理的级配碎石基层材料组成 ,应考虑到材料与振动碾压工艺的相互作用。     

具有碎石基层的半刚性沥青混凝土路面的非线性有限元分析

在充分考虑碎石基层非线性(弹塑性)特性的基础上,采用非线性有限元法分析了吉林通化试验路3种路面结构面层底面及半刚性基层底面弯拉应力的变化规律,并对通化试验路2种具有碎石基层半刚性沥青混凝土路面结构的沥青混凝土面层的抗疲劳寿命进行了预估。     

加速度计灵敏度校准方法的研究

加速度计已在汽车检测技术中得到广泛应用,加速度计灵敏度校准也愈发重要。通过对传统加速度计灵敏度的标定方法———背靠背方法的分析,提出了一种较为准确的加速度计灵敏度替代校准方法,比较了两种校准方法的优势,并解决了测试系统的安装及数据采集的技巧问题。