نشریه فناوری حمل و نقل
پیاپی 15 (پاییز و زمستان 1389)

The objective of all the flexible pavements design methods is that the designed pavement should sustain effective factors. Inter alia, the important effective factors include pavement conditions and states. The designed pavement plays two significant roles in relation with stresses and deformations. Stresses should decrease to such a level that firstly, they are tolerable for the subgrade and secondly, they cause no structural damage in the pavement. In order to actualize this, all the effective ideas should be utilized and effective parameters should be identified and carefully assessed. In this paper, the flexible pavement structure has been modeled using the finite element Abacus software and the effect of tire diameter variations on stresses and strains are studied. This pavement was under a load having circular section and a magnitude of 4.5 ton. Four different diameters were selected for the loading surface and four important parameters having the most effect in coasing defect in the flexible pavements were inspected. Due to the analysis of the models, it was observed that the response of the pavement to each loading surface was different.

According to essence of providing suitable subgrade and embankment for railway tracks, in-situ tests have been attained the considerable importance for controlling the allowable bearing capacity and settlement of the earth works. Usually, earthwork in under construction passenger and freight railways is controlled by means of simple tests such as CBR and Compaction. But in the case of high speed railways, determining the subgrade and embankment layers modulus using Plate Loading Test (PLT) is necessary to ensure adequate bearing capacity and limited embankment settlement. In this regard, the UIC-719R code is stipulated that all the embankment layers including subgrade, bearing part of embankment, sub ballast and ballast must provide a minimum static modulus which is introduced as EV2 (the modulus in second cycle of loading in PLT). Since the experimental process of the PLT is so expensive and time consuming, so controlling the mentioned requirements through the length and width of track, encounters with major difficulties in practice. Recently using the Light Weight Deflectometer test (LWD), the dynamic modulus of the earth works is measured in a very simple and fast manner. As the static modulus has been adopted as a practical criterion for approving the earth works quality in the jobsite, so, a reliable relation between the static and dynamic modulus should be established. The main goal of the present study is to introduce many practical correlation equations between the field tests results including LWD, PLT, and CBR. For this purpose the available data of under construction Qom - Esfahan high speed railway were proceeded in an accurate manner and consequently the best possible correlation equations were presented.

Modal analysis, a recognized subject in civil engineering and mechanics and its applications in other engineering disciplines are developing every day. Modal analysis primarily is used to assess and measure vibrations in structures. It has a diverse applications including detection of damage in structures, monitoring structural health, evaluation of bearing capacity of structures and etc. In this paper, the evolution of empirical modal analysis of evolution and its application in road structures, (especially bridges) are presented. Also, the principal methods of identifying modal input - output and output techniques are introduced. This paper reviewed several reports and experiences of researchers in the laboratory of vibrations and structures’ monitoring in the University of Porto (Portugal).

Accidents are generally considered as multilateral events in which one or more road users can not cope with the conditions and it results to fatal or financial damages. Occurrence of many accidents are predictable. Hence, if the causes and their relations can be identified, the occurrence of many similar accidents can be prevented or the severity of them can be reduced through using appropriate measures. In this paper, previous studies on the causes and contribution of each factor in the formation of accidents are studied, while the contribution of each factor in accidents is estimated. Based on the results of this study, considering the major contribution to the cause of human factors in accidents is not correct and we should consider other factors forming road users mistakes such as road environment, traffic and vehicles and their interaction with the human factor. Apart from the already accepted 90 percent share of human factor in the accidents, it must be admitted that the environmental conditions, road conditions, traffic and vehicle conditions have a significant role in the formation of accidents.

Laser process is one of the most important inventions in the twentieth century. Considering the unique characteristics of this process in comparison with traditional methods, its application in various industries, especially in recent decades, has developed. In order to control the process of hard finishing by laser, identifying affecting parameters is essential. In this paper, these parameters and their effects are studied. Considering the extent of railway industry, hard finishing by laser radiation in various fields can be investigated. In addition to the unique features of this process, such as saving time and energy, precision, reproducibility and etc, the significant annual cost of railway maintenance will be extremely reduced through this process. In this paper, the application hard finishing by laser in railway especially in diesel engines is investigated. Due to the high energy loss in diesel engines, applying this process can decrease fuel consumption and pollution, increase the life of different engine parts and finally decrease maintenance costs. By using this process wear in some parts even can reach to the 1/12 normal status. In addition, through the creation of compressive residual stress, the germination and growth of cracks are prevented the life of parts will be incresed.

Curve lengths are sometimes designed shorter than the required length, while the effect of the length of the curves on the passenger comfort is neglected. In order to study such effect, a thorough literature review was made. Two riding comfort indices are presented (i.e., PCT and NCT). Using a selected data obtained from different resources, a comparative evaluation is conducted to investigate the effect of transition curve lengths on theses indices. The impacts of different transition lengths on change in lateral acceleration, lateral jerk and rolling velocities were also investigated. PCT and NCT were evaluated from the view of seated and standing passenger, followed by conclusions on the importance of the consideration of required curves length in the design of urban railways.

Evaluation of the turning coefficients estimation using dynamic matrix of origin - destination (OD) with macroscopic attitude, for an accurate analysis of traffic light phasing in the framework of an intelligent transportation system (ITS) at three levels is provided. These levels are the process of data collection and classification, data processing, and process of introduction and notification of information by the Kalman filter method (KF). Several intersection in Tehran were examined. Delay time is the main factor describing the function of a scheduled intersection. Delay models are defined based on controlling variables of intersection and traffic flow characteristics. This study sought to provide a delay time model for Tehran intersections with respect to the saturated and under saturated modes, input and uniform random input modes, and conformity with intelligent and non intelligent control systems. Continuous model is analyzing based on HCM-94. The results are related to the continuous model. In this study, delay time is used as an indicator of evaluation.

Empirical 1993AASHTO method is one of the main approaches for design of flexible pavements. But, restrictions of the empirical methods like 1993AASHTO are becoming more and more obvious with improvements in the fields of pavement mechanics and material science. Mechanistic-Empirical Pavement Design Guide (MEPDG) is an attempt to deal with these limitations. MEPDG is a new method recommended under NCHRP Project 1-37A and 1-40D which is based on numerical models. The purpose of this study is to evaluate the design and performance between the empirical AASHTO and the MEPDG method using highest level of data accuracy. Five previously constructed pavement sections designed by empirical AASHTO method have been used in this study. An analysis has been done on the sections using MEPDG and new pavement sections have also been designed and the differences have been demonstrated. The results demonstrate that using MEPDG yields in thinner AC sections, but the amount of reduction is reliant to performance criteria selected. Also it is found that fatigue cracking is controlling criteria for almost all sections.

Due to road users expectations to access to the safe and sustainable roads, and with less demolition and time-consuming corrective activities, the existence of an appropriate approach to optimization of pavement condition and reduction of the costs concerned with the implementation of preventive maintenance program is essential. This approach empowers road agencies to maintain optimal transportation network and to stabilize available budgets. A preventative maintenance strategy considers the importance of preventive repair actions at the earlier time and postpones aging process of asphalt mixtures, which results in a significant decrease in the costs of corrective actions in the future. In fact, preventive maintenance is application of one or more preventive rehabilitation measure on the pavement in order to postpone the expansion of pavement damage. This paper describes the importance of preventive maintenance, the criteria for selection, decision-making tools and most economical maintenance method.