فصلنامه مهندسی حمل و نقل
پیاپی 2 (زمستان 1388)

Comprehensive Analysis of masonry structures (e.g, arch bridges as historical monuments) makes important challenges for design engineers, thanks to complexities of behavioral patterns of discontinuities as well traditional construction techniques. Main portion of deformations in masonry units is due to probable movements between masonry blocks. Discrete Element Method (DEM), based on explicit presentation of blocks and joints, is a powerful numerical tool which is able to consider more details on architectural elements of masonry structures. In this research, using 3DEC program, application of DEM in analysis of masonry discontinuous domains is studied. To verify the program, the behavior of some simple structural systems as well as that of some real structures is studied and then, main model of arch bridge is analyzed. In this research, using numerical studies of seismic behavior of masonry arch bridges, time-histories of structure response are obtained to be used in simulation of failure process of structure. Post tensioning method, as one of the common methods in rehabilitation of slopes and tunnels, is proposed for seismic rehabilitation of masonry arch bridges. The results of this research show the suitability of the proposed method for seismic rehabilitation of masonry arch bridges.

The Economic Cooperation Organization (ECO) region has a good potential for freight transit due to its geographical location. The region can act as a land bridge between Asia and Europe as well as having a vital role for the development of Central Asia land-locked countries. To promote the trade and transit among these countries, appropriate transportation infrastructure and services are required. Logistics is the management of the flow of goods, information and other resources, including energy and people, between the point of origin and the point of consumption in order to meet the requirements of consumers. Logistics involves the integration of information, transportation, inventory, warehousing, material-handling, and packaging, and occasionally security. Logistics is a channel of the supply chain which adds the value of time and place utility. Logistics parks are the key element of good intermodal transit transportation. The core of the strategy to develop logistics parks is industry capacity development with a focus on assisting logistics service providers to build their own enterprise capacity. Logistics parks help governments to promote the development of modern facilities in a new industrial cluster – including a major truck-park, transportation terminals, distribution centers, processing facilities, a logistics incubator, and a technology center. In this research, an optimum location-allocation model for development of logistics parks in the ECO region to provide services for transit freight is presented. Transport and logistics requirements are determined based on an assessment of the agricultural and resource sectors, and the light and heavy industries associated with those sectors. Special attention should be given to the role as a “transit-hub”. Based on our scope to provide services just for transit freight, the role as a transit hub is considered as the demand of logistics parks. There are no logistics parks in the ECO region. Also service providers as well as local transport operators, terminal facilities and distribution centers that all play roles in the logistics industry are in poor condition. In fact logistics industry (supply) in the ECO region is weak. Freight demand and supply are taken into consideration to determine the location of logistics parks. Based on demand role as transit hub and weakness in the supply sector, transit hubs are considered as the best location of logistics parks.

Transportation management on both the supply and demand sides, due to ever increasing traffic problems is nowadays, considered as a crucial issue by transportation planners and engineers even in developing countries. Ramp metering as a transportation supply management measure with noticeable improvements in performance of the existing infrastructure and more effective use of the limited resources with comparatively little cost, is the focus of this paper. A mathematical programming model is designed to optimize the traffic volume on highways and their ramps via controlling the entrance volume of vehicles through different on-ramps, as decision variables. Flow conservation constraints are the major constraints in this model. A section of Sadr Highway is analyzed as the case for empirical study, for which traffic surveys including traffic counts is administered for the whole section under study. Results show that the flow of vehicles in the selected highway section can increase up to about 6 percent. The adversely high effect of Shariati on-ramp on the whole system under study indicates that its traffic flow can be reduced to 13 percent, with still positive effect on the whole system. Modarres on-ramp is the only ramp that is acting below its boundary limit and needs not any metering in the current circumstances.

Rail bed modulus is one of the main parameters in optimal track design which is determined based on components of ballasted railway tracks. Perception of track bed behavior in different conditionsand on substructure with complex characteristic has an important role in the rail system analyses. Technical and geometric characteristics of track may have a significant impact on rail bed modulus. Review of recent researches on railways in different countries indicates the importance of rail supporting system in rail analysis results. This paper studies the importance of change in rail bed components characteristics in determining track modulus as one of the parameters of rail system analysis and design. This study is divided into two parts including field tests and numerical analysis. To achieve this goal, ballasted railway tracks are modeled according to technical and geometrical characteristics. Then, model is calibrated using field test in order to confirm the validity of model, and it is analyzed by employing finite element method based on tracks components classification. Finally, some diagrams and tables are presented for different conditions of rail roads according to ballast layer thickness and the type of the subgrade in order to determine track modulus and control rail vertical deflection.

One of the major concerns regarding to the urban and intercity railways operation is ground born vibration. This phenomenon not only causes damages in railway substructures but leads to annoyance for people who live in track neighborhoods. Railway embankment including natural fills in addition to providing a suitable foundation for track could be considered as a potential solution to minimize these effects. Reviewing the analytical models to evaluate the railway vibrations, it could be understand that the effects of railway components especially the embankment on vibration reduction have not been investigated clearly. In the current study, through development of a new analytical model considering the railway dynamic load, in addition to study the effects of railway components on track vibration; the embankment effect in vibration reduction has been especially investigated. For this purpose the dominant differential equations on track dynamic behavior have been derived by replacing track components as a series of mass, spring and dampers under the railway sinusoidal load. Consequently, the governed equations have been solved numerically using a MATLAB code. In order to investigate the role of embankment in comparison to the other components, during the track dynamic analysis a series of parametric study have been accomplished on train axle load and speed as well as thickness, stiffness and damping of embankment. The numerical results show the remarkable capability of embankment material on vibration attenuation. As an important finding it has concluded that the embankment thickness up to 3 meter have a predominant effect on vibration reduction.

In order to analyze the frost temperatures of the central Zagros in the Lorestan and Chaharmahal regions, the daily minimum temperatures of 14 weather stations were obtained from the Meteorological Organization of Iran. The mean dates of the beginning, ending, and length of the frost period were calculated for each station. The frequency and duration of different frost periods (1, 2 and over 7 days) were calculated. The results showed that the frost period begins in the northern and mountainous parts of the study area earlier than the southern parts and the lowlands. The length of the frost period showed the same behavior. Although the frost period begins at the same time in both the north of Lorestan and the east of Chaharmahal, but the mountainous nature of the eastern Chaharmahal postponed the end of the frost period. The frost period frequencies with different intensities were higher in the mountainous parts. Especially the frequency of days with zero to -10 degrees Celsius was remarkable. The variability of the beginning date was much higher the variability of the ending date, especially in the mountainous areas. Findings of the study demonstrate the necessity of the installation of road weather stations and weather watching instruments in the mountainous parts of the study area.

Reduction in incident response time is one of the incident management programs. As a component of incident management system, Freeway Service Patrols (FSPs) have a key role to response incidents better through reducing the time of detection, verification and responding. This paper is to propose a fleet allocation model among patrol routes to minimize incidents response time. We attempt to minimize the response time of patrolling trucks to incidents, for all of incidents that occur in a certain time period, by a nonlinear programming model. This response time for FSP is divided into two sections, the first is the time of traveling with predefined speed in the free flow traffic conditions and other is the time it consumes on the incident queue. Finally, the proposed model has been implemented in Tehran freeways to show the practical capabilities of it. The results show that optimal fleet allocation by this model can reduce incident response duration and mitigate non-recurrent congestion due to these events, compare with other traditional fleet allocation methods.