پژوهشنامه حمل و نقل
سال دوم شماره 2 (پیاپی 3، تابستان1384)

Bridges are utilized as vital arteries for urban and intercity transportation systems. In our country, Iran, there are several bridges, that seem weak against the existing live loads. These bridges are resistant from static point of view, but their partial and overall seismic performance should be interrogated and after determination of vulnerable points, a suitable retrofitting scheme should be presented.The purpose of the present study is to carry out the above-mentioned task for a specific model of existing bridges. The studied case is an orthotropic steel bridge. At first, seismic vulnerabilities of steel bridge during past earthquakes and recommended appropriate methods of retrofitting were studied.In order to render a performance assessment of the bridge, a nonlinear pushover analysis was done. The nonlinear response of the bridge was investigated from the first pier hinging to the inelastic equilibrium condition during the design level earthquake (DLE) and then to the ultimate limit state(ULS). During the yielding process and reduction of the bridge structure’s stiffness, its influence on the period lengthening and effective viscous damping was specified.

In this paper a techno – economic model for selection of intercity high speed rail transportation based on the specific characteristics of the country is presented. Costs and benefits of high speed railway system has been estimated on the actual data. To estimate the passenger traffic volume of the route as the main variable to evaluate direct benefit. The Analytical Hierarchical Process was applied. To estimate the indirect benefits some variables such as the value of time, energy saving and level of service are taken into account. Costs and benefits of the system were compared based on the Net Present Value Method. To evaluate the proposed model, the Tehran – Isfahan high speed railing which is at the early stage of construction was selected as the case study.

Experimental studies show that an indeterminate structure or a concrete continuous beam does not fail when critical sections reach their ultimate strengths. In other words, if a structure has adequate ductility, moment and stress redistribution will take place in the members by developing the plastic hinges at critical sections, while the other sections of the member achieve their ultimate strengths and capacities. Iranian concrete code allows for moment redistribution in terms of steel ratio of the beam section and limits it to 20 percent in critical regions. However ACI 318-02 defines the allowable moment redistribution in terms of net tensile strain in extreme tension steel () and limits it to 1000 percent, but not more than 20%.In the current study, the limitations of moment redistribution defined by Iranian concrete code, is discussed and a comparison is performed with ACI 318-02. To do so, governing equation of allowable moment redistribution is extracted, with regard to the required ductility in continuous beams. Afterwards, the effects of some different parameters, for instance, the magnitude of support elastic moment, the ratio of length to effective depth of continuous beam, and the strength of steel reinforcement, on the amount of moment redistribution are investigated and the results are compared with the limitations of ACI 318-02 and the Iranian concrete code. It is shown that the moment redistribution in reinforced concrete continuous beams based on the regulations of Iranian concrete code is not in a safe margin in some cases.

Granular media are non continuous media that their structure is made of in touch granules with different shapes and sizes. The materials used in unstabilized subgrade and pavement layers are such media. Study about the behavior of granular materials at the loading time needs to analyze variants in two microscopic (local) and macroscopic (global) levels. The behavior of granular materials is influenced by their geometrical structure as well as micromechanical variants. Nowadays numerical simulation is one of the methods which is used for studying the granular media. In this paper by numerical simulation of biaxial pressure besides of showing of variation of geometrical and mechanical of environment during loading it will compare the result of numerical and experimental simulation.

Road accidents are the consequence of combined effect of behavioral, technological and environmental factors. In this paper, the spatial dimension of weather related road accidents is examined using the data extracted from Police Accident Report Forms. Variations in accident frequency in fine weather, rain, storm, fog and snow were detailed and comparison were made between frequency of accident occurrence and weather condition across Iran provinces. Results show that there is a marked correlation between weather related accidents and the geographical distribution of weather conditions. The results also showed that rain was one of the most important factors in road accidents. Most of the winter season accidents occur during the first frost or snowfall due to lack of the road maintenance services. According to obtained results on visibility data; provinces of Fars and Hormozgan in rain, Chaharmahal and Ardebil in snow fall, Ardebil and Zanjan in fog, Sistan and Baluchestan and Yazd in storm conditions were most vulnerable regions.

Fatigue cracks are amongst the most important factors for destruction of asphalt pavements, caused by excess loads and traffic in roads and airports. Geosynthetics, as strengthening materials, are able to increase fatigue life and prevent early cracks in asphalt pavements, to a large extent. Efficiency of geosynthetics in asphalt pavements depends on many factors including asphalt mix, temperature, location, etc… This paper studies the performance of two types of geosynthetics (Geogrid and Geotextile) on the fatigue life of asphalt blocks with dimensions of 381 x 63 x 50 mm. Samples were provided of non reinforced, reinforced by geotextiles and geogrids, from asphalt slabs for the purpose of testing. Fatigue tests were conducted by four point beam test, and fatigue load by half-sin wave at a frequency of 10 cycle/sec (no rest period) has been used. The end of fatigue life is defined as decrease stiffness to 50% of its primary stiffness. Results indicated that the fatigue life of reinforcement beam with geogrid and geotextile increase 56% and 50% respectively. Furthermore reinforcing layer increases primary stiffness and reduces rate of cracks propagation in reinforcement specimens compared to non- reinforcement specimens.