JOURNAL OF TRANSPORTATION RESEARCH
Year:2006 | Volume:3 | Issue:3|Papers Count:9

Due to their high rate of construction and economical advantages, roller compacted concrete pavements (RCCP), are finding increased use in many countries. RCCP has successfully been used for pavement construction in ports, cargo terminals, low speed roads, parking lots and heavy and military vehicle roads. Research and development is continuing to improve skid resistance of this type of pavements which should lead to its wide spread use in high speed roads.Due to their large surface area, concrete pavements are sensitive to the curing method and duration which is applied for them applied. Roller compacted concrete pavements (RCCP) are expected to be particularly sensitive in this regard due to their low mix water content. It is thus important to characterize the effect of various curing regimes on strength and durability of RCCP concretes, so that appropriate minimum curing requirements can be set in project specifications.In this research, effects of three different curing regimes, namely; water curing, application of curing compounds and air curing, on strength and permeability of RCCP mixes were investigated. The experimental work was conducted on two different RCCP mixes with 275 and 350 kg/m3, of cementations materials. The results of experimental program showed the substantial effect of curing regime on strength and durability of RCCP mixes. Considering water curing as the reference, curing in laboratory environment with a relative humidity of 40%, resulted a 45% reduction in compressive strength. Similar reduction was observed for bending strength. Curing by chemical compounds was not very effective in improving the situation and 35% reduction in both compressive and tensile strength was observed, compared to wet curing regime. The effect of curing on durability characteristics, such as water absorption and coefficient of water permeability followed a similar trend to that observed for strength, but was even more severe. Silica fume is considered as an effective industrial additive that is widely used when concrete with high strength or durability is required. The effect of incorporation of silica fume at a replacement level of 10 percent of cementations materials on properties of RCCP mixes and the sensitivity of such mixes to various curing regimes was also investigated. The results showed that incorporation of silica fume at the aforementioned dosage resulted an increased water demand of about 10% percent in order to keep the same level of workability as the control mix. Due to the increased water demand and water to cementations materials ratio, the incorporation of silica fume resulted in only a modest increase of strength characteristics of 5 to 14 percent. Improvement in water absorption and permeability characteristics of RCCP due to incorporation of silica fume was also modest for the same reason.  

In this paper train conductor scheduling in railway network is discussed according to the periodic need of railway to these schedules as a result of periodic train scheduling. By network representation that is consisted of nodes and arcs, a graph is set up by a set of stations and rail links. This graph shows complexity of the discussed railway network. The arcs of the graph represent roundtrips, thus by establishing the roundtrips all the working trips between the stations (nodes) are covered.Roundtrips are generated by heuristic algorithms, for example heuristic algorithm of branching. This algorithm specifies definable roundtrips all over the railway network. Outputs of this algorithm are characteristics of existing roundtrips in each depot, starting and finishing time of each roundtrip as well as covered routes. Afterwards the characteristics of roundtrips are used by roster generation algorithms and clique generation. Clique is used for roundtrips that have overlap with each other and thus can not be performed by one single group of crews. Roster generation is used for evenly generating time shift tables. The rosters used, divide workloads evenly among different units of time. Workload of each roundtrip, duration of the roundtrips, etc.. In this way the roundtrips are assigned so that workload of each unit of time is similar to others.For assigning similar work load to different periods of time, an f(z) can be used as an objective function that controls the quality of rosters. But as this objective function is non-linear and NP-hard, instead of an exact approach, a heuristic algorithm is used that generates one periodic roster for each depot. This algorithm generates rosters as dense as possible so that it can achieve some levels of optimality. Finally by roster generation algorithm rosters are turned into work shift schedules. In this stage it is important that all the roundtrips assigned to one unit of time in work shift schedules are performed by one group of crews at that unit of time. For showing how the algorithms are used and that better results have been achieved comparing to the current procedures of crew scheduling in Iranian railways, some real examples are included. The achievements in comparison with current situation are: Reducing travel time by generating optimum roundtrips for crews Reducing the number of crews for covering defined roundtrips in each depot. By roster algorithm, the working standards are considerably taken into account. The long paths by which the working time period of the service crew is more than the standard level, reaches to half. The nightly resting time is cancelled except for home depots, and as a result, the dormitory costs are cut. Priorities of this method which divides the railway network to different depots in phase 2 is that the assignments allocated to each depot will not be too large. It means that the number of missions becomes very smaller compared to the dimensions of the network and this, specifically causes reduction of solving time by the computer software.

In this research the variation of Marshal stability with percentage of crushed aggregates is simulated using Artificial Neural Networks (ANNs) with Levenberg-Marquardt Back Propagation (LMBP) training algorithm. To develop the model, the percentage of crushed aggregates, percentage passing through sieves 50, 20, 4, 8, 30 and 1/2 inch and percentage of asphalt content considered as network inputs and Marshal stability as network output so the number of input layer neurons is eight and the output layer neuron is one. The tangent sigmoid transfer function is selected for hidden layer neurons and linear transfer function for output layer. The inputs and outputs are normalized between -1 and 1, to improve the performance of the networks. At the first stage, the maximum generalization ability of each network with specified number of neurons (3, 5, 8, and 10) in hidden layer is determined. Comparing these maximum values reveals that the network with 8 neurons in the hidden layer has the maximum generalization ability. At the second stage, the variation of Marshal stability with percentage of crushed aggregates is simulated by applying sensitivity analysis on the network with maximum generalization ability. MATLAB 7 has been used as main software in this research. In order to collect the required data needed to design networks and evaluate the generalization ability of them, a database of 110 Asphalt concrete specimens are selected before compaction from the road surface. The specimens include Binder and Topeka with 0-19 mm gradation. The Binder Type is asphalt cement with the penetration grade 60170. Having done the Marshal stability, extraction, percentage of crushed aggregate tests, the Marshal stability, the asphalt content, the gradation curve, the percent of crushed aggregates are derived. The optimum number of hidden layer neurons is determined based on 85 data for training and 25 data to assess the generalization ability of the networks.

There are many methods developed for measuring the qualitative and quantitative parameters of traffic, but few research works have been done for measuring the position of vehicles. In these research works such as the one presented here, position of every vehicle is determined and according to the application, other traffic parameters can be calculated using the position of vehicles.For studying the microscopic movement behavior of vehicles in the basic freeway section, it is important to determine the position of vehicles in every time step. In this research a system has been developed which determines the position of vehicles in the considered section of freeway using simple image processing algorithms. Simplicity of the algorithms has reduced the execution time of the prepared image processing software and accuracy of the positions of vehicles is about the dimension of a private car, this accuracy is enough for most of the microscopic traffic studies. Input of the developed system is a video film of the vehicle movements and the output is a table of vehicles positions in the freeway. Using the table of vehicles positions in the freeway, trajectory of vehicles can be determined.Trajectory of vehicles can be used for modeling the drivers' behavior. Drivers' behavior models can be used for micro simulating of traffic. In addition, macroscopic traffic parameters including, number of passing vehicles, average speed, and other traffic characteristics can be calculated. Using image-processing techniques instead of manual methods increase the accuracy of measurements and a tedious work for human can be done by machine. Therefore, larger statistical samples can be collected. In addition, obtained data can be relied on and expenses are cut down. Regarding the fact that lack of safe distance observance is one of the main reasons of collisions, calculation of longitudinal distances between vehicles is introduced as an application of the developed system.In many images taken from the streets, in addition to the considered vehicles, there are other vehicles and pedestrians moving near the considered street. Thus, it becomes important to distinguish between the considered vehicles and other moving objects in the taken images. In this research, the considered street has been divided into windows and subsequently is used for image processing. The size of these windows is determined as if they can produce a complete view of the considered street with enough resolution and accuracy.In the developed system, position of vehicles can be determined without needing special devices.In addition, without knowing pan, tilt, focus, and height of the camera, only with knowing the co-ordinate of 4 points of the image in the real world, distances and positions in the street can be calculated. The basis of the developed image processing system is a projective model that a point on the street can be related to a respective point on the screen. Thus, all points on the street plane, which can be seen in the camera picture, are known. Windows are arranged in horizontal rows. Each row contains a number of windows. Considering the nonlinear projection of 3D images to 2D images, vertical distances between rows of windows are determined by a nonlinear equation. The distribution of the windows is determined as if all of the distances between rows of the windows show a specified distance, e.g. 1 meter, in the street. In this way each window would be matched to a specified space on the street. Each window is processed for detecting whether there is a vehicle in it or not. In the developed computer program, an effective algorithm has been used to detect the vehicles in individual windows. In this algorithm, averaging the pixels of that window in the sequence of all images, produces background of that window, and then moving vehicles can be detected by differentiating each image from its background. In the differed picture, pixels, which h.ave high values, suggest presence of moving object, which in this case is a vehicle. When the number of pixels related to a vehicle exceeds a threshold, that window is considered to detect a vehicle. Such a process is done for all the windows in the images. In this way, all vehicles can be detected in the specified sector of the street and subsequently the position of vehicles can be determined and calculated in every image. If a vehicle can be seen through any of these windows, the corresponding value of that window will become 1, otherwise it will become 0. In heavy traffic when the images of vehicles conflicts and frontier edge of vehicles cannot be seen this system looses its efficiency.

Gravity structures are used for waterfront quay walls where the seabed soil condition is appropriate. Some gravity walls are built behind a cofferdam on land but most walls are constructed in water by a method used only in maritime works, in which large pre-cast units are lifted or floated into position and installed on a prepared bed under the water. It is usual to use rubble or a free-draining granular fill immediately behind a quay wall so that the effects of tidal lag are minimized and earth pressure is reduced.Gravity quay walls can be classified into different types such as caissons, L-shaped blocks, rectangular concrete blocks, cellular concrete blocks and cast in-place concrete. Optimum design of block work gravity type quay walls with pre-cast concrete blocks are the object of the present investigation. The advantages of these quay walls are: simple construction technology, preferred costs and good durability.The external and environmental loads acting on these type structures are surcharge, deadweight of the wall, earth pressure, residual water pressure, buoyancy, seismic forces, dynamic water pressure during an earthquake and tractive forces of vessels. The principle modes of failure of this gravity structure are: sliding, overturning, deep slip and foundation failure, therefore in the stability calculations the following items should be examined in general: Settlement, Circular slip, Bearing capacity of the foundation, sliding and overturning at all horizontal surfaces between blocks. To study the behavior of a quay wall and to check the stability against probable different failure modes, a computer program has been developed. This program can easily consider the effects of different parameters such as section geometry of quay wall, material property and loading condition in design.In common designs, designers often select an accepted sketch with their experiences and cannot review different sketches and present the best one. Sometimes the final drawing may be uneconomical and also the transport and placing of blocks may be very difficult and probably impossible. Therefore, adopting an optimization procedure for design of these structures is needed. In this paper, a procedure for optimization of cross section of a block work gravity type quay wall has been introduced and a numerical program for this procedure has been developed.After reviewing design and construction considerations for such quay walls, available methods for optimum design of these structures are discussed and objective function, constraints, design variables are considered. The main constraints of the optimization problem in the present study are the safety factor in various modes of failures. As relation of safety factor with design variables is unknown, therefore, a proper method should be used for approximating the objective function and constrains according to design variables first: Then, an efficient method should be selected for formulation of mathematical optimization of the objective function under existing constrains.For this purpose, the optimization of the cross section is accomplished using Sequential Quadratic Programming (SQP) method in the present work.Results indicate that the cross section of a block work quay wall has an important role on stability of the structure and one can reduce costs of such structures by optimizing the cross section. Finally, some recommendations for optimum design of this type of quay wall are presented.

Flexural toppling failure occurs due to tensile stress caused by in-situ rock column moments.Observations and theoretical analyses carried out by researchers show that the total failure plane is perpendicular to the rock mass discontinuity plane. In this paper, to analyze the flexural toppling failure, each rock column is modeled as a cantilever beam. Then using the laws of the strength of materials, along with the limit of equilibrium, the safety factor is found. Although the result of this analysis is comparable with those of laboratory tests, their use in real slopes shows a safety factor more than what it has to be. This is due to stress concentration around and near the tips of structural defects in the rock mass. Calculation of the amount of stress concentration around structural defects, based on the laws of the strength of materials, is cumbersome and has not been observed in the analysis of flexural toppling failure. In this paper, for the first time, structural defects of in-situ rock columns, with a potential of flexural toppling failure, enter the analysis. In nature, structural defects in rock masses appear haphazardly and unevenly in different locations. However, due to brittleness of the rocks, the rock defects generally appear in the form of ended cracks. Keeping this in mind, to analyze rock columns with structural defects, we considered a single ended crack perpendicular to the column length resulting total failure.Hence, in this case, based on the theory of fracture mechanics, each rock column, with respect to the length of the crack, acts like a beam with two infinite ends.  

Geometric conditions of road and railroad in their cross- points has fundamental role in increasing or reducing the number of accidents occurring between rolling stocks and road vehicles. In addition, traffic intensity, rail route system, type of crossing road vehicle, type of road super structure (asphalt, sandy and ground), crossing signaling system and sight distance (which is dependent to the crossing geometrical situation) are other parameters affecting the number and severity of the accidents. Considering the above mentioned points, the primary step to make the level crossings safety is prioritization and categorization of the crossings in higher, intermediate and low risky groups. In this paper, hazard index has been primarily defined considering the situation level crossings in Iran, by using experiences of some developed countries and then the existing level crossings in rail-road transportation network has been studied. In spite of increased number of rails as well as road vehicles, irregular development of the cities etc, it is predicted that up to the end of the Fourth Social, Economic and Cultural Development Plan of the Country, accident rate in level-crossings will be reduced to 20%, by fulfillment of the mentioned plan in Iran, and also it will be reduced from 44 average per year in the Third Plan to 30 accidents during the Fourth Plan.Statistical data analysis also showed some other results as follows:1- The level crossing accidents according to train - Km have had a descending trend,2- Specifying priorities of crossings according to the risk index has had more desirable and more realistic results3- The low cost safety measures have been considered in the short term plans and it is assumed that until the end of 2009, a 20% reduction will be witnessed in the crossings accidents compared to that of the Third National Development Plan.