JOURNAL OF TRANSPORTATION RESEARCH
Year:2010 | Volume:7 | Issue:2 (23)|Papers Count:8

Mechanical and physical properties of aggregates are among those parameters that determine their application as pavement surface layer. By now, there are standard procedures, mostly experimental, for evaluation of aggregates. These tests describe geometric condition, strength and durability of aggregates. There are also some mechanical field tests for quality control of aggregates. Studies demonstrate that meaningful relationships exist between physical and mechanical properties of aggregates. However, in much of the studies, these relations are not clearly specified. In addition, results are to some extent scattered due to diversity of aggregate categories.In this paper, to know the exact relationship between aggregate properties and their correlation to each other, carbonates, sandstones and igneous specimens were selected from different mines. Some physical and mechanical tests including specific gravity, impact value, Los Angeles abrasion test, weight loss due to sodium sulfate and polished stone value were carried out on specimens. Data analysis of results showed that impact value and Los Angeles abrasion values have meaningful linear relation. This relation is stronger in igneous rocks and sandstones in comparison with other categories. Based on various evaluations on PSV relation with other physical and mechanical parameters, it has been clarified that there exists a linear relationship between PSV and specific gravity leadind to reduction of PSV. In a broader range, a linear relationship is observed between PSV and a combination of specific gravity and sodium sulfate weight loss.

In recent years the recycling of concrete to produce aggregates suitable for non-structural applications, such as road construction materials, is emerging as an environmentally viable and technically feasible operation. While studies on the engineering properties of concrete made by recycled concrete aggregate abound only limited data are available on performance of crushed brick aggregate in road construction. This paper is an attempt to understand the physical properties of recycled masonry bricks and cement mortar or concrete made of natural aggregate. The study also provides the laboratory basic test results required to assess the mechanical performance of the unbound aggregates for use in road construction. In the present research study, the possibility of demolition debris recycling and its utilization in base and sub-base layers of roads, directly or after improvement, is investigated. A vast variety of physical and chemical tests has been carried on crushed bricks, mortar cement, concrete or different combinations of these materials. Freezing and thawing, durability, compaction and CBR tests are the most important tests to be executed for evaluation of the performance of these materials for use in construction of road layers. The initial test results indicate that these materials may be considered as sub-base materials for second degree (immediate traffic) roads. To enhance the quality of the recycled materials, two methods were employed. In the first method, different fractions of recycled construction debris were replaced with high performance materials. This led to an increase in CBR amount, i.e. increasing the new material performance. At the second method, cement with different percentages was added to the recycled materials including brick and cement mortar. Again, this resulted an increase in compressive strength of new materials. Also complementary experiments indicated increased quality of construction debris as base course material in highway construction.

In practice, the railway track has infinite length. Boundary conditions of these structures are quite complicated. Therefore their modeling is usually carried out by accepting some assumptions for boundary conditions. There are various methods of modeling by forming equations of motions and dynamic analysis. One of these methods is modeling the railway track by finite element method. Generally in such modeling, a limited length of a track is modeled and executed by implementing some boundary conditions. Assortment of boundary conditions has an effect on dynamic responses. To reduce such effects, the length of the track is usually chosen to such a measure to minimize the dynamic responses of the end points of the track elements to zero. Doing so would cause an increase in the length of the track and hence adds to equation's degrees of freedom, as well as volume of output and prolongation of analysis time. For this reason, a combination of finite elements and infinite beam elements (two end elements) has been proposed for railway track modeling.Also, matrices of mass, damping and stiffness of an infinite element which has been laid on a visco-elastic bed, have been calculated by implementing selected shape functions. Therefore, by applying two infinite beam elements on either side of the model, a railway track is formed like a beam on an elastic bed which creates the possibility of eliminating the boundary condition effects.

In Iran railway network, prestressed concrete sleepers are more popular than other types, due to their more resistance and other advantages. One of the defects observed in this type of sleepers, is longitudinal cracking, before and during operations that usually start from roll plaque and continues to the middle of the sleepers. These cracks may be formed due to excess pressure within the roll plaque of sleepers, water freezing inside roll plaque, existence of fine aggregates when closing the bolt of roll plaque, distortion and lack of standard bolt or roll plaque or other destructive factors. In this paper, approximation and modeling of the effects of mentioned factors by cylindrical pressure in place of roll plaque holes are presented. Numerical studies with minimal changes in geometry of monoblock prestressed concrete sleepers B70 and by the hole of location and roll plaque reinforcement modeling were done and the relation between unwanted additional stresses inside the roll plaque with concrete were investigated. By cylindrical pressure in place of roll plaque and increasing it to concrete failure, impact of this pressure in place of roll plaque is presented analytically and experimentally. The results show that unwanted stress in place of roll plaque increases the cross tension stress, due to cracking. In the next step, by considering the path and distribution of cracks and strengthening transverse reinforcements, transverse tension stress in various patterns of strengthened and non-strengthened sleepers, is investigated. The results show that use of transverse reinforcement can control cracks and reduce the tension stress around holes of the roll plaque.

In this study, factors influencing driver and occupant injury severity in two lane , two way roads of Iran are identified. Using statistical models is one of the most common methods that were employed to analyze crash severity. In this study, in addition to examining such models and expressing their weak points, CART method is introduced. Classification and regression trees (CART), which is one of the most common methods of data mining, was employed to analyze the traffic crash data over a three-year period (2006-2008). Expressing models in decision tree format with explicit rules is one of their most useful outputs. In the analysis procedure, the problem of three-class prediction was decomposed into a set of binary prediction models and then eight models were analyzed. This resulted higher overall accuracy of predicting the model, besides the prediction accuracy of the fatality class, which was nearly 0%, and in most of the previous studies, increased significantly. Results indicated that improper overtaking and ignoring seat belts are the most important factors affecting the severity of injuries.

Directional midblock median openings with Left-Turn Lanes and Loons between four-leg signalized intersections without median openings are designed to smooth flow of traffic especially on main streets. In recent years, there has been growing interest in their potential benefits as raising mental capacity of drivers by increasing the flow and reducing the delay caused by traffic signals. This interest has developed a need for data on safety effect of U-Turns. In this paper, the safety effect on u-turns crashes of converting signalized intersections in Tehran from traffic signal removal to install directional midblock median was estimated. The six such conversions were studied in this research. Safety analysis of u-turns conversions was done by modeling of U-turns crashes by statistical methods. Accident prediction models for crash types and crash frequency were developed to examine the geometry and traffic factors contributed to the crashes at u-turns conversions. The data analysis results show that a 10% increase in separation distance (weaving length), external radius and median opening length will result in a 2.36%, 37.6% and 12.6% decrease in angle crashes, respectively. Also, a 10% increase in roadway width will result in a 20% decrease in total crashes. Increasing speed on major roadway, will result increase in rear-end accidents due to large speed differential between u-turn and through vehicles. Therefore speed increase on minor roadways that converges to the major ones, will result in decrease in rear-end crashes. Furthermore, total crashes and crash types are increased with the ADT increase on the major streets and u-turns.

The Railroad Blocking problem is one of the most important problems in freight railroad areas. Solving the Railroad Blocking problem reduces the operational cost of railroads considerably and saves time in moving the freight as well. However, Railroad Blocking problem in medium and large size is not solved by any of the commercial software available in the market. This research presents an algorithm based on Simulated Annealing Algorithm for solving the railroad blocking algorithm that is able to solve the problem in a reasonable CPU time. To analyze the efficiency of the algorithm and check for the quality of solutions, experimental analyses are conducted. Two sets of small and large sized problems that were generated randomly are solved. Results on the set of problems are compared to those of solutions generated via CPLEX, one of the well-known solvers for solving both linear and mix integer programming problems.