مجله مهندسی زیر ساخت های حمل و نقل
سال سوم شماره 4 (پیاپی 12، زمستان 1396)

Intercity high speed trains are amongst the most suitable options for passenger travel. Iran has planned for these transportation systems, especially Tehran-Qom-Isfahan high speed rail project, which is a national megaproject. Therefore, due to the importance of this project in terms of its first experience and travel safety issues, it is discussed in this article. In the present article, by modeling the geometry of rail track embankment and high speed train of this project and simulating the worst weather conditions in the region, based on meteorological data, it is attempted to understand the behavior of high speed train on the proposed track, and to increase the transportation safety factor, the effect of installing of windshield walls is surveyed. Results proved that the presence of windbreak wall reduces the drag force. The outcome of this research can be very effective in raising the safety of travel along the tracks of this high speed rail corridor.

Hot Mix Asphalt (HMA) concrete deterioration due to atmospheric moisture is one of the common problems with flexible pavements. Different tests are used on loose or compacted specimens to evaluate HMA moisture susceptibility. Tests on compacted specimens, such as Indirect Tensile Strength (ITS), are commonly slower and more expensive in comparison to loose mixture tests such as boiling test; but their results are commonly subjective. This paper aims at developing a new stripping index to quantify subjective results of boiling test. Therefore, k-mean classification method was used to identify stripped areas in mixture and a stripping index was developed based on the results. In order to evaluate the accuracy of results of this index, a statistical model was used to find the relationship between the results of this index and the results of ITS. Considering that the model was significant at 95% confidence level and the high value of R2 (0.91), it was concluded that the index is a proper tool for evaluating asphalt concrete moisture susceptibility. In addition, the effects of using Reclaimed Asphalt Pavement (RAP) material and a liquid anti-stripping agent on moisture susceptibility was evaluated. Results showed that application of RAP and anti-stripping agent can significantly decrease moisture susceptibility, such that increasing RAP by 60% and anti-stripping material by 1.5%, the Tensile Strength Ratio (TSR) increased from 71% to 95%.

Bridges are considered as part of the infrastructure of each country, which dedicate themselves a large part of the cost of road construction. Due to their structural elegancy, bridges have high degree of vulnerability to natural disasters such as earthquake, especially bridge columns that carry loads from deck to foundation. So, precise and safe design of bridge components, especially columns, should be considered. The earthquakes which have occurred in the United States, Japan, Taiwan, and Turkey in the 1990s, have caused significant damages to bridges. Bridges require column retrofit due to reasons such as increased loads because of increased traffic, service to vehicles heavier than initial loads, low quality of implementation, seismic issues, environmental issues such as corrosion of reinforcement, pre-stressed losses due to concrete creep and wrapping, change of codes and short column effect in sloping bridges made due to bases with variable height. One of the significant damages in bridge columns depends on shear failure due to the short column effect and inadequate shear capacity of the bridge columns. In this paper, using finite element method, new and combined methods of bridge strengthening with FRP are considered. For this purpose, a short column which was weak in shear, has been modeled and retrofitted by different methods such as wrapping, NSM, and combination methods, and has been analyzed by finite element method. Results showed that the combination method is the best method for retrofitting of short columns bridges.

Engineering structures, during construction and operation, are under the influence of uncertainties including: dimensional parameters, materials specification, and loading. Among engineering structures, concrete structures are more sensitive to these uncertainties with respect to performance problems, environmental conditions and diversity of the components. In this study, the probability performance of roller compacted concrete (RCC), used in pavements, was investigated with different amounts of Lumachelle and pozzolan. The water to cement ratio and the amount of pozzolan and Lumachelle fine aggregates were considered as random variables and also the dimension reduction method (DRM), in combination with Monte Carlo simulation, were used for reliability and sensitivity analysis of this kind of concrete. The experimental design was based on the DRM, and compressive strength and water adsorption tests were performed on the specimens. Results showed that the probability of failure due to water adsorption is 0.17, which is more than the probability failure of compressive strength (0.021) in the RCC. Also, the probability of failure increased to 0.24 by assuming the concrete as a system.

In the last decade, structural waste-recycling and production of recycled concrete- aggregate has widely been considered as an environmental approach. The use of recycled aggregate, produced from recycling of demolished concrete in civil engineering projects, such as transportation projects, can have a major effect on providing sand and gravel sources and solving some of the environmental problems. One of the performance characteristics of these kind of materials is their durability against continuous freeze and thaw cycles. Destructions due to this cycle are one of the durability problems for different layers in pavements in cold climates. On the other hand, considering the share of aggregates in road construction, it should be noted that durability performance of these aggregates against freeze and thaw cycles is important in performance of the layers. Up to now, different standards have been written for durability assessment of the aggregates against freeze and thaw cycles. But, due to the difference in structure of recycled concrete aggregates (RCAs) and lesser quality of these aggregates, compared to the natural aggregates (NAs), application of these standards for RCAs is questionable. Therefore, in this research, three standards of ASTM C 88, AASHTO T 103 and CSA A23.2-24A were selected to assess the durability of RCAs and NAs against freeze and thaw cycles. Water adsorption and abrasion tests in Los Angeles apparatus were conducted too. Results showed that AASHTO test has high destruction power and its application with temperature-time cycle in this experiment is not recommendable. Also, the aggregate soundness test, using magnesium sulfate test, is not applicable for RCAs and does not have reliable results. But, the CSA test has acceptable results, in accordance with the results of physical and mechanical tests.

In road design, pavement has detailed design and its cost is inevitable. But, in the infrastructure, the costs can be considerably reduced by optimizing the position of vertical alignment. One of the most expensive parts of the infrastructure is earthwork costs, which is highly dependent on the project vertical alignment. Therefore, the aim of this study was to evaluate various meta-heuristic methods for proposing a method for vertical-alignment optimization to have the lowest cost of earthwork operations. In this study, first, the objective function and constraints of the problem were formulated and then the distance, height, and length of the vertical curve in every point of vertical intersection (PVI) were considered as decision variables. Initial vertical alignment and position of the PVIs were defined according to the guidelines and demands. The objective function was defined as the sum of absolute difference of the vertical alignment height and ground surface. Meanwhile, the constraints were defined as minimum and maximum longitudinal slope, minimum height of the bridges, avoiding interference of the curves, and minimum length of the vertical curve. For optimization of the problem, Genetic Algorithm (GA), Accelerated Particle Swarm Algorithm (APSA) and Firefly Algorithm (FA) were used in the MATLAB software. For better evaluation of the developed method, three different topographies (plain, rolling, and mountainous) were designed and the original vertical alignment was optimized by each algorithm. In addition to the difference of vertical alignment and ground surface, comparison of the ratio of volume of fill to volume of cut, and earthwork costs, was carried out. Results showed that the highest optimiztion percentage for the three topographies belonged to FA, APSA and GA, respectively. Therefore, application of FA highly reduced the costs of road infrastructure. In addition, the time and replications needed to solve the problem show that the necessary time for optimization and obtaining the optimum solution is ignorable in comparison to the achieved cost saving.

Steel bars are widely used for reinforcing of structural concrete members. Although the steel bars have suitable application, but its deterioration and corrosion in aggressive environmental conditions such as reinforced decks or beams in bridges was displayed as a disaster. Replacing steel bars with Fiber Reinforced Polymer (FRP) bars is a good way to solve this problem, because FRP materials have high durability in acidic and aggressive environments. The influence of different parameters such as modulus of elasticity, section, and percentage of FRP tensile reinforcement on capacity, displacement and ultimate moment and the overall flexural behavior of RC decks and beams of bridges were numerically investigated in this paper.In order to evaluate the effectiveness of considered parameters with FRP, the behavior of 18 beams, reinforced with FRP bars, was simulated via finite element method. Results indicated that the ultimate capacity of beams reinforced with FRP bars was increased up to 16.45% due to increasing amount of longitudinal tensile bar percentage up to 73.62%. Also, after increasing the modulus of elasticity of FRP bars up to 35.3%, the ultimate capacity of beams was increased up to 9.75%. Therefore, application of FRP bars in bridges members can prevent probable deterioration and also increase load capacity.