مجله مهندسی زیر ساخت های حمل و نقل
سال دوم شماره 2 (پیاپی 6، تابستان 1395)

A suddenly change and non-uniform track vertical stiffness along the railway track among bridges transition zone increased dynamic loads, deformations asymmetric ,bumpy rails, damage track components and train and so maintenance costs are increasing. One of the methods used to solve these problems is creating approach slab around the structures and bridges. So this paper Optimization Dimension of Concrete Approach Slab in Transition Zone for Railway Short Span Bridge studied according to the vertical displacement rails, vertical displacement ballast layer and normal stress distribution in the middle layer of ballast. For this purpose finite element model of the ballasted track and bridge is created and verified. results show that in transition zone for railway short span bridges length of 6 m, a thickness of 50 cm and a slope of 5% are as optimal geometric parameters for the approach slab. So vertical displacement track and vertical displacement ballast layer with optimal approach slab respectively to 24% and 18% are decreased and the contrary normal stress distribution in the middle layer of ballast 40% is non-uniformed but normal stress is under level allowance stress for ballast layer

One of the important factors that could increase the life of asphalt pavement is proper implementation of asphalt layers. Binder and Topeka layers are some of the first layers related to the weight of vehicles which are connected by surface dressing. Passing of vehicles leads to create shear force in the adhesive area between the two layers, which in the absence of sufficient strength, this shear force causes damages such as shrinkage, longitudinal and transverse cracks and creates depressions on the pavement surface. This research has been performed as laboratory experiment and numerical modeling process. In the laboratory process, samples were constructed in Binder and Topeka layers and then contaminants such as crumb rubber, sand, wood chips and fibers were used in the surface dressing between the two layers to study the effect of each contaminant on inter-layer adhesion resistance. The samples were held by a jaw holder in order to fix the Binder layer, and then were put under the influence of vertical force of shear load machine situated in the Topeka area. In the numerical modeling process, the samples’ pavement was modeled for real conditions. In this process, the road surface was modeled and the passing of vehicles was simulated, and then the existence of the contaminants between the Binder and Topeka layers were evaluated. In the modeling process, by varying the thickness of Binder layer, velocity of passing vehicle and adhesion coefficient between the Binder and Topeka layers, the inter-layer adhesion force in the created situations was investigated. Based on the test results, among the investigated cases, the created sample with lower limit of gradation, which used crumb rubber as a contaminant between the Binder and Topeka layers, by increasing the resistance to 1.1 times more than the bitumen without contaminant, not only didn’t decrease the inter-layer resistance, but also had the greatest adhesion strength.

Nowadays, due to the human need for transportation and growth of tire industries, huge volume of used tires are discarded annually to the environment. Therefore, many researches have been performed for their reuse. In the present research, effect of using crumb rubber on the roller compacted concrete (RCC) pavements has been studied and the main characteristics of the concrete such as density, compressive strength, flexural strength, and water absorbtion were evaluated. Therefore, natural aggregates were replaced in the concrete by crumb rubber with similar size to sand particles, in different percentages (5, 10, 15 and 20 percent). Based on the results and former studies, and contrary to the reducing effect of crumb rubber for strength, using crumb rubber particles in RCC, up to a certain level, could increase compressive and flexural strengths. Also, crumb rubber particles decreased water absorption of the concrete specimen. Results showed that increasing the percentage of crum rubber particles in the concrete reduced the amount of absorbed water.

In the last decade, porous (pervious) concrete has been used in sidewalks and surface pavements for collection of urban runoff water. Porous concrete is highly considered for its hydrailuc conductivity and water transport capacity. In the present research, the original porous concrete was made of 1400 kg/m3 aggregates and 330 kg/m3 Portland cement, along with water to cement ratio (W/C) of 0.35-0.45. In the mixture of porous concrete and additive, the following additives were used: zeolite, perlite, pumice and clay aggregate, with type 2 and type 5 Portland cement. Compressive strength and permeability coefficient (hydraulic conductivity) were studied. Results revealed that adding additives decreases compressive strength of the porous concrete. This reduction in compressive strength for the highest and least amount of zeolite, perlite, pumice and clay aggregate was 13, 48.4, 10.1 and 12.6 percent, respectively. Hydraulic conductivity increased in most of the treatments, except perlite. The highest increase in hudraulic condictivity (7.3 %) occurred in the treatment containing 5% pumice and the highest reduction in hydraulic conductivity (3.7 %) occurred in the treatment containing 10% perlite. In general, among the different additives used in this experiment, the treatment containing 10% perlite had the highest compression strength (11.95 MPa) and the treatment containing 10% clay aggregate had the lowest compression strength (3.2 MPa). This shows that adding clay aggregate reduces compression strength of porous concrete more than other additives. The perlite additive ranks next.

Growth of traffic factors such as high traffic volume, travel of heavier vehicles with more tire pressure, demand higher-strength asphalt mixes. Researches in recent decades have shown that using polymers and fibers in asphalt mixes has delayed failures and improved properties of the asphalt pavements. In this research, effects of ethylene vinyl acetate (EVA) polymer on the fatigue behavior of bitumen and asphalt mixtures are investigated and analyzed. So, linear amplitude sweep (LAS) tests and elastic recovery of bitumen are used to characterize fatigue behavior of bitumen and the four-point bending beam test is used to measure fatigue life of asphalt mixtures. Elastic recovery results showed that modifying bitumen with EVA enhanced elastic and recovery properties of the bitumen. The LAS test data showed that modified bitumen has better resistance against high strain and slows down the growth of failure trend. The results of LAS test showed that EVA-modified bitumen improves the viscoelastic properties, performance and fatigue behavior of the bitumen. Also, comparison of the results of this test at 20 and 30 °C showed that pure and modified bitumen have higher fatigue life and better fatigue resistance at 30 °C. By increasing the temperature, bitumen becomes softer, its viscoelastic behavior is revealed better, and recovery of thin cracks, caused by loadings, is faster. Also, results of beam fatigue test showed that the modified mixes with this polymer have higher fatigue life, compared to pure bitumen specimen.

Bridges are very important and vital structures in any country and have main roles in transportation. Collapse of bridges due to earthquakes in San Fernando (1971), Northridge (1994), Hanshin (1995) and Chi-Chi (1999) showed that there are still many unknown and unsolved problems in seismic design of bridges. In this research, an existing overpass bridge in Urmia was analyzed by nonlinear dynamics, using SAP2000 software, and its dynamic response has been investigated with different kinds of seismic isolation systems (elastic neoprene and LBR isolators), considering the effects of soil structure interaction. One of the important tasks in this project is modeling the abutment backfill of the bridge which can affect its response depending on the type of bridge isolation. To perform a time-history dynamic analysis, this research uses near-field and far-field earthquakes records to compare the bridge response affected by these earthquakes. Results of the analysis showed that LRB isolators would increase deck displacement and decrease pier and abutment displacement, as compared to elastomeric isolators, and also decreases the soil-abutment interaction. On the other hand, bridge isolation causes a decrease in forces and better distribution of shear force between abutment and piers. Also, the abutment backfill would dissipate some parts of the earthquake energy. The decrease of the earthquake shear force in non-isolated models is more than the isolated ones. On the other hand, by comparing the periods of absence of proper distance between superstructure and infrastructure in the expansion joint position, it follows that this parameter is 0.52 in model E and about 0.36 in E-S. If there is sufficient distance between superstructure and infrastructure in the expansion joint position, these values increase to 0.89 and 0.87, respectively.

Moisture susceptibility, mechanical deformations, freeze-thaw cycles and penetration (in winter maintenance operation) into asphalt mixture are important mechanisms that cause various failures in asphalt pavements. In recent years, using polymeric sulfur compounds (Googas) has been the focus of attention for many researchers due to the ease of availability and low cost, as well as the observance of environmental principles. Based on the previous studies, it has been found that asphalt mixtures containing Googas are weak in the presence of moisture. In this research, the effects of hydrated lime and sasobit additives on moisture susceptibility, mechanical strength and resistance against freeze-thaw cycles in asphalt mixtures containing Googas have been investigated. First, the mentioned aggregates, bitumen and additives were prepared and the required tests were performed on them. After determining the optimum bitumen percent by Marshall method, the moisture susceptibility, mechanical deformations and resistance against freeze-thaw cycles of asphalt mixtures were examined using parameters of tensile strength ratio (AASHTO T-283) and Marshall quotient (ASTM D-1559). Based on the results obtained from the tests, it was found that sasobit additive effectively improved the resistance of control asphalt mixtures, and mixtures containing Googas, against moisture and freeze-thaw cycles. However, hydrated lime additive had no significant impact on improving the items mentioned characteristics. In general, and statistically, asphalt mixture containing 30% Googas and 1.5% sasobit offered the best result in improving the resistance of asphalt mixtures against destructive effects of freeze-thaw cycles.