مجله مهندسی زیر ساخت های حمل و نقل
سال چهارم شماره 4 (پیاپی 16، زمستان 1397)

In order to reduce fuel consumption and CO2 emission in producing and paving asphalt concrete, the warm technology has gained a lot of interests in the recent years in academia and/or industry. In this research study, three warm additives (Sasobit, Rheofalt, and Zycotherm) were used to modify original binder (60-70 penetration grade. (The test data are used to assess the stress sensitivity of asphalt binders at different percentages of additives. The binder fatigue and rutting performance was evaluated through Linear Amplitude Sweep (LAS) and multiple stress creep and recovery (MSCR) test, respectively. The multiple stress creep and recovery (MSCR) test was used to determine the percent recoveries (R), the non-recoverable compliances (Jnr) and the percent differences in non-recoverable compliances (Jnr-diff) of these modified asphalt binders. Results indicated that 3% Sasobit modified binder has the highest percent recovery value and the lowest Jnr value, but had the highest sensitivity to a sudden increase in the stress level inside the asphalt mixture. Unlike the other asphalt binders, the rheofalt and zycotherm modified binders showed small increases in R and slight decreases in Jnr at 64°C temperature. The LAS test results demonstrated that for low strain levels, the fatigue behavior of asphalt binders modified with 1% Sasobit, is the highest one. However, for high strain levels, the 2% Rheofalt had a better fatigue behavior than the other modified binders.

Today, energy absorbers are used to reduce the damage caused by collision. Thin-walled structures are the most popular energy absorbent and is used in various forms. Thin-walled tubes due to lightness, high value of impact energy absorption, long crushing length and high ratio of energy absorption into weight have ever-increasing application as one of the effective energy absorption. The purpose of this study was to investigate the effect of geometry deformation on the energy absorption of brass tubes with square cross-section and the effect of combined bitubular tubes to absorb more energy under Axial Loading. In the experimental part, brass tubes with square cross-section were prepared and then the quasi-static tests with static loading rate were performed and the load-deflection diagrams in each test were obtained. A numerical model is presented based on finite element analysis to simulate the collapse process considering the non-linear responses due to material behavior, contact and large deformation. The comparison of numerical and experimental results showed that the present model provides an appropriate procedure to determine the collapse mechanism, crushing load and the amount of energy absorption. The validated finite element model was then used for the parametric studies, in order to determine the effect of the geometry parameters (i.e. imperfection and thickness) and dynamic loading parameters (i.e. impact mass and impact velocity) on the energy absorption.

Population growth and the attributed increase in housing demand are the cause of an acute shortage of suitable land for construction. As such, it has become a business strategy in construction sector to find optimum solutions in terms of modification and improvement of inferior lands. One readily available solution to address this issue is decreasing the settlement of strip footings and improving their load bearing capacity through embedding cemented zeolite pads underneath the strip footings. Therefore, here, a series of small scale 1g model tests have been conducted with the aim of evaluating the behavior of the strip footings reinforced with zeolite-cemented pad. For practical purposes, Babolsar sand (in dry and saturated conditions) has been selected as the case study. The pads are placed underneath the foundations and in direct contact with the sand. The results demonstrate that placing a pad with one third thickness of the foundation's leads to an increase in the bearing capacity of both dry and saturated conditions. This increase is in the range between 30% to 91% under the dry condition and between 23% to 67% under the saturated condition. Also, this reinforcement causes clear increase in settlement reduction ratio of the dry condition in the range between 35% to 60% and in the 29% to 49% range for the saturated condition.

In recent years, a large number of researches in the field of pervious concrete pavement have been done because of major environmental benefits. The existence of void space in pavements reduces their strength and durability. This problem causes these pavements to be used in some places with low traffic volumes such as sidewalks, driveways, parking lots and residential roads. In this kind of concrete, aggregates play a key role regarding its performance, so using aggregates with suitable properties in concrete, improves its performance. Copper slag is a by-product resulting from the production of copper metal. Using this production in concrete can be considered as an appropriate solution for its environmental problems. In addition, it can improve the performance of concrete mixtures. In this research, the effects of copper slag on some physical characteristics of concretes have been investigated and analyzed.In this research, two types of aggregates of dolomite and copper slag were used, crushed copper slag gradually was replaced by coarse aggregates of the mixture. Totally seven main mix designs were used with 0 to 100 percent of copper slag. In order to analyze the effect of this aggregate on the performance of pervious concrete, the physical and mechanical properties of these mixtures were investigated. The results indicated that using crushed copper slag causes the unit weight of concrete to be increased because of high specific gravity of copper slag. Also, by gradually replacing of copper slag, void ratio and permeability are increasing due to apparent characteristics and low absorption copper slag than dolomite aggregate. Moreover, the results of compressive, flexural and split-tensile strength tests showed that Adding copper slag has improved this properties and the C60 has the highest increase in comparison with control mix design.

The design of standard bus stations is one of the most important issues that increase bus performance at the stations, reduce the take-off time and take passengers, and less negatively influence the traffic on other vehicles. In this research, we tried to find suitable locations for establishing subway station candidates in the city of Tehran 6 with GIS functions and ANP network analysis decision making. Using genetic algorithm and target functions, we aimed to optimize the candidate stations. In order to increase the accuracy of the research, the study area was divided into two areas of strong and weak concentration of service centers and commercial centers. the results showed that according to the network length and station spacing standards, area 6 requires 306 to 208 stations. Of the 291 stations, 247 stations, and 212 existing stations, 147 stations were optimized they can maximize demand coverage for demographic centers and absorbent centers.

In today`s world urban railway is one of the important transportation systems that should be examined against various environmental phenomena including fire condition to service permanent citizens. Usually construction of concrete segments of the tunnel simultaneous to used high strength concrete (HSC) that have bad reaction under fire in spite of good seismic reaction. When a fire occurs in tunnel surrounding, some interaction occurred in concrete segments of the tunnel that can reduce the thickness and decrease the safety of these segments. Most of the researches in applying heat effect on concrete segments of the tunnel are experimental and under this situation and analytical or numerical researches in this issue are low. This paper presents an analytical model using ABAQUS software based on the finite element for evaluating concrete segments of tunnel behaviour under fire condition. To ensure the safety of results, some fire curves are applied and effect of Polypropylene fiber in the concrete mix is evaluated. Results show that adding minimum 0.9 Kg per cubic meter of concrete mix in concrete segments of tunnel causing loss of spalling and improve fire behavior interaction.

Determining the model of railroad degradation can play an important role in preventing failures and, consequently, reducing maintenance costs in the railway industry. Railroad deterioration model is known as the most practical of such models. However, current deterioration models are static models that focus only on the independent effects of some of the parameters affecting deterioration.This paper proposed a new railroad deterioration dynamic model based on System Dynamics (SD) theory. SD as a scientific attitude analyzes the system's behavior over time through its feedback structure. The proposed model, in addition to studying the simultaneous effects of different parameters, evaluates the railroad deterioration dynamically.Implementation and validation of the proposed model of deterioration, using a real example of Iran's railways, indicates the accuracy of the obtained results. Another great consequence of proposed dynamic model is determining the deterioration function in terms of time in Iran railway. This function can be used to predict the deterioration of the railroad in future periods. This function has the ability to configure to other railway networks in the world.