مجله مهندسی زیر ساخت های حمل و نقل
پیاپی 2 (تابستان 1394)

In this research, it has been tried to correct the pseudo-static method based on seismic performance of hybrid soil nail/MSE walls as a newly developed method. Accordingly, the pseudo-static coefficient is introduced as a function of primary earthquake parameters such as predominant period, peak ground acceleration and cumulative absolute velocity, geotechnical characteristics in terms of site conditions and performance levels of system. In doing so, numerical analysis results with regard to performance levels of hybrid soil nail/MSE walls in various seismic and geotechnical conditions were taken into account. Subsequently, the pseudo-static coefficient corresponding to each of the studied numerical models was determined using limit-equilibrium analysis and the pseudo-static coefficients for performance levels were developed. The outputs are presented with reference to the site and seismic divisions separately according to Iranian Seismic Code (Standards No. 2800). Consequently, it is also shown that the choice of the pseudo-static coefficients for performance levels is highly affected by the type of the site and seismic conditions.

A large proportion of the national budget in many countries is spent each year on rehabilitation and reconstruction of highway and airport pavements. Low strength against dynamic loads and short working life of pavements are the most significant problems in the maintenance of highway systems. Rutting phenomenon is one of the main destructions which occur due to visco-elastic and visco-elasto-plastic behavior of asphalt mixtures at high temperatures. So far, a lot of laboratory research has been conducted to evaluate the effect of glass cullet on asphalt mixture behavior against dynamic loading of vehicles and environmental conditions. The purpose of this study was numerical evaluation of the effect of glass cullet on asphalt mixtures behavior and prediction of rutting phenomenon in them. ABAQUS software was used to achieve this goal. In order to validate the model results, wheel track test results were used. The results showed that the developed model can predict rut depth of glasphalt and asphalt mixtures very well. Also, evaluations on the model showed the high effects of glass cullet to improve the visco-elastic and visco-elasto-plastic behavior of asphalt mixtures.

To make a precise investigation of bridge pier strengthened with fibre-reinforced polymer (FRP) composites, two types of pier columns with rectangular and circular cross sections, retrofitted with various methods of composite wreathing, and under different loading conditions were studied using finite element method. Concrete was modeled employing the octal-nodular three-dimensional element with the ability to consider fraction under tension and failure under pressure.In order to model the longitudinal reinforcement, a bi-nodular one axial pressure-tension element was used. Cross bars were arranged as a percentage of volume in concrete element. The FRP composite material was modeled by using layered octal-nodular three-dimensional element. The results of this research demonstrated that with wreathing all around a pier column, the ductility and resistance capacity increases in both types of piers’ cross sections. However, more increase in the measured ductility and strength could be identified in rectangular and circular sections, respectively.

Rutting is one of the most important deteriorations in flexible pavements and a significant amount of annual maintenance and rehabilitation funds are spent for its repair. Permanent deformations increases, which leads to increasing rut depth, can cause irrepairable problems in asphalt pavements. On the other hand, in Marshall method, which is known as the main method of asphalt mixtures mix design in Iran, the lack of a simple test to determine specimen resistance to permanent deformation is sensible. Although there are many devices to measure the rutting nowadays, but none of them have the ability to be used at site level. In addition, prevalent methods of evaluating rutting potential of asphalt mixtures are usually expensive and time consuming. The abovementioned factors necessitate development of a simple laboratory method that not only enjoys an acceptable precision but also is able to predict specimens rutting performance with low cost within the short time. In this research, one type of aggregate, one type of gradation, two types of bitumen, one type of filler, and three bitumen contents were used to prepare Marshall asphalt mixture specimens. After performing the main tests on specimens, IDT test results and Marshall parameters were used to develop a mathematical model to estimate specimen Wheel Track apparatus rut depth. The presented model measures rutting resistance using a combination of indirect tensile strength test results and Marshall parameters. The model is validated using artificial neural network, which makes it possible to evaluate rutting potential while OBC is being determined in a laboratory. Therefore, not only is there no need for expensive instruments of rutting test, but also a remarkable time saving in mix design procedure is achievable.

Fatigue cracking is perceived as one of the primary failures in asphalt pavements. This type of failure originates from the bottom of asphalt layer and then spreads upward as a result of repeated loading. Emersion of this type of cracks is common in asphalt sections with less thickness. In this research, for a better understanding of the mechanisms and parameters of fatigue cracks propagation, the fracture mechanics approach was used. Subsequently, the crack phenomenon and its extension in pavements were theoretically analyzed under three temperatures: low, medium, and high. The results showed that the stress intensity factor is directly correlated with the distance of loading from the center of the crack. Moreover, stress intensity factor was observed to increase more rapidly when the load is applied near the crack in case of having granular base compared to concrete base. This highlights the high impact of type of base, especially granular base, when it comes to changes in stress intensity factor.

Porous concrete is a special kind of environment-friendly concrete with high porosity, which is used as pavement in low traffic-volume areas. Due to porous nature of this pavement, road surface runoff and traffic noise will be reduced remarkedly. As collecting and disposal of rice husk in agriculture is a source of pollution and is generally burned, its recycling may cause reduction in cement consumption and conservation. In this paper, a combination of sand and rice husk ash was used for concrete pavements to strengthen cement paste and polyphenylene sulfide fiber to improve strength properties of porous concrete. Concrete specimens with different water to cement ratios were built and tested to determine mechanical properties of porous concrete. Based on the results, only sand had low effect on mechanical properties of the porous concrete. But combinaton of sand, rice husk ash and fiber significantly affected mechanical properties of the porous concrete.

Accumulation of waste materials resulting from industrial production and daily life in big cities has become a major problem. Using these materials in road infrastructures is one of the solutions to this problem. Scrap tires (crumb rubber) and waste glass (glass cullet) are among waste materials whose effects on rutting resistance of stone mastic asphalt are evaluated in this research. Evaluation of rutting resistance of stone mastic asphalt (SMA) mixtures containing crumb rubber (passing through No. 200 sieve) and glass cullet (passing through No. 30 sieve ) is conducted by the dynamic creep test. The gap graded aggregate, asphalt cement with 60-70 pen, and additives (crumb rubber and glass cullet) with different percentages were used to fabricate the SMA mixtures. The results of the dynamic creep tests showed that rutting resistance of SMA mixtures containing aforementioned additives was improved in comparison with conventional SMA.