مجله پژوهش های زیرساخت های عمرانی
سال پنجم شماره 2 (پیاپی 9، پاییز و زمستان 1398)

Bridges are considered as important structures in the essential arteries of life. In recent earthquakes, the necessity to retrofit the structure of bridges has become apparent as an undeniable truth. In Iran and in recent decades, the engineering community has been trying to adapt itself to the regulations of the world. In the 1990s and early 2000s in Iran, the behavior of bridges has been considered under gravity loads more than their seismic behavior. Most of the bridges being used lacked the appropriate standard administrations for preserving the earthquake functions. To this end, the current study has focused on the evaluation of concrete frames ‘behavior of high-ways' common bridges in Iran. Accordingly, two types of concrete frames with the existing details according to the average of several bridges having different pier numbers under the lateral loading, have been investigated. Moreover, the knee and mid joints' behavior have been compared step by step. The performance evaluation of these bents illustrated the need for seismic improvement for desirable Failure mode, and the process of damages and performance levels of components had shown an unsuitable failure mechanism. Also, the quantitative values of indices of damage have been studied separately, which can be used in future studies.

Reliability theory is a part of the general theory of probability that earned a special place in engineering science over recent decades. This theory has a logical framework. It provides the actual safety assessment possibility of a system by analyzing the uncertainties using mathematical methods. These uncertainties are caused by the statistical nature of engineering problems. Reliability is a scale that can measure the probability of failure or safety of a system. So far, various methods have been proposed to estimate the probability of failure of a phenomenon. MCS is one of the most important and most widely used approaches in this field. Many steps will be removed by providing a simple and effective method. The data generated in this method is based on the histogram. SGH, there is no need to curve fitting test. This method is very useful in case data on the studied phenomenon be available in sufficient number, and continuous histograms could be created. The general performance of SGH is passing the histogram of uniform data scattered in three-dimensional space and select samples in the diagram area. As well as, it provided three practical examples. The first one is estimating the failure probability of a concrete beam under moment load with four random variables. The second example expressed failure probability of a steel beam, and the third one is about sliding and overturning failure of SHAFAROUD concrete gravity dam. Results were compared with the usual method of sample generation and indicated the effectiveness and accuracy of the responses of the proposed method.

The purpose of this study is to identify the most vulnerable pier in a real bridge sample using the tensor method. Therefore, after modeling the Kordestan-Mullasadra Bridge as one of the most vital arteries of the transportation system in Tehran in OpenSees software, the signals recorded by displacement sensor at the control points of the bridge, before and after the earthquake event were subjected to the action of a sine wave load of 5π angular frequency, using RID functions in Matlab software were processed. Then, the 2d matrix of time-frequency and 3d plan of time-amplitude-frequency have been studied for all piers of the bridge. By calculating the difference of the time-frequency matrix before and after damage and normalizing the responses, the most vulnerable pier is identified. In order to ensure the accuracy of the output results, by creating the damage pattern at the pier1 of FHW04 bridge, the damaged pier is detected by acceptive accuracy according to the method used in this study. The results of this study indicate that the most vulnerable pier of Kordestan-Mullasadra Bridge is based on signals recorded by the displacement sensor, the pier number 8 with the failure index 1. Respectively the pier number 7 with the 0.548 failure index, the pier number 2 with the 0.433 failure index and the pier number 6 with the 0.255 failure index are ranked next to the most vulnerable middle pier of Kordestan-Mullasadra street bridge.

Fiber reinforced concrete in tension is categorized based on tension softening behavior. Wide researchers have been studied this behavior and presented many tension softening models. With regard to the difficulties in direct tension test, tension softening diagram will be obtained a base on reverse analysis of flexural or split wedge test. The result of the inverse analysis method is mainly affected by applied assumptions. In this research, a new method which combines the finite element and section moment-curvature relations is presented. This method is called FE-SMC. In this study, the three-point bending test has been stimulated by this method. In each step of loading, the nonlinearity of cracked section properties have been calculated with moment-curvature relationships and the parameters have been updated in FE. The arc length method has been used for iterations solution. Finally, this method is validated with some experimental test results. The results show that FE-SMC method show desirable result for low-fiber content with descending tension softening diagram. Also using this method in some experimental results with constant tension softening or hardening behavior, do not meet the required fitting criteria and show deficiency in applied assumption and need to modifications.

Delay in construction projects is one of the most common problems. That will increase contract costs, increase construction time overestimated, increase project current costs and time lost due to lack of timely operation. Considering the importance of delay and time-increasing factors more than predicted, it is necessary to investigate and analyze its factors. In this paper, the identification, qualitative and quantitative prioritization of execution stage delays in road construction projects from the risk management perspective in the Garmsar-Simindasht road have been studied and evaluated. Identification of risks by structured interview technique, qualitative risk prioritization by expert opinion survey, and quantitative risk prioritization by analytical hierarchy process technique. Its outputs are qualitative delayed risk prioritization with cause and effect (Ishikawa) charts and quantitative risk ratings with Expert choice software. According to quantitative ranking, financial and credit problems, lands’ appropriation, management problems, technical problems and natural disasters have the highest risk among the main criteria. Among the sub-criteria of the risk, incomplete allocation, land price, gardens, incomplete feasibility studies, incorrect timing schedule, provincial credits, no money deposit, residential areas, commercial areas, agreement with the natural resources, agreement with the environment, flood, low initial estimate, national credits, industrial areas, unfavorable weather conditions, ground operations, asphalt problems, accident insurance have priority. Finally, Critical criteria analysis performed and solutions have been proposed to reduce or eliminate the effect of these delays in road construction projects.

In this paper, two models have been developed to predict the resilient modulus of asphalt mixtures reinforced with Korta fiber subjected to square and haversine waveform, based on the response surface methodology. To this end, the asphalt mix samples were fabricated with three different percentages of bitumen and four different percentages of Korta fiber and then the resilient modulus was measured at five temperatures, five loading frequencies and two loading waveforms (squared and haversine), using UTM 30 apparatus. In this study, temperature, loading time, bitumen percentage and fiber percentage were considered as inputs variables and the resilient modulus under haversine and square loading waveforms was considered as output variable. The results of this study show that the response surface methodology is able to predict the resilient modulus of fiber reinforced asphalt samples with high accuracy, so that the regression coefficient of the developed equations for the haversine and square loading waveforms is 0.9795 and 0.9777, respectively. Also, the results of the sensitivity analysis show that increasing fiber percentage to a certain amount increases the resilience modulus and increasing the fiber content to more than this percentage, decreases the resilient modulus. This study also shows that the optimum percentage of Korta fiber depends on the bitumen content in the asphalt mix. So that in asphalt mixtures with higher bitumen percentages, the optimum fiber percentage was less (about 1 kg/ton) and in mixtures with lower bitumen percentage, the optimum fiber percentage was higher (about 1.5 kg/ton).

Due to the importance of maintenance and repair costs, the quality of the asphalt quality is of particular importance. Bitumen is one of the most important components of asphalt mixing. It is essential to select the appropriate type according to the weather and traffic conditions of each area in order to increase the quality and durability of the asphalt. A study based on the Sharp method in the bitumen classification on a different level of confidence can provide optimal results with the combination of technical and economic conditions. In this research, using the statistics of the meteorological stations of Hamedan province, the performance index is PGXXYY at four levels of confidence of 50, 84, 98, and 99.9 percent, and considering the traffic conditions in the main roads of the province. Based on the results of the research, at lower levels of confidence, more low-grade bitumen will be more covered, and with increasing confidence, the role of the bitumen will be higher in the higher category and at a certain level of certainty the applied traffic conditions of the category of functional bitumen used in increasing zoning Based on this research, it is necessary to zone the functional index of bitumen at the country level in terms of weather conditions and traffic at different levels of confidence level in order to determine and select according to the technical and economic principles of bitumen consumption.

Due to the limited soil resources and population increase, the use of contaminated or problematic soil is inevitable. There are different methods to improve the geotechnical properties of clay soils. One of the ways is to stabilize the soil with stabilizers such as Portland cement and lime. Investigation of the combined effect of organic pollutants under the influence of stabilizers (Portland cement (I) and lime) on Kaolinite clay using modified Proctor and CBR experiments constitutes the present research framework. The maximum unit weight decreased with an increase in Anthracene content while its variations were strongly dependent to the Glycerol content. The maximum of dry unit weight and a minimum of optimum water content occurred at a glycerol content of 6%. Based on test results, it was found that the increase in strength of clean Kaolinite using 6% of Portland cement is equivalent to that of 30% lime. It was also found that the contaminants decrease the strength of kaolinite; however, both stabilizers increase it. The effect of Portland cement on the strength of the specimens contaminated with Anthracene was better than that of lime and the effect of Portland cement and lime on the improvement of samples contaminated with Glycerol was considerable.

Utilizing of fiberglass nail in the face of tunnel is one of the economical and effective pre-support methods for increasing stability and control of settlement in weak grounds and tunnels with extended level and increase of ground mechanical strength. In this study, by taking advantage of 3D modeling of fiberglass nail which is effective in reduction of deformation, settlement, the direct modeling of nail in the 3D finite element and material with equivalent section. This study has covered effects of nail density, the overburden to depth of tunnel ratio. The method of strength reduction for analyzing the safety factor of tunnel has been considered. The result of 3D numerical analysis with limit equilibrium methods (LEM) for determining safety factor has been compared. The comparison of LEM and finite element method revealed that using of nail fiberglass and increases the range of safety factor between 5% to 75% and 1.25 to 2 in terms of overburden to diameter ratio. This increase of nail is dependent on density and overburden. While, with increase to advance length, the amount of vertical displacement would rise in both method, although these measures have no effects in horizontal displacement. In addition to that, using of nail in the tunnel face has caused the amount of vertical displacement between 20 to 35 percent and in the horizontal displacement between 50 to 60 percent of decrease has happened.

The purpose of this research is to investigate the performance and efficiency of reinforced slope in the stability of geocell layers in unsaturated soil conditions. Slope reinforced with geocell, due to the fact that the geocell has a height (three-dimensional), acts as a beam in the soil, and because of its flexural properties, it has a moment of inertia as well as bending strength, which reduces the displacement and increases the coefficient reliability of the slope. Considering unsaturated conditions of soil contributes a lot to make results close to reality. One of the well-known models among elastoplastic mod-els for modeling unsaturated soils is Barcelona's basic model, which has been added to the FLAC2D software by codification. Changes in thickness, length, and the number of geocell layers are remarkably effective on slope stability. The results show that the geocell's reinforcing efficiency depends on the number of layers and the depth of its placement. As the depth of the geocell's first layer increases, the lateral and vertical side elevation of the upper part of the slope increases with respect to the elevation. Load capacity increases with increasing geocell length. By increasing the length of the geocell lay-er, the joint strength, the tensile strength of the mobilized, and the bending moment are increased. Also, by increasing the thickness of the geocell, the amount of moment of the inertia increases, and as a result, the amount of geocell reinforcement bending moment increases.

In this study, the behavior of Marvak Rockfill Dam with clay core by 68 m height by using numerical modeling by GeoStudio software and monitoring results have been evaluated. In the first step of this study, Marvak dam has been numerically modeled by GeoStudio software and vertical stresses in the core and maximum settlement during construction have been determined. At the next step, results have been compared with monitoring results in the various parts of the dam. Comparison of the numerical and monitoring results depicted that at the elevation 1590 m, 31 m lower than the crest, the maximum settlement in the instrument INC 10 in which located 4 m upstream of dam body is 810 mm and numerical results is equal to 800 mm. Maximum settlement in the long term and arching occurs in the middle of the dam approximately. The value of the arching ratio is between 0.73-1 which indicates that Marvak Dam is in stable condition.

One of the major challenges in dam engineering is the design of the discharge flow of the stepped spillway. The rate of energy dissipation in downstream currents is higher than that of skimming currents. To achieve this goal, the discharge and skimming slope of the spillway must be low, which makes it economically efficient and applicable. For this reason, in the design process of spillway discharge, flow is assumed to be skimming. In this study, after validation of the Flow-3D model, the discharge flow of the Siah Bishe spillway was simulated. For validation, the values of the flow-Ashle curve were evaluated, and the root means square error of 5.07 was obtained. According to the results of numerical simulation, the flow must be at least 17 m3/s for the discharge. As the flow rate increases, the flow will discharge and move into the state of transient flow, which will continue to flow with 37 cubic meters per second. Finally, for values of more than 60 cubic meters per second, the flow is definitely skimming.