نشریه مهندسی عمران مدرس
سال بیستم شماره 3 (امرداد و شهریور 1399)

The utilization of concrete Incorporating with fibers is one of the proper issues of construction industry in last years. The main focus of this research to design a high performance self-compacted fiber reinforced concrete (SCFRC) by using an evolutionary algorithm, which is implemented in MATLAB. Crow Search Algorithm (CSA) and Genetic Algorithm (GA) are statistical ways which are developed by optimization based meta-heuristic solutions. A total of 67 concrete mixtures were considered by varying the levels of key factors affecting concrete strength of concrete, namely, water content (137.2-195 kg/m3), cement content (325.5-520 kg/m3), coarse aggregate content (722-920 kg/m3), fine aggregate content (804.9-960 kg/m3), nano silica content (0-49.6 kg/m3),percentage of volumetric of fibers (0-0.9 %), lime stone powder content (0-288.9 kg/m3) and superplasticizer content (1.75-10.5 kg/m3) were developed to design optimized mixture proportions. The objective function called maximizing concrete strength was formulated as an optimization problem on the basis of Multiple Linear Regression (MLR) method. The constrains including ratio of mixture proportions and absolute volume of mixture design were utilized to obtain an optimal-strength and cost-effective design. The concrete technological constraints were identified as the factors of experimental design for concrete production. The evolutionary implementation of results reached incorporating mixture proportions having strengths in range of 30 - 88.7 MPa. Five numerical examples for optimum mixture design of SCFRC were considered to evaluate the capability and efficiency of CSA and GA algorithm. These results were compared and concluded that CSA (3.38-14.49 % of mean error) performed better than GA (7.95-15.52 % of mean error) for this application. Also, the proposed evolutionary CSA and GA algorithms are found to be reliable and robustness tools to solve and optimize engineering and concrete technological problem.

In the recent years the use of phosphate fertilizer has been increased. On the other hand, the use of phosphate fertilizer causes change in micro-structure and geotechnical properties of clayey soils. This may raise the risk for groundwater contamination. The main objective of this paper is to study the permeability and microstructural change of clayey soils after interaction with phosphate fertilizer. To achieve the above mentioned objective, series of geo-environmental engineering experiments was performed and the process of interaction of bentonite with phosphate fertilizer is studied. The evaluation of permeability variations, sedimentation tests, plasticity properties, soil pH variations and results of XRD and SEM experiments show that the presence of phosphate fertilizer changes the clay soil microstructure. Based on the results of this study phosphate fertilizer causes a reduction on the quantity of intensity of basal spacing of montmorillonite. Consequently the permeability might increases around1000 times at the presence of 10 percent phosphate fertilizer.

The aim of this study was to investigate the removal of acid orange 7 from aqueous solution using a new triple nanocomposite biochar/ZnO/SnO2. In this experimental study, weight percentages of ZnO, weight percentages of SnO2, pH, dye concentration and nanocomposite dosage as effective parameters on removal of acid orange 7 using one factorial method were analyzed. The maximum dye removal efficiency of 96.92% obtained at optimum conditions, 20% weight ratio for ZnO, 5% weight ratio for SnO2, pH = 7.1, 250 ppm dye concentration, 0.5 g/L nanocomposite dose after 60 minute. One of the highlights of the nanocomposite was its high power to remove dyes in a very short time. As after 2 minutes of testing, most of the dye (about 86%) was removed. It was also observed that the nanocomposite had the ability to reduce COD by 77.27% and TOC by 66.6% after 2 hours. Also, nanocomposite was reused until the fourth time, when the efficiency reduction for the first to fourth times was less than 10%. According to the results, the kinetics of the reactions for the nanocomposite were in accordance with the double exponential model and the Langmuir isotherm model was the most consistent with the observed data. Also, according to the thermodynamic studies, the dye adsorption on the surface of the nanocomposite was physical.

According to the vital role that bridges play in transportation system and also communications of a society, monitoring their structural safety and keeping theme in service is crucial. Numerous methods have been proposed for detecting probable damages in bridges. Unfortunately most of them are based on comparison between the response of bridge in an intact and damaged state. Therefore intact state response must be known. However, not always it’s true in practice. So proposing a method which can determine and localize damages without prior knowledge of intact state is necessary. Such a method which was proposed by Sun et al. is studied carefully. Through the aforementioned method, the dynamic displacement response of a simply supported beam was decomposed into a dynamic component and a quasi-static component. Using Maxwell-Betti law of reciprocal deflection, the quasi-static component was attributed to the static deflection of the beam. Later damage which is defined by loss of stiffness, could be localized based on the abrupt changes in the static deflection curvature as it is related to bending moment and flexural stiffness of a beam. It is found out that the decomposition approach proposed by Sun et al. is restricted to fact that only one mode of oscillation must be dominant and also the natural frequency of motion must be determined through experimental measuring. Another limitation is that the abrupt changes in the curvature diagram cannot be related to damage essentially as curvature is also affected by the bending moment. In this study two modifications were proposed to get more accurate results in localizing the imposed damages. The first modification is the use of EMD method in order to decompose the displacement response into its intrinsic mode functions. Hence the aforementioned method could be used in real bridge displacement responses as higher modes corporations can also be determined and extracted through EMD process and finally the quasi-static component is determined as the residue of EMD algorithm. Also the ambient noise may be decomposed from the original signal, improving the method to work in real situations. The second modification is creating an imaginary constant moment length in the beam by the use of super position principle. So sudden increase in the curvature diagram is essentially a damage. Different scenarios of damage were studied and both methods have been used to detect damage in each scenario. Results show a great improvement in detection and localization of damage using the improved algorithm rather than the original proposed method. Eventually a five span real bridge model was taken into study. The improved damaged detection method could clearly determine the longitudinal position of the damage.

Every year with the expansion and development of industrial and mining activities, millions of tonnes of toxic waste are produced throughout the world. Soil contamination by organic material as a result of various incidents and the leakage of organic compounds into the soil solid porous media will have an adverse effect on the environment. There are several methods for soil remediation contaminated with hydrocarbon compounds. Electrokinetic is one of the effective remediation which includes three main mechanisms for remediation, electroosmotic flow, ionic migration and electrophoresis. Electrokinetic is suitable in terms of cost and time for solid and porous fine-grained environment media that have high adsorption capacity of moisture and also organic pollutants. Kerosene is considered as one of the hydrophobic organic compounds with harmful physical and chemical properties to ecosystems and high adsorption onto the water and soil media. It has different hydrocarbons in its composition, each molecule having an average of 10 to 16 carbon atoms. It is so durable in the ecosystem, including the soil environment. The soil used in this study was fine-grained kaolinite due to the nature and effectiveness of the electrokinetic method for porous media. In this study, five series of experiments were carried out using electrokinetic method and its combination with improved techniques. The parameters including cumulative electroosmotic flow, electrical current intensity, reservoir and soil pH variation and residual kerosene concentrations in soil were studied. The highest electrical current devoted to increased voltage and pH control tests with 48 and 94 mA respectively for a time interval of 80 to 90 hours after the start of the tests were observed. The higher electric current intensity causes faster migration of ionic species to the opposite-electrode, resulting in greater electroosmotic flow transportation. In the present study, the removal percentage of kerosene from kaolinite soil through the different electrokinetic techniques including changing the electrolyte solution (nitrate potassium and tap water), increasing the-voltage (2 volts per cm of soil), and pH control over 5 and 7 days were investigated. Results revealed, using potassium nitrate as electrolyte solution, the the removal efficiency of kerosene was 47.24% and 50%, respectively, according to the remediation time of 5 and 7 days. With an increase of 2.9 times in the electroosmotic flow over a period of 48 hours from 5 to 7 days, the removal efficiency of the kerosene increased by 2.76%. Using distilled water as electrolyte solution despite the volume of 555 milliliters of electroosmotic flow, kerosene removal efficiency decreased to 33.02% in 7 days. The percentage of kerosene removal by pH control and increased voltage up to 2 v/cm, respectively with electroosmotic flow of 372 and 452 was 47.69 and 61.43%. Hence, a higher volume of electroosmotic flow represents a greater removal of kerosene in the soil. According to the obtained results, the best removal efficiency of kerosene (inspite of higher electroosmotic flow in tests with no enhancement technique) was due to the use of electrokinetic method by combining the higher voltage enhancement technique and the use of potassium nitrate electrolyte as solution over a period of 7 days.

The development of technology along with the development of facilities for modern and comfortable life brings some disadvantages as well as environmental problems, it consists of five categories of air pollution, water, soil, heat and noise pollution. In the meantime, the issue of noise pollution in cities is a global problem in most countries, In most developing countries, they are also striving for rapid industrial development to improve the countrychr('39')s economic and social conditions. Of course, In the absence of proper control, this growth along with improving the quality of life in these countries will lead to environmental pollution, including the most important of which is noise pollution, in the absence of proper control. Noise pollution is of particular importance due to the potential for physiological and psychological effects on humans. There has been significant growth in noise pollution from man-made sources over the past 100 years, which now doubles every 10 years. Therefore, evaluation of problem and functional planning to control noise pollution and its harmful effects is an essential issue for the community. Noise pollution that is different from other types of pollution due to its source and emission characteristics. Sources of noise pollution in urban areas can be divided into two groups: Fixed sources and moving sources. Fixed sources include: industrial, construction and demolition, commercial, local and recreational. Moving resources include ground and air transportation. In urban areas, the engine and exhaust system of cars, light trucks, buses and motorcycles is an important source of noise pollution, that have major environmental impacts. Traffic noise pollution is the most important source of environmental noise pollution in cities. The main objective of the paper is to find the relationships between noise and traffic characteristics, and also to examine the impact of each one separately, so that we can find out the importance of each variable in noise pollution we will find suitable solutions to reduce the noise pollution. In this study, which was carried out at one of the important intersections of Qazvin, data including equivalent sound level, the volume of vehicles by type, traffic light timing at picked up time, distance from picked up point to intersection center, number of beeps at the time of picked up which is heard, that data was estimated at 94 points, Points were located at 10 m distance on the edge of the street and If there was an open space, points were expanded, and there were two picked up for each point .The results of modeling showed that the most important variables affecting the sound equivalent level includes the volume of vehicles, especially heavy and semi-heavy vehicles (with the impacts of 0.025, 0.125, 0.526, 0.489 for cars, motors, semi-heavy vehicles and trucks, respectively,) the green time of the approach 1 and the number horns honked in this period (with the impact of 0.05 dB per second, and .08 dB per honk, respectively), are the variables that influence the equivalent sound level at this intersection.

The pressure distribution resulting from the wave interaction in the horizontally caisson breakwater is one of the important parameters in the design of this breakwater. Due to the significant impact of this parameter, the use of composite berm breakwater has been investigated to improve the performance and reduce the forces applied to the structure .In this study, numerical modeling of pressure on composite berm breakwater and its comparison with horizontally caisson breakwater has been investigated by numerical model of FLOW-3D. In composite berm breakwater, compared with the horizontally caisson breakwater at P1 (the maximum pressure applied to the caisson at the surface of the water), the amount of achieved pressure showed the reduction of 52.09% and at P2 (maximum pressure in the caisson crest), the achieved pressure showed 63/07 % decrease. Also in P3 (maximum pressure in caisson toe), the pressure was reduced by 76.09%, and in Pu (uplift pressure under caisson), this value indicates a decrease of 53.92%.

The present paper focused on experimental and analytical study for evaluating the behavior of three-dimensional welded steel moment connection of I beam to box column under constant axial load on the column, cyclic loading in one direction and constant gravity load on the other orthogonal direction of the connection. Box columns are suitable sections for bearing loads on buildings because they have the same geometrical properties in two directions due to the symmetry around the two orthogonal axes and on the other hand they facilitate the joining of the orthogonal beams. However, due to the lack of easy access to the inside of the box sections and the need to use continuity plates or stiffeners that can perform the duty of continuity plates, the relevant solutions under different conditions and proper understanding of the behavior of connection components are still under investigation. In this research, first four specimens, including two internal and two external three-dimensional joints, are made and tested. The internal specimens consist of a cold-formed steel box column (HSS) and connected beams from four sides with the external diaphragm, and the other one with a built-up steel column and inner diaphragm. The external specimens are also the same as the internal samples include two types of inner and two types of the outer diaphragm. In all joints with the outer diaphragm, the steel cover plate connected to the column as a collar by groove welding and the web of beams by fillet welding. Then after, based on the experimental results, analytical finite element models are developed using ABAQUS software and the effect of three parameters such as the axial load of the column, the column steel plate thickness, and the thickness of cover plates on the behavior of internal joints with external diaphragm are studied analytically. Generally, experimental results of all specimens showed that the seismic behavior of samples with the external diaphragm is more close to the other one with the inner diaphragm and the failure mode followed by occurring plastic hinge in the beam precisely at the end of cover plate. However, there is a little bit different due to the experience of smaller strains than the yield limit of the panel zone in the internal joint specimen with the outer diaphragm compared to the inner diaphragm. The results extracted from the nonlinear analysis also illustrated suitable accuracy with the experimental results. Each of the parameters mentioned above could change the failure mode and ductility of the connection system‏. In other words, increasing the ratio of the axial load to the nominal capacity of the column to the value of 0.42, the failure mode transfers from beam to the column despite the growing of ratio of energy dissipation. Meanwhile, for the column bearing load ratio more than 0.58, global buckling of the column and brittle failure will happen. Moreover, by decreasing the plate thickness of the column less than 15 mm, the failure mode transfers from beam to column and the energy dissipation of the specimens reduces. Also, for cover plates, less than 20 mm thick, the mode of failure will take place in the column. However, if higher strength is used for both cover plates and plate thickness of the column, the lower thickness of the cover plate will be required in order to create the failure mechanism in the beam.

Two main goals of water diversion away from rivers are sediment control and water supply with minimum sediment. These goals are commonly accomplished by using some hydraulic structures such as: sills, spur dikes and submerged vanes. These structures make changes in the pattern of flow and consequently the bed topography that lead to control of sediment entry into an intake. Despite their important role in sediment control, the results of previously published works indicate that in some cases these structures can cause substantial scour near the bank at the downstream of the intake on the main channel that may seriously jeopardize the stability of the bank in this area. Using six layouts this report presents the results of an experimental study on the individual and combined effects of these structures (with different dimensions) on the bed topography at the upstream to downstream of main channel and the intake entrance. Furthermore, by measuring the length, width, depth and area, the scour region near the bank at the downstream of the intake on the main channel was qualitatively/quantitatively evaluated. Experiments were performed in a direct flume equipped with a recirculating sediment having a 90° lateral diversion channel at three discharge ratios of 0.12, 0.15 and 0.18 and in six sediment control systems.  The results show that both individual structures (in particular, spur dikes and submerged vanes), and their combination, have significant effects on the bed topography at the upstream/downstream of the main channel, the intake entrance, and particularly at the bank connected to the intake that thus affect the amount of sediment entry into the intake. In fact, submerged vanes, by creating a secondary flow, generate a helical motion near the bank connected to the intake causing important changes in the bed topography in an area at the intake. The spur dikes, by flow deviation to the reservoir and also increase in the flow velocity, create a general scour along the flow path from upstream to downstream of the intake on the main channel. Additionally, they, by creating fluid flow in a curved path and thus a helical motion, cause local scour around the bank connected to the intake on the main channel. The results also indicate that these structures and their combination play an important role on the size and area of the scour region near the bank at downstream of the intake on the main channel, but their response varies with discharge ratio. It was also observed that in many conditions sill causes a decrease in the size and area of the scour region at the downstream of intake. Similarly, although submerged vanes cause significant scouring at the upstream and downstream of the intake, in some conditions, they reduce the size and area of the scour region at the downstream of the intake. Last but not least, although spur dike causes a rise in the area of the scour region throughout the main channel as well as the intake entrance, its combination with sill and submerged vanes in some conditions reduces the area of the scour region at the intake downstream.

Aging in asphalt pavements results in reduced serviceability and flexibility of pavements. Aging is not commonly considered as distress, but it substantially effects the rate of evolution of various distresses. One of the common distress observed in aged asphalt pavements is cracking. If cracks/micro-cracks are healed during their initial formation, the service life of the pavement will be increased. Otherwise, there will be the risk of crack propagation that results in more cracking and loss of pavement strength. It is well known that asphalt mixes have capability of self-healing their cracks/micro-cracks when they are exposed to high temperatures. Cracks/micro-cracks in asphalt mixes can be healed through an induced healing process. Induced healing of asphalt mixes by applying external electromagnetic radiation is an innovative technique to repair cracks/micro-cracks. Applying external energy through electromagnetic radiation increases the temperature of the asphalt binder in mixes, allowing it to move and fill the cracks/micro-cracks. Flowing and crack filling of asphalt binder play a significant role in induced healing characteristics of mixes. As temperature of the asphalt binder is increased, its viscosity will be decreased drastically. When asphalt binder gets to Newtonian fluid temperature or higher, the melted binder moves inside the cracks and micro-cracks and subsequently, the cracks will be healed. The aim of this research was to evaluate the effects of different aging levels on induced heating-healing of asphalt mixes. In order to impose different aging levels, asphalt mixes were aged in oven for 3, 5, 7 and 9 days at 85 ºC. Activated carbon was added to mixes so that to enhance electromagnetic sensitivity of mixes. In addition, effects of activated carbon on mechanical properties and microwave heating rate of mixes were determined. Results indicated that activated carbon, as a powder-based additive, improves electrical conductivity, induced heating-healing rate of asphalt mixes. In addition, it was shown that aging phenomenon in asphalt mixes decreases their heating rate, which was more pronounced in higher aging level. Lower heating rate of asphalt mixes resulting in lower efficiency of induced healing of mixes. For evaluating healing capability of mixes that were subjected to different aging levels, Semicircular Bending tests (SCB) was conducted at intermediate and low temperatures. It presented that induced healing efficiency of mixes decreased as the aging level and the notch length in SCB testing were increased. The adverse effects of aging on induced healing process can be attributed to increased viscosity of the asphalt binder in mixes, which limits moving capability of melted asphalt binders to move through damages and properly heal the cracks. Moreover, it resulted that, lower heating rate of aged mixes can be considered as another reason of reduction in induced healing efficiency. The results indicated that increased notch lengths not only affects load at fracture and fracture energy of mixes, but also it plays a significant role in induced healing efficiency of mixes. For further evaluation of the healing ability of asphalt mixes, combination effects of aging, notch lengths and testing temperature parameters were also investigated. Notch length and testing temperature was found to have significant effects on induced healing efficiency of mixes. In addition, the results indicated that induced healing efficiency of low temperature cracked asphalt mixes were more than that of asphalt mixes that were cracked at intermediate temperatures. The results suggest that the necessity of considering aging level in analyzing induced heating-healing process of asphalt mixes.

The history of the human efforts for safety against earthquakes shows the catastrophic and harmful events, even nowadays. The majority of decisions in seismic safety policy are based on randomness assumption for earthquake time series. The accuracy of this assumption assessment, can accurate the strategies and resulted in more secure decisions. Also in structural control context, seismic time series prediction in the feedback systems, can reduces the time of control system reaction and in subsequent decreases structural damages. Recent studies have shown that dynamical structure of these complex time series can be better understand using nonlinear dynamics theory. In the present paper, we evaluate randomness and nonlinear characteristics of 9 earthquakes time series from metropolitan Tehran earthquake database using chaos theory conceptions. These earthquakes are Arjomand, Bumahen, Damavand, Eshtehard, Firuzkooh, Taleqan 1, Taleqan 2, Taleqan 3 and Tehran earthquake. To this end, we reconstruct phase space for delay time calculation using average mutual information function. Embedding dimension is calculated based on false nearest neighbors. Correlation dimension is used for earthquake chaotic behavior assessment and local prediction algorithm and artificial neural network are employed for earthquake prediction. Results illustrate nonrandom nature of evaluated earthquakes. These earthquakes have high dimension chaotic behavior. Earthquake prediction is good and acceptable accuracy using chaos theory and artificial neural network. The existence of the specific attractors in a part of 2D reconstructed phase space for the earthquakes show the presence of a nonlinear processes. This is an evidence for no stochastic behavior of the earthquakes. Also, reduction in the false neighbors with embedding dimension increases, shows no stochastic time series. Lyapanov exponent positive gradient displays a nondeterministic process, although it cannot warranty the chaotic behavior. Correlation exponents have high values for Taleqan1 and Tehran earthquakes. So these earthquakes saturate in large quantities. Bumahen and Damavand earthquakes correlation exponents have increasing trend and do not saturate. These observations prove the chaotic behavior of high dimension or random process with inconsiderable chaos. So these earthquakes cannot be predicted properly. Performing the local prediction based on the selected embedding dimensions and the neighbor’s number, showed that the predicted time series are relatively good for the earthquakes of Arjomand, Eshtehard, Firuzkooh, Taleqan 2 and Taleqan 3. Proper anticipated of trends, upward and downward branches as well as amplitudes illustrate the chaotic nature of the earthquakes. The correlation coefficient for Arjomand, Eshtehard, Firuzkooh, Taleqan 2 and Taleqan 3 are 0.9541, 0.4494, 0.5124, 0.6600 and 0.3697 respectively. In the case of Talegan1 and Tehran earthquakes, time series amplitudes and peaks do not predicted appropriately, but the prediction is acceptable. Correlation coefficient of Taleqan1 and Tehran are 0.2452 and 0.1760 respectively. Bumahen and Damavand earthquakes do not trace properly. It should be noted that for each earthquake, 20% of the endpoints of accelerations are used to evaluate the prediction process. According to the results of the analysis and earthquakes prediction in Tehran region, using phase reconstruction and artificial neural networks, we can say that the dynamics governing the earthquakes in this region are not random, but, chaos with high dimension. Earthquake prediction is good and acceptable accuracy using chaos theory and artificial neural network.

Pervious concrete is a concrete that, given its high porosity, allows higher rates of water infiltration through it. Although asphalt and concrete pavements have high structural and durability capabilities, they have a considerable high impact on the environment in terms of environmental as well as acoustic noise production. One of these problems are the drastic decrease in rainwater penetration to the ground and the consequent flooding disasters in the cities, which can lead to significant financial and life damage. On the other hand, surface clay pollution runoff can lead to clogging and take negative impact at effective permeability of such concrete. Thus making the most important feature of this concrete, which is high permeability, would be accompanied by some difficulties. In this study, using silica fume, it’s been tried to make a permeable concrete in order to have desirable mechanical properties, high permeability and less clogging. In addition, with the use of leca and scoria lightweight aggregates, the specific gravity of pervious concrete was significantly reduced to help noise pollution reduction by increasing internal and structural porosity. The results showed that the samples containing leca has a better performance in mechanical tests. Specimens containing scoria aggregates have higher porosity and permeability, which both have high importance in pervious concrete. Replacing 10% of cement by silica fume improved the mechanical properties of the specimens. In all cases, the samples showed acceptable permeability for slurry passage even at high concentrations, but the difference between the 10% clay suspension compared to clay-free water was significant, while the hydraulic conductivity decrease rate was much lower with increasing the concentration of clay.

In Iran, thousands of tons of plastic and rubber materials are discarded as wastes each year. The accumulation of these wastes around metropolitan areas has become a major environmental problem for cities and countries across the globe. Thus, many efforts have been made in recent years to find ways to recycle waste plastic materials and eliminate them from the environment. In this regard, reusing recycled materials is a strategy to deal with this problem. Since these waste materials do not have a proper quality to be used for usual life purposes such as household items, thus the best application for these materials is to use them as aggregates in the construction industry. Furthermore, using waste rubber materials such as scrap tires in the concrete mix is regarded as one of the efficient ways to recycle these waste materials. In addition, substituting a fraction of natural aggregates in the concrete mix by waste materials is a promising strategy to deal with environmental problems associated with these materials. Given that the presence of waste aggregate in concrete degrades its properties, adding fibers to the concrete mix has been shown to improve the mechanical performance. Therefore, in the present study, the compressive strength of the concrete reinforced with steel fibers and containing recycled scrap tire rubber aggregate was evaluated after exposure to high temperatures through an experimental program. Here, a total of nine mix designs were prepared for the experimental phase, with the test variables being the volume percentage of tire rubber aggregate as a replacement for natural sand (0, 5, and 10%), the volume fraction of steel fibers (0, 0.5, and 1%), and temperature (20, 200, 400, and 600 °C). Moreover, the compressive strength values were compared with those predicted by the ACI 216 and EN 1994-1-2 codes. The results showed that adding steel fibers together with tire rubber aggregate in the concrete mix led to a decrease in the compressive strength of the heated and unheated concrete specimens. In addition, as temperature increased, the compressive strength of all the concrete specimens saw a considerable reduction. In this regard, after exposure to 600 °C, the compressive strength loss rate was higher compared to that after exposure to other temperatures, such that the compressive strength of the reference specimen and those containing tire aggregate and fibers decreased by 59.5-76.9% relative to that of the corresponding specimens at ambient temperature. ACI 216 and EN 1994-1-2 provide a relatively good estimation for the normalized compressive strength of all the concrete specimens containing tire rubber and steel fibers at 200 and 400 °C; however, they give an overestimation for the reference concrete. In addition, the above codes give a relatively good prediction for the normalized compressive strength of the specimens exposed to 600 °C (except for specimens ST0TR10, ST0.5TR10, and ST1.0TR5). Finally, by employing the response surface method (RSM), an optimum solution was proposed for the design parameters in which the compressive strength of the fiber-reinforced concrete containing recycled tire aggregate was maximized at different temperatures.

The present paper investigates and compares the crack propagation in concrete gravity dams using two models of linear fracture mechanics and plasticity damage concrete. The first model is based on linear concrete behavior using the extended finite element method without considering the effect of strain softening on the crack tip while the second model is based on the nonlinear concrete behavior and the strain softening in tension with damage parameter. According to two different algorithms and based on two models, several benchmark examples are reviewed and the results compared with those reported in the literature. Then, path of the crack growth in Koyna gravity dam due to a seismic excitation of Koyna earthquake in 1962 has been performed by considering the dam-reservoir interaction. The results show that due to low compressive stresses during analysis of concrete gravity dams, consideration of compressive nonlinear behavior has no effect on crack initiation and almost is the same for two models. However because of crack opening and closing with tapping the crack faces together in extended finite element model, the compressive stress will be more than the allowable stress of concrete. Crack initiation at downstream and upstream face occurred at angle of 90 and zero degrees respectively, which in both models, the numerical results are in agreement with the experimental model. The crack in the extended finite element model grows faster such that the crest block of dam in this model is separated from the dam body, earlier than the concrete plastic damage model. Also the values of dam crest displacement and hydrodynamic pressure in the reservoir in extended finite element model with linear elastic fracture mechanic are more than the other model, which can be attributed to the linear and nonlinear behavior of concrete in extended finite element and concrete plastic damage model respectively. In the extended finite element model, due to using linear fracture mechanic, the maximum principal stress in the cracked elements reaches the values greater than the maximum tensile strength, but in the concrete plastic damage model as soon as the stress reaches a tension limit value, elements are damaged and the stress is reduced. In both models, the crack located at the slope change area, propagates with the downward slope from downstream dam face and connects to the crack at upstream face which is growth horizontally. Because of laboratory sample dimension and boundary condition of dam-reservoir compared with actual manner, neither of two crack profiles covered the experimental model, accurately. But it is shown that the crack profiles in the extended finite element model are more consistent with experimental results. Finally, the results show that the crack profile are slightly different in the two models because of quasi brittle behavior of the dam concrete, which can be attributed to the small fracture process zone of the crack tip in comparison with the dimension of the concrete gravity dams such that by removing strain softness part, the error in the amount of additional computation can be neglected.

Concerns for climate change, reduction of greenhouse gas emission and environmental pollution, besides economically dependency on fossil fuels and political aspect motivate governments and policy makers to take into account replacing usual vehicle with alternative fuel vehicles (AFVs) such as Compressed Natural Gas Vehicles (CNGV) and Gasoline-Electric Hybrid Vehicles (GEHV). The air pollution in Tehran is a serious concern that based on this problem, CNGV has been introduced to Iranian market from 10 years ago. On the other hand, with the approval and notification of the removal of the electric vehicle importation’s tariff law, GEHV has been entered into the market of Iran as a new entrant. The purposes of this paper is to identify the effective factors to choose AFVs for drivers in Tehran and the assessment of effects of the incentive policies that increase AFV shares and computing their willingness to pay (WTP) for AFV under different incentives. This study designed a questionnaire which includes 3 parts: current vehicle features, dominant travel characteristics, socio-economic properties and the prioritization of effective factors on new vehicle purchase, and the tendency of AFVs choice with different scenarios representing different features. A random sample of 365 respondents was interviewed in a face-to-face survey in February 2016 in the technical inspection centers and in compressed natural gas stations. Finally, for the determination of effective factors on current and new vehicle purchase with revealed preference information and the assessment of AFVs usage tendency with stated preference information, the Multinomial Logit models have been used and WTPs are calculated. The incentive policy in Tehran, like previous studied countries, was the most influential factor in motivating consumers to buy AFVs in comparison to improvement of AFV specifications. The results show that drivers’ WTP is 5 MT for free access to even-odd area for CNGV and 12 MT for GEHV, also WTP for free access to pricing area in Tehran central business district is equal to 10 MT for CNGV; i.e. people tend to pay this extra cost for AFVs to access to pricing areas. These values are comparable with similar studies in cities located in developed countries. However, the results of this study show that WTP for fuel cost in Iran is considerably less than WTP of people driving in developed countries. The fuel cost and access time to gas stations are influential variables on CNGV choice. The vehicle acceleration and driving range are influential variables on GEHV choice.