AMIRKABIR JOURNAL OF CIVIL ENGINEERING
Year:2020 | Volume:52 | Issue:6|Papers Count:15

Evaluating the groundwater level in arid and semi-arid regions of the country requires accurate prediction and efficiency of its fluctuations. The use of modern methods, including evolutionary algorithms, artificial neural networks and fuzzy methods, is very useful for prediction the groundwater level and generating artificial water surface data due to its high efficiency. In this research, by using Election and Imperialist Competitive Algorithms, artificial neural network, monthly data for 9 years as well as groundwater level of 10 wells, predicted the 7-year the groundwater level of Reshtkhar plain in khorasan-Razavi. In order to train the models, the statistic data was provided on 10 observation wells with a 9-year (2002-2014), which 70% of the data was introduced as training data to the model and 30% of the data was used as a test for calibration of the model. The results of the Election Algorithm predicted Reshtkhar groundwater level for the year 1400, between 14 to 16. 5 meters in diffirent areas of the plain. Based on the calculations and the results obtained from the statistical parameters, the Election algorithm was RMSE, R2 and NSE, 0. 029, 0. 90 and 0. 73 respectively, compared with the two methods of artificial neural network and Imperialist Competitive Algorithm has a significant ability to predicte the groundwater level.

Compact clay layers are one the most impermeable layers. Dispersivity and cracking of clay layers are among the factors that reduce the efficiency of clay and necessitate clay stabilization. Clay healing properties and the importance of self-healing cracks in clay layers as one of the characteristics and attributes of clay in recent years have been studied. In this research, the self-healing performance of clay layers due to the addition of lime to the clay materials of Gordyan dam borrow pit (Gargar) was investigated. For this purpose, two dispersive (S2 and S3) soil samples (ND3 and ND4) were investigated by adding lime to the extent 0. 25, 0. 5, 1 and 2%, and Double Hydrometer, Atterberg limits and Pinhole tests of dispersivity and self-healing were investigated. The results showed that by adding 1% of lime to clay, the range of plasticity index increased and the discharge rate of the pinhole test for both samples was 28% and the final diameter of the sample for both samples decreased by 67%, indicating an improvement in self-healing process and a reduction of dispersivity and becoming non-dispersive soil (ND1). The results also showed that pinhole testing has reliable and more accurate results than other tests in determining soil dispersivity.

Today, the use of waste tires has been expanded in various geotechnical projects to absorb and reduce the vibration caused by seismic and dynamic loads, and therefore it is important to study the effect of different parameters on their behavior and dynamic characteristics in combination with soil. So this study examined the effects of loading frequency on dynamic properties of sand-tire powder mixtures such as shear modulus (G) and damping ratio (D). A series of 1-g shaking table tests were performed on sand-tire powder mixture. Tire powders were added to the sand with 5%, 10%, 15% and 20% in gravimetric basis and with a relative density of zero were subjected to sinusoidal loading at frequencies of 0. 5, 1, 2, 3, 5, 7 and 9 Hz and at input acceleration of 0. 1g and 0. 3g. The results showed that in all cases, the increase in frequency in the same cycles increased the shear modulus and the damping ratio. Also, with increasing shear strain, the shear modulus of the mixture decreased, but the damping ratio increased. On the other hand, by increasing the tire powder, the value of the shear modulus is reduced, but the amount of damping ratio is increased.

Due to the advantages of Concrete Filled Tube (CFT), attention to them is increasingly on the rise. In spite of the extensive research done in these sections, in some cases, as in the case of less frequent sections or using different types of concrete, the need for research to complete the design rules and guidelines seems necessary. The present study was conducted with an experimental approach to the study of CFT under Eccentric load. In this study, 8 CFT columns with a hexagonal cross section of 150 cm in length were tested. Concrete used as the core of the samples was plain and fiber concrete. The displacements in two directions been recorded and the force-displacement diagram for all samples has been drawn. Parameters such as bearing capacity, ductility index, energy dissipation and effective hardness have been analyzed and compared. Based on the comparison of the results, it was found that in columns that are only under axial load, the increase in concrete core strength significantly increases the bearing capacity of the specimens, so that an increase of about 50% of the concrete core strength causes an increase of about 20% of the loaded capacity of the specimen,However, by increasing the bending moment, the effect of concrete core resistance is greatly reduced. Also it was found that specimens filled with fiber concrete have greater ability to maintain effective hardness. It also seems that the presence of fibers in concrete affects the ductility and energy dissipation parameters.

One of the environmental problems of wastewater is the presence of micro and macro nutrients, the most important of which is phosphorus and nitrate. Hence, in this study removal of phosphate and nitrate from aqueous solution was conducted using electrocoagulation (EC) processes with Al electrodes. In the present study, an electrocoagulation reactor was used in a laboratory scale with a volume of approximately 1200 ml equipped with 3 Al-electrode in a size of 5 × 12 cm to remove phosphate and nitrate. The effects of operating parameters such as applied voltage, initial pH of the solution, value of FeCl2 and reaction times were evaluated. The effect of pH and FeCl2 parameters in inlet and facultative ponds were also studied. Also, pH changes in the oxidation process were investigated. Finally, it can be said that phosphate was completely eliminated in facultative and outflow ponds, but due to the low initial concentration of phosphate in the outlet, less voltage (10 V), less time (about 3 minutes), low FeCl2 dosage (0. 2 mg/l) and original pH of the solution were applied compared to the facultative pond., 100 % of nitrate in optimum condition (pH =5. 5, applied voltage = 25 V, FeCl2 = 0. 65 mg/l, time = 11. 50 min) in output pond has been removed. In EC process the electrocoagulation process using aluminum electrode, as well as it's relatively low cost and simplicity, has a good effect on phosphorus and nitrate removal compared to other methods.

The spatial analysis of accidents occurring in Highway with the aim of identifying theeffective parameters on the increase in the severity of accidents can be effective in decision making by professionals and decision makers to improve road safety in order to reduce the severity of road accidents. The purpose of this study is to provide a method for analyzing the severity of crashes and determining its effective factors in the freeways based on the spatial clustering functions and the data mining model of the regression tree. The proposedmethodis evaluated and tested on the Qazvin-Loshan freeway. In order to investigate the spatialdistributionofcrashes inthe axis of the study during the period of from2011to2016, the Geographic Information System’, s spatial functions such as Getis-OrdG*Autocorrelation andkernel density functions have been Used. The preliminary results of spatial analysis showed that the focus of accidents in horizontal curves was greater. According to this achievement, in the next phase of the study, in order to study the factors affecting the severity of accidents, the Classification andRegressionTree was used on accidents occurringinthewholeaxisandspecifically in thehorizontal curveswith highcrashes. Thestudy of the relative importance of other variables in the proposed model shows that the geometric design, type of crashes and day of theaccident are the effective factors in increasing the accident severity at the Qazvin-Loshan Freeway. Inaddition, the results of modeling on horizontal curves crashes showed that the accident location, especiallytheshoulder, as well as the time of the accident, cause serious accidents. The results showedthattheintegrationofGISspatialfunctions withnon-parametricdecision-making tree-based datamining analysis, which is capable ofsimultaneous modelingofquantitativeandqualitativedata, is used to determine the factors affecting theseverityofaccidents andtospatial analyzethe patternsofaccidents usedinsuburbanarea, iseffective.

Collapse refers to sudden decrease in the soil volume upon wetting which is attributed to loss in the strength of the inter-particle bonds. Collapsible soils can be founded at vast areas around the word and subtropical areas of Iran. Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils. For this reason, collapse behavior of loess soils has been subject of interest. In this study, stabilization of Semnan loess which is composed of fine sand and silt bonded by weak clay bonds has been investigated. The loess was mixed with Portland cement in the order of 0. 5%, 1%, and 2. 5% for and with nano-clay in order of 0. 05%, 0. 1%, and 0. 25%. The specimens were prepared to achieve dry density of 14 kN/m3 and water content of 5%. Oedeometer tests were performed to determine the collapse potential according to ASTM D5333 after 7, 14, and 28 days. Results showed that both Portland cement and nano-clay can reduce collapse potential. Improvement performance was significantly dependent on the binder content and curing time. The best improvement performance was observed at low nano-clay content and it was reduced by increasing nano-clay content. Unlike the cement stabilization, treatment process with nano-clay was relatively fast that terminated when soil moisture content was evaporated. In addition, in this study micromechanical soil behaviors were investigated by scanning electron microscopy (SEM) image of the treated and untreated specimens.

Flood flow in rivers is often of density current type. Hence, recognizing and exploring these currents can solve some problems of sedimentation. In this study, the effect of porosity and the angle of permeable obstacles on the control and trapping of density current have been investigated in the laboratory. For this purpose, an expanded polystyrene (EPS) polymer was used with 1. 135 g/L density and average diameter of 1. 15 mm. The experiments were carried out with two concentrations (10 and 20%) and 5 porosity and 4 angles. The obstacles were made of palsy glass plates and two types of groove and cavity with 8. 2 mm width of the groove and the diameter of the cavity. The results showed that, with an increase in porosity ratio, the amount of trapping to optimum porosity decreases and then increases. The optimal porosity of the cavity and groove is 22 % and 19%, respectively. In experiments, the cavity trapping was observed more than the groove, in the concentrations of 10. 20% it was 0. 13 and 0. 14%, respectively. In addition, with the increase of the angle, the amount of trapping has reduced and its value was observed in the groove more than the cavity. The correlation coefficient in the grooves and cavities was 0. 996 and 0. 937, respectively. The major effect of obstacles, reducing velocity and slowing flow were identified as the average velocity in the cavity was 62. 3% higher than the groove. Accordingly, in the same conditions, the cavity obstacles have better performance than the groove obstacles.

The effects of surface dissolution by oxalic acid were investigated on the flotation kinetics and kinetics of collector adsorption in ilmenite flotation in the presence of olivine-pyroxene, tremolite-clinochlore and quartz. Fitting of first order kinetic model on the results of flotation before and after surface dissolution showed that flotation kinetic constant (K) and ultimate recovery (R∞, ) of ilmenite is increased after surface dissolution and they are decreased for gangue minerals. The results showed that kinetic selectivity index of ilmenite in the presence of olivine-pyroxene, tremolite-clinochlore and quartz are increased from 1. 28 to 1. 98, 1. 42 to 3. 02 and 3. 58, respectively, after surface dissolution indicating the positive effect of surface dissolution process. Investigating the kinetics of collector adsorption showed that the collector adsorption is conforming to second order kinetic model. After surface dissolution, the kinetics of collector adsorption and initial rate of collector adsorption on ilmenite surface is increased from 3. 85 to 8. 44 g. mol-1 min-1 and it is decreased for olivine-pyroxene, tremolite-clinochlore and quartz from 6. 33 to 5. 03, 7. 3 to 6. 22 and 7. 77 to 7. 37 g. mol-1 min-1, respectively. These results are in good agreements with the results of collector adsorption via UV analysis which the collector adsorption on ilmenite surface is increased and it is decreased for gangue minerals after surface dissolution. The results of SEM showed that the surface of ilmenite becomes smoother and uniform and about the gangue minerals, some cavities are produced due to dissolution of surface cations.

Rockbolts are one the best systems to stabilize plane failure of rock slopes. The passive bolts are loaded and activated when rock block slides while pre-tensioned types are initially loaded prior to any rock sliding. The pre-tensioned rock bolts make the rock layers pressed together and the friction between them is activated before slipping, and probably no displacement between the layers is occured. If a slippage occurs after the installation of a pre-tensioned rock-bolt, an excessive load is applied. In this paper, the bolt contribution generated by the pre-tensioned and passive rock-bolt in discontinuity is analytically simulated, and the effect of roughness angle, inclination of the bolt to the joint plane, pre-tensioned force, and strength of the rock are evaluated. For modeling, it is assumed the sliding imposes a bending moment to the rockbolt, which leads two plastic hinges to be created. The part of bolt between two hinges (located in either sides of the joint) is considered a beam with two cantilever supports, which is loaded by a uniform distribution generated by surrounding grout/ rock. The results show the pre-tensioned rock-bolts are effective when the resistance of the rock or grout around the bolt is high.

Studies conducted on Steel Plate Shear Walls (SPSWs) performances indicate high stiffness, capacity, ductility and significant potential of energy absorption of this lateral seismic system. In this regard, using SPSWs in Reinforced Concrete (RC) constructions has recently been considered by researchers. In this paper, two different connection types have been proposed and numerically investigated to connect SPSW to RC frame (RCF). In the first type connection, SPSW has been embedded in RCF by a few studs through fish plates. However, in the second type it has been connected to RCF by additional stirrups through, which has been welded to the endplate. The behavior of connections has been evaluated using non-linear finite element analysis (NLFEA). Parametric study has been conducted on the thickness of SPSWs and the way of studs and stirrups placement in the length of columns. Results of the specimens with different types of connections demonstrated that using both connection types lead to prominent increase in stiffness and capacity comparing to the reference RCF. Investigating the studs and stirrups placement showed that there is no need to use studs and stirrups in whole column height. Similar results can be obtained by connection in a length of 0. 3 or 0. 2 of the column free height. Dual system behavior factor of special RC frame with SPSW was estimated to be 8.

Ring footings have been used in various industries like oil and gas. So this kind of footings is very important and doing some works to improve their behavior, can be very important. In the present study, by using experimental tests, the behavior of ring footings with a constant outer diameter of 300 mm based on reinforced bed with granular rubber particles alone and also in combination with a geogrid layer, subjected to static loads, has been investigated. The results showed in both unreinforced and rubber-reinforced bed, the ring footing with inner to outer diameter ratio of 0. 4 had the maximum bearing capacity. Also the optimum thickness of rubber-reinforced layer is equal to 0. 5 times the outer diameter of ring footing,in this case the bearing capacity can be increased by 41. 5% compared with the unreinforced bed,more increases than optimum value, have reverse results and lead to decrease in bearing capacity and increase in settlement. Using geogrid layer can activate reinforcing effects of rubber-reinforced layer with high thicknesses, but its value is not big enough to overcome the negative effects of using rubber-reinforced layers with higher thicknesses than optimum value. At last, using geogrid reinforcement in combination with rubber particles can be more effective than using each of them alone. In geogrid-rubber reinforced bed, the bearing capacity can be increased by 62. 7% compared with the unreinforced bed.

Shear keys are bridge components that support the superstructure in transverse direction and may experience large displacements and extensive damages during earthquakes. Shear keys are designed to limit damage to abutment walls and piles by restraining the transverse movements. The shear force transferred to the abutments is controlled by the design and detailing of the shear keys. Damage to shear keys during earthquakes may affect significantly on seismic behavior of the abutments and consequently the bridge system. In this paper, a damage index is proposed for damage assessment of the bridge shear keys. The proposed damage index is defined based on the friction behavior and the ratio of the energy dissipation capacity to input energy. To evaluate the reliability of the damage index in damage assessment of the shear keys, finite element models of shear keys units, previously tested under cyclic loadings are developed and the proposed damage index is calculated. In addition, seismic response of shear key specimens are obtained under seven earthquake records using incremental dynamic analysis and the damage index is calculated for the shear keys in different PGA values of earthquakes. The results indicate that the proposed damage index can predict the damage progression in shear keys throughout loading histories and can provide reliable values for damage levels of shear keys with respect to the experiment observations.

The influence of the strength reduction factor due to nonlinear behavior (Rμ, ) on the lateral strength of Single-Degree-Of-Freedom (SDOF) structures causes to limit the displacement ductility demand to the predetermined maximum tolerable ductility. In addition, Rμ,is used for determining the behavior factor in Multi-Degree-Of-Freedom (MDOF) structures. Following this, in this paper, Rμ,and the inelastic displacement ratio (CR) for equivalent SDOF systems under strike-parallel (NF-SP) and strike-normal (NF-SN) components of near-field ground motion, and also far-field (FF) ground motion were assessed. Furthermore, CR obtained by this study was compared with C1 proposed by FEMA440. The deflection amplification factor-to-behavior factor ratio (Cd/Ru) for different ductility levels was computed. After evaluating nonlinear effects of SDOF structures based on Rμ,factors, these factors for MDOF structure were modified considering higher mode effects, and a simplified practical expression was proposed to estimate the base shear modification factor. The results indicated that Rμ, , corresponds to near and far-field ground motions can be different. In addition, CR does not depend on type of earthquake, and it converges to 1 by increasing the period of vibration. In addition, modification factor can be increased with period and ductility demand.

Prestressed cylindrical tanks are commonly utilized to store the large volume of water or other various fluids. The prestressed water tanks are used as a part of the fire-fighting system or water refinery process. In this article, the seismic responses of the prestressed concrete cylindrical tanks are investigated under earthquake inputs. A series of dynamic-explicit analyses are performed to study water sloshing phenomena effects on the prestressed concrete tank behavior using ABAQUS software. A shaking table test program is conducted to validate the numerical analysis. A cylindrical prestressed concrete tank was constructed and subjected to several seismic records. In addition, the numerical analysis capability to simulate the sloshing waves is verified using other research results. Several numerical models are prepared with different radius to water height ratios (R/H). The recorded El-Centro and Tabas accelerations are employed as seismic excitations in the numerical models. Comparisons of the experimental and numerical results demonstrate a reasonable agreement between them. The numerical analysis results demonstrates that the Arbitrary Eulerian-Lagrangian analysis method has a considerable capability to simulate the water sloshing. The seismic excitation effect on the tendons prestress loss is negligible in the investigated numerical models.