AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2018 | Volume:49 | Issue:4 |Papers Count:21

Evaluation of a river self-purification capacity provides required information for a sustainable management of the river receiving pollutants. The main target of this paper is to study and predict the seasonal variation of self-purification capacity of Karun River, IRAN. Dissolved oxygen (DO), BOD, nitrate and pathogens were the main quality parameters, which were considered in this paper. To achieve this aim, a length of 113 km of the river was simulated using QUAL2Kw model and calibrated and verified using field measured data in 2010. The above mentioned datasets were used also to determine the critical periods of self-purification phenomenon, involving the model for BOD, nitrate and pathogen parameters. Furthermore, three scenarios were supposed and considered, including, 30% reduction in the waste waters flow, increasing the river monthly flow by 30% and finally decrement of the waste waters concentrations by 30%. The above mentioned scenarios were assumed in order to enhance the water quality of the river, during the months with no standard limits. Results indicated that, the decrease of nitrate in January and February and the decrease of BOD for all month except October up to 30 %, have had the most positive effects on river water quality. The 30% decrease of waste waters flow rate containing pathogens had the most positive effects on the river water quality.

One of the most important applications of geotextiles is as drainage and filtration adjacent soil in civil engineering projects. The using of this material has several benefits such as such as permeability and filtration that effect of these benefits, theoretical or experimental, have been evaluated by researchers. One of the important issues is the effect of contact pressure on permeability of geotextile-soil systems which has been less investigated. In this paper, the impact of overhead pressure on permeability of the soil in the vicinity of nonwoven geotextiles in a drainage system has been investigated by experimental tests. For this purpose, a special measuring cell was designed and built in soil and geotextile system which the hydraulic properties were evaluated in variation of pressure. The results showed that the variation of system permeability is non-linear in variation of overhead pressure. Also the thickness of geotextile has important effect on the permeability in a soil-geotextile system.

In mineral industries, most of the processes are carried out in an aqueous environment. With the purpose of reducing costs and environmental impacts،the water content of tailing stream should be recovered. Thickening is the most widespread method of water recycling process in mineral industries. In this work, the effect of solids concentration, flocculant dosage and particle size on settling flux and compressibility of copper processing tailings were investigated. Samples were collected from tailings of Shahrebabak copper complex and laboratory tests were conducted. In laboratory scale, settling flux and final height of suspension were examined using batch settling tests. In addition, thickener underflow solids concentration was considered as an indicator of the effect of variables in full scale. Results indicated that not only settling flux but also compressibility of the suspension was improved by reducing suspension solids concentration. Furthermore, it was found that increasing flocculant dosage from 15 to 45 g/t led to an increase in settling flux about 7 times. Moreover, both settling flux and compressibility were reduced with fine particles. Industrial scale studies showed that, increasing -75 mm fraction in thickener feed from 47 to 59 % led to a decrease in underflow solids concentration from 63 to 55 %.

Seismic performance of a cruciform rotational friction damper has been evaluated in this article. Horizontal and vertical arms’ length and sliding threshold moment are three adjusting parameters of this device which shall be optimized to assure the damper efficiency. It has been shown that the energy dissipation rate increases for shorter arms due to more relative rotation between frictional contacting surfaces. The best dimensions for friction device arms have been evaluated in this study. A simple method has also been suggested based on static analysis and aiming to find the optimum sliding threshold moment for friction damper implemented at different stories. Closed form solutions of kinetic and kinematic equations of the damper dynamic have been employed on this regard. Dissipaters’ seismic performance indexes have been evaluated through nonlinear dynamic analyses to validate the reliability of the proposed method. It has been shown that the variant values of sliding threshold moment for optimum FD at different stories improves the seismic performance index in comparison with the case of identical devices utilized on all stories. Implementation of identical friction device on all stories may cause inactiveness of the dissipaters on upper stories where the inter-story shear force is not high enough and it acts as ordinary X bracings. The proposed method provides a simple and efficient approach for FD optimum design on different stories of building without multitude of time consuming nonlinear dynamic analyses. According to the dynamic analyses results inconstant optimally designed FDs will be active on all stories while identical FDs may not be sliding at upper stories during the earthquake. Performance of optimally designed FDs has been evaluated for 4, 8 and 12 story buildings under low, medium and high intensity earthquakes. It has been concluded that the proposed dissipater is more effective for high rise buildings and its efficiency increases for severe earthquakes. Although FD utilization on X-braces increases the inter-story drifts; base shear and residual energy considerably decrease. At last it results in 5%-20% improvement in seismic performance index. 3%-6% more reduction in SPI can be achieved using different sliding threshold moments for dampers on each story.

In this study based on conducting several non-linear dynamic time history analyses subjected to the both types of near and far field three components earthquake records, the seismic response parameters of inelastic behavior of tall buildings with belt truss frameworks have been investigated. A three-dimensional basic outrigger braced tube model as well as three other resistant skeletons which contain different configurations of belt trusses in height, have been designed according to the Iranian seismic code 2800 (4th edition) and Iranian national building code (steel structures-division 10). The dynamic response parameters of all studied structures have been assessed under influence of free field three components earthquake records. Because the overall dynamic response of the studied structures would change subjected to record by record separately, the corresponding response velocity spectra of each of the selected records were notified numerically. Furthermore, in order to denote the effects of higher modes, the aforementioned response velocity spectra were evaluated corresponding to the natural period of the studied structures. Having accurate evaluation of the analytical results indicate that the existence of belt truss causes a significant increase in structural stiffness and mitigates drift and base bending moment. Also the highest drift demand obtained for the model without belt truss and the model with belt truss located at 0.5H, occurs relatively in 0.83 to 0.9 of normalized height. This demand parameter calculated for the model with the top belt truss occurs in 0.5 to 0.8 of normalized height.

Ion flotation includes removing of ions from solution by adding chemical reagents such as collectors in the presence of air bubbles. In this study, removal of Zn (II) cations was studied from low concentration synthetic wastewater by ion flotation. Sodium dodecyl sulfate (SDS) and ethylhexadecyldimethylammonium bromide (EHDABr) were used as collectors and methyl isobutyl carbonyl (MIBC) and Dowfroth250 as frothers. To investigate the effective parameters, the experimental design was performed supporting by DX7 software. Two-level factorial method was used. Sixteen experiments including 6-level variables were designed. The tests were conducted in Hallimond tube. The results showed that the optimal conditions for the removal of Zn (II) ions were: pH=3, SDS= 300 ppm, Dowfroth 250= 90 ppm and air flow rate= 1.8 ml/min. Optimal results were evaluated in a mechanical flotation cell. In optimal condition, recovery of Zn (II) ions and water were more than 92% and 8.65% after 10 min, respectively. This study showed that the use of ion flotation is a very effective method for Zn(II) ions removal from industrial wastewaters.

Most existing structures are vulnerable to the blast wave loads and therefore their resistance to such loads should be evaluated. In this study, the behavior of RC slabs under blast loading was investigated numerically. Numerical analysis can reduce the number of required expensive experimental blast tests. The variable parameters for study include: thickness, reinforcement ratio and spacing, support conditions, dimensions of slabs and location and amount of explosives. Numerical modeling was performed by the use of LS-DYNA software. It is capable of modeling the explosion and also has a wide range of material models.The results showed that the slabs were completely destructed under near explosion mainly because of punching shear. Under medium distance explosion, no complete destruction was observed. The deflection and the extent of cracking depended on the thickness and reinforcement ratio and somewhat on reinforcement spacing. The slab thickness and support condition had also a significant impact on the behavior of slabs. Interestingly, the cracking level of RC slabs did not change significantly by increasing span length.

Structural walls are widely used in building structures as the major structural members to provide substantial lateral strength, stiffness and the inelastic deformation capacity needed to withstand earthquake ground motions. In this article the behavior of composite shear walls with continuous boundary elements are compared and contrasted with a state in which the wall’s boundary elements are discontinuous and interrupted and the boundary steel columns are connected to the foundation through the column’s baseplate and bolts; and these are all to assess and appraise some hypotheses by the structural designers in designing these walls. The finite element software is first calibrated and the accuracy of its results is validated through modeling the experimental samples. In this research, the concrete’s nonlinear finite element analysis method and concrete damage plasticity model have been used for the concrete’s behavior modeling. The results of this study indicate that the wall boundary elements’ continuity improve the composite shear walls’ behavior. Meanwhile, this effect increases by an increase in the number of the wall’s floors.

Blast can cause progressive damage or complete damage in structures. Designing the structures for blast is so expensive and infeasible; hence, it is better to use the dampers for increasing the structure explosive resistance. The purpose of this research is to evaluate the behavior of steel frames equipped with steel accordion dampers under blast loading. Two types of frames, one with damper and one without that, have been studied to evaluate the effect of damper. The studied steel frames have been considered as single span with different heights (1 and 4 stories) impacted by two types of blast load with different values. For this purpose, non-linear dynamic analysis on different frames was conducted using ABAQUS software. The study showed that utilizing thin-wall accordion dampers remarkably improves the overall displacement of the frame, especially during intense blasts. The maximum reduction in displacement of 1-story frame for the top of column at the side close to blast under explosive load of 36 kg/cm2 is about 98% and the reduction is 21% for the middle of this column. For the four-story frame, the most displacement reduction about 64% was obtained at the forth story level and the reduction reaches 55% at the third story.

Currently, the framed-tube and outrigger-braced systems are known as two conventional load bearing systems in tall buildings. These structural systems can be used in tall buildings with high efficiency to provide the necessary lateral stiffness and strength against lateral forces due to earthquakes or strong storms. On the other hand, increasing the stiffness of these structures augments the relative importance of flexibility of the underlying soil and the resulting added displacements. This paper aims to study the seismic behavior of framed-tube and outrigger-braced tall buildings on flexible soil in comparison to a rigid base. For this purpose, a range of 10 to 50-storey steel buildings with both structural systems on flexible and rigid bases are analyzed dynamically and the maximum base shear and lateral roof displacement are calculated. Also for comparing the benefit of each system, the total weight of steel used per system in each case is calculated. Results indicated that the design spectrum of Standard 2800 overestimates the response of the studied systems. Overall, the tubular system more economically provides the necessary stiffness and strength of the building system.

In this study, horizontally curved steel I-girder bridges having various radii of curvatures in practical dimensions, and designed via the AASHTO standards are modeled and analyzed via the finite element software ABAQUS. The aim of these material-geometric non-linear analyses are to characterize the shear behavior, the shear failure mechanism and the shear resistance of steel I-girders in the complete bridge systems and in their equivalent single girders. Results demonstrated that the shear behavior, the ultimate shear resistance, the shear buckling resistance of single-girders and bridge system are similar; whereas the initial stiffness of the two approaches differ. Furthermore, the equivalent single-girders are incapable of predicting the correct mechanism of the shear failure in some interior panels of the bridge system; due to the negligencs of the true horizontal and vertical stiffness of cross-frames, and also due to the interaction of girders. In addition, it is shown that under a specified geometric imperfection pattern, the ultimate shear resistance of curved I-girders is insensitive to the imperfection magnitudes; whereas, the ultimate shear resistance of straight I-girders reduces with the increase of imperfection magnitudes. The AASHTO provisions however, do not require the consideration of geometric imperfections on the ultimate shear resistance of I-girders.

Shape Memory Alloys (SMA) are a kind of smart materials that their unique mechanical and thermal performances such as the ability to return to its original shape (Shape Memory Effect) and the ability to recover large strain (Super Elasticity), caused their wide application in various industries such as civil engineering. Due to the superplastic behavior of theses alloys, undergoing cycles of loading and unloading, results very little residual strain, even after exceeding the yield strain. This property causes recover forces in the structure so that they can close the cracks in the tensile zone of RC members and therefore, it is significant for structural members located in earthquake zones. In this paper the F.E modeling of reinforced concrete (RC) beams utilizing of shape memory alloys is produced and results of different loads response of modeling is verified with the available experimental results. For this purpose, firstly the finite element model of three RC beams by adding Nitinol wires in the tensile zone was made by ANSYS software. Then the beams were subjected to cyclic loading and their hysteresis curves were compared with the similar available experimental beams. The numerical results revealed, utilization of Nitinol wires in tensile zone of the beams resulted, increase in both loading capacity and ductility and decrease in residual displacement.

Recently, increasing attention has been paid to reliability based design methods due to its ability to consider different uncertainties associated with demand and capacity. Recent studies show that presence of unaccounted uncertainty may inflict unacceptable bias to computation of reliability index.Exact computations of global reliability index for multi-member structures are only possible through simulation methods. Therefore, researchers have proposed numerous methods using simplified assumption for reliability index calculation. Each method is different in the simplicity and accuracy it offers. For this purpose, in assessment of the effect of different uncertainty different methods of record selection for IDA analysis, probabilistic distribution of demand data and demand-capacity relation assumptions were used in this study to compute reliability index for “Operational”, “Immediate Occupancy”, “Life Safety” and “Collapse Prevention” limit states. The results showed that considering epistemic uncertainty in record selection and probabilistic distribution dramatically affects the reliability index and thus should be considered in future analyses.

In this research, damage reduction of structures is studied using semi-active control of MR dampers. Fuzzy control is an intelligent control method in contrast to classical control with some specific capabilities such as handling non-linear and complex systems, adaptability and robustness to errors and uncertainties. However, due to lack of learning ability of fuzzy controller, it is used in combination with a genetic algorithm, which in turn suffers from some problems like premature convergence around an incorrect target. Therefore, in this research, the introduction of the cooperative coevolution fuzzy controller in which the parameters of membership functions and rules will be searched in two separate species. To investigate and compare the performance of this controller with some other controllers, these methods are implemented on a three story benchmark nonlinear structure. The results showed that the performance of the cooperative coevolution fuzzy controller is better than the other controllers and can reduce the average damage of the structure up to %79.

Density, as a one of the important factors affecting the performance of asphalt mixture has a significant impact on the pavement serviceability. Numerous studies on computed tomography (CT) scan images of asphalt mixtures are done; however, due to the ambiguous nature at the edge of aggregates, the processing of images contains uncertainty. Static and dynamic thresholding techniques that have been conducted by previous studies were also unable to resolve and handle the ambiguity. The aim of this study is enhance the results using a new fuzzy thresholding model for separation of components and analyze the density of asphalt mixture. The analysis indicates that fuzzy threshold provides more accurate results. It was also found that, the density of asphalt mixture were determined with less than 2% error.

Nowadays, the tunnels based on the public’s needs may be built in unfavorable geological conditions. In most of these situations, the use of mechanized excavation technology is unavoidable to improve the performance and safety. Mechanized tunneling in difficult conditions with many risks, including the fault zones, water inflow and squeezing that tunneling operations could stop for a long time. It is very important to predict and assess the hazards because of the large volume of investment in such projects. In this study, it was tried to investigate the stability and convergence of environment and water inflow in seven section of the second part of the Emamzadeh Hashem (AS) tunnel using analytical and numerical methods after identification of the geological characteristics and geotechnical risks. Then, the most risky section was investigated and introduced using Fuzzy Delphi Analytical Hierarchy Process (FDAHP) and PROMETHEE methods. Thus, after selecting criteria, including the instability of the tunnel, water inflow and squeezing, the weighting of each criterion was determined using FDAHP method according to the severity, rate and probability of disaster. Finally, the most risky section of the second part of Emamzadeh Hashem (AS) tunnel was evaluated using the PROMETHEE method. Thus the H-3 section was introduced and selected as the most risky section based on geotechnical properties. The results of this study showed that a combination of multiple criteria decision making, analytical, numerical and fuzzy methods can be used to predict and evaluate the geotechnical risks and doing disaster risk reducing actions to reduce the risk.

Behavior prediction of oil well during drilling is important to prevent of instability problems and lots of cost spending. One of the problems can be pointed is failure of oil well wall during drilling. Thick-walled hollow cylindrical specimens can be able to modelling failure of oil well wall during drilling. Different triaxial cells exist for this test in world. Cell was used is designed based on Hoek cell. The benefits of this cell are ability of oil well during drilling and hydraulic fracture modelling. Also it is possible to measure the tangential strain in the center hole. This feature simultaneously is absent in most triaxial cells. To evaluate the performance of this cell, gypsum and concrete hollow cylinder specimens were made to modelling of oil wells during drilling. Literature studies and experimental results showed that, depending on the magnitudes of the applied internal pressure, external pressure and axial load, any of the radial, tangential and axial stresses induced in the cylinder considered as minor, intermediate or major principal stress. Hence, in this paper, two different stress conditions were used that consist: ϭϴ=ϭ1˃ϭr=ϭ2˃ϭz=ϭ3،.ϭϴ=ϭ1˃ϭz=ϭ2˃ϭr=ϭ3=0. Results showed that, in condition that tangential stress induced of lateral stress is maximum stress, shear failure occurred toward at around well. So, failure of wall of thick wall hollow cylinder is caused by the deviator stresses between lateral stress and inner pressure. By increasing deviator stresses, the plastic zone will increase around wall of thick walled hollow cylinder specimens. It is noteworthy that, presence of internal pressure reduces the breakouts propagation.

A leakage from oil storage tanks result in pollution of a large amount of soil by gasoil. Physical and chemical reactions between soil and the contaminant lead to a change in the geotechnical soil behavior. If it yields a negative effect, the strength of the soil may decrease and the stability of the storage tanks may weaken and resulting in the seeping of a large amount of the contaminant in the soil and groundwater. In concern with lack of information about precise leakage of oil, the precise level of pollution and changes in geotechnical parameters couldn’t be accessible. So, the application of the certain analysis together with the probability analysis could be helpful. In this study, the direct shear test was conducted on silica sand samples contaminated with 2, 4, 6, 12 and 16% of gasoil and the stability probability analysis was evaluated by Monte Carlo method. The results showed that increasing the contaminant fraction led to reduction of internal friction angle and bearing capacity of the soil. This trend was observed with a slight reduction up to 6% and then with a sharper decline. In addition, two probability criteria of reliability and rapture probability (RP) were studied by Monte Carlo and then compared with factor of safety (FS).

This study investigates the capability of cement-SiO2 nanoparticles (CNS) mixture to the promotion of stabilization/solidification (S/S) process of heavy metal (HM) contaminated soils. For this purpose, artificially contaminated soil samples were first prepared by mixing kaolinite with nickel (Ni) and then a set of tests were performed to assess the effectiveness of the CNS treatment. The results indicate that the addition of cement markedly increases the HM retention of soil; however, the TCLP tests show that leaching of cement treated samples leads to return a part of pollutants to soil pore fluid. The cement and Ni interaction has a destructive impact on particles solidification which adversely affects the strength development and compressibility of the cement-stabilized specimens. At same condition, the CNS blend is more efficient in immobilizing Ni and modifying the soil engineering properties as compared to sole cement. Based on the physicochemical, XRD and SEM tests, the better performance of CNS agent is mainly associated with the more and faster growth of cement compounds, reducing the adverse effect of heavy metal precipitation on the hydration reactions and increasing the particle density. The study concluded that with the consideration of EPA criteria, an optimum cement content of 0.5 wt% per one cmol/kg.soil of HM within 28 days of curing can successfully remediate the Ni contaminated soils. The incorporation of SiO2 nanoparticles into the binder system improves the microstructure and geomechanical performance of stabilized materials and causes a significant reduction in the cement consumption (up to 35%) and time of curing (up to 3 times).

The purpose of the current paper is to extend a critical state constitutive model presented previously for sand behavior under monotonic loading such that it can predict behavior under cyclic loads as well. Due to the use of the critical state soil mechanics framework, the original model was able to predict sand behavior over a wide range void ratios and confining pressures, and take into account various aspects of behavior of loose and dense sands, including inherent and stress-induced anisotropies, softening and liquefaction of sands under monotonic loads. Extension of the base model for cyclic loading is accomplished through the use of bounding surface plasticity. Yield surface of the original model is used as the bounding surface of the new model, and also its loading surface using a deviatoric mapping rule. A new hardening modulus is used that enables predicting the behavior during loading and unloading. Flow rule of the original model is also modified in order to enable better prediction of the loading-unloading behavior, especially after phase transformation. Predictions based on this model showed satisfactory match with observed behavior of sands over a wide range of void ratios and confining pressures in drained and undrained monotonic and cyclic loading.