Modares Civil Engineering journal
Year:2016 | Volume:16 | Issue:3|Papers Count:20

Spur dike is one of the river training structures used for deviating the river flow from critical and erodible areas towards the central axis. As a result of flow, a zone with high turbulence around the spur dike is developed. The hydraulic process results development of the scour hole around the spur dike and settlement of sediment in the downstream and sides of the river. Several plan view shapes, such as straight, T-shape, and L-shape of spur dike have been constructed worldwide in accordance with different river environments. While scouring in spur dike structures results a serious threat to the river so it is needed to be investigated in this field. This paper describes flow field and scouring around series of Triplex rippling spur dikes (directed to the upstream) with a distance of 3.5 times of the effective length of the spur dike in the outer bank of a sharp bend channel. The first spur dike is located at section 30 degree from the start of bend. The experimental channel is a 90 degree channel with rectangular section. The radius of curvature to the channel width is 2, which is classified as a sharp bend. The bed materials used are uniform sand with mean diameter of 1.28 mm, its standard deviation coefficient of 1.3 and the relative density of sediment 2.35. Constant discharge of 25 l/s was used in the experiments. The results of flow field on flat bed and a scouring experiment are presented. The scouring test was done in 24 hours and in the moving threshold (U/Uc = 0.98) under clear water condition. Flow field was recorded using the Vectrino II profiling velocimeter (NORTEK) as it can profile water in a 3 cm column. Dye injection technique is also used for flow observation. It was found that in the levels upstream of the first spur dike and adjacent to the bed, stream lines are deviated towards the inner bank. While in the middle levels, flow lines upstream of the spur dike is almost parallel to the channel walls and approached the spur dike, resulting deviation in the separation zone. In the scouring experiment it was obvious that at the beginning of the experiment, thus creating the down flow upstream of the spur dikes, scouring initiates near the wing of each spur dike and further develops by the horseshoe vortex. Then after scour hole upstream of the second and third spur dike starts. Details of sediment movements at the beginning of the experiment and after development of the scour hole are addressed. The circulation flows and secondary flows which formed in bend and the position of separation zone at different layers are also discussed. Scouring experiment illustrate that the amount of scour at the upstream of the second spur dike is about 33 % and at the upstream of the third spur dike is about 81 % of the maximum amount of scour that occurs upstream of the first spur dike. The mechanism of scour and flow field are also studied in this paper.

The purpose of this research is to develop relationships to predict the results of measuring the electrical resistivity of the standard test method ASTM C1760 with assistance of other methods’ results. Comparative Methods in this paper are Impedance spectroscopy method, one electrode method and four electrode method. Impedance spectroscopy method is the most common in laboratory studies, ASTM C1760 method (Standard Test Method for Bulk Electrical Conductivity of Hardened Concrete) only has a standard rule and use in laboratory, one electrode method is a new technique in field and it’s application is in the reinforcement structures, and four electrode measurements are more common in field. In laboratory methods, bulk electrical resisitivity measured but in field, usually surface electrical resisitivty evaluated, that is why several source of errors affecting on the results of this test methods. To reach the aim of this research, 49 mix designs with a vast domination of electrical resistivity from about 40 (W-m) to 290 (W-m) was intended and for each of mix designs, 4 cylindrical and one reinforced slab specimen were made. reinforced slab specimen for one electrode measurement and cylindrical specimens for the other test method measurments were considered. Moreover, the electrical resistance of the aforementioned methods was measured at 28 days age. The results showed that there is a negligible difference between the results of impedance spectroscopy and ASTM C1760 methods; however, the electrical resistivity measured by ASTM C1760 method was slightly higher than the results of impedance spectroscopy method in the concrete. As a result, we can use the results of the impedance spectroscopy method instead of standard test method results in the lack of facilities with accepting about 5% of error. In the four electrode method, a number of factors including the imbalance among the distances between electrodes and structure dimensions can result systematic errors. That is why the measurements’ results with the method is approximately 140% larger than the standard test method results. Due to the lack of a comprehensive relationship for calculating the cell constant in the one electrode method, the value of this constant was obtained by comparing the results of the standard test method. After that, the electrical resistivity values were calculated. Electrical resistivity measurement results which was obtained by this method had also little difference with the standard test method results. Finally 3 relationships separately developed for predicting the result of standard test method from results of the each other test methods. Since the features and conditions of measuring by the standard test method are not available in the entire projects, the current results are capable to predict the standard method’s results with assistance of other methods’ results.

Bearing capacity failure and seismically-induced settlement of buildings resting on liquefied soils have resulted in significant damage in recent earthquakes. Majority of engineers still estimate seismic building settlement using procedures developed to calculate post-liquefaction reconsolidation settlement in the free-field. Previous studies of this problem have identified important factors involving shaking intensity, the liquefied soil’s relative density and thickness, and building's weight and width. Recent studies have also showed that shear deformation combined with localized volumetric strains during partially drained loading are dominant mechanisms. Bearing capacity degradation due to high excess pore water pressure development has also been reported in previous studies.In this study, two series of physical modelling experiments involving square and strip footings rested on saturated sand have been performed to identify the mechanisms involved in liquefaction-induced building settlements and bearing capacity degradation. The experiments have performed on Babolsar sand with moderate relative density in a box with transparent sides. Although earthquake waves can cause pore water pressure build up in saturated sands, complete liquefaction always do not occur. Anyhow, excess pore water pressure generation can cause damages to structures by bearing capacity degradation and excessive settlements. Various constant pore water pressure ratios were generated by static seepage through the base of the box to assess bearing capacity degradation and excessive settlements before and during complete liquefaction conditions. Constant pore water pressure ratio is representative of excess pore water pressure ratio generated during and sustained after earthquake excitation. First series of the experiments involved eight tests to evaluate bearing capacity of square and strip foundation in constant pore water pressure conditions. The results showed bearing capacity reduction due to excess pore water pressure development, but there was remarkable strength even during complete liquefaction that is related to post-liquefaction strength of liquefied sand. The square foundations are more affected than the strip ones at different constant excess pore water pressure ratios. Pore water pressure under the centerline of foundation decreased with loading increscent because of particle rearrangement and it was always smaller than the applied excess pore water pressure. Complete liquefaction has never observed under the footings. Safety factor selection is a challenging step in shallow foundation designs for most of engineers because of economical aspects. Recent studies show the important role of shear deformations in shallow foundations as discussed before. In the second test series of this experimental study, the foundations were loaded in three stages. first, initial loading was applied up to some safety factors and then settlements due to constant pore water pressure build up were measured in the second stage. Since then, loading was increased to complete bearing capacity failure in the third stage. This series include twelve tests for two types of foundations and various excess pore water pressures. Only shear deformations were assessed in these series because there was no volumetric deformation as excess pore water pressure was constant during the tests. The results demonstrate increase of foundation settlements with safety factor reduction progressively and settlements for safety factors larger than two were negligible.

Behavior of braced excavation in a cohesive-frictional soil has been evaluated by present paper. Two groups distinct analyses based on plastic calculations and consolidation calculations were implemented by considering time intervals of staged excavation. In order to investigation of time effect and pore water pressure impact on the staged excavation phases, numerical modeling has been conducted by help of consolidation and plastic analyses. In major of former analysis and before present study numerical analyses of staged excavation procedure have selected without considering the effect of time and in form of plastic analyses, while pore water pressures were also ignored. In this, paper thereto the time effect other effects such as length of time interval, kind of analysis depending on drainage conditions, constitutive modeling for soil and location of ground water table were considered. Two dimensional finite element analyses in PLAXIS 2D software are the basis of the numerical calculations of present study. Excavation bracing selected as a kind of concrete facing wall and grouted soil nailing. The results of this research show that the values of excavation wall lateral displacement and soil heave in bottom of the excavation in consolidation analysis by considering time effect in comparison with plastic analysis often reduced approximately 20%.It seems that effect of time and staged excavation just with implementation of numerical deflection analysis depending on the time such as consolidation analysis with creep models can be evaluated and these conditions in plastic numerical analysis with staged excavation without creep (time-depended) models is meaningless. Soft soil creep model (i.e. SSC model) for considering time effect in plastic and consolidation analyses has been used by authors. The results of present paper show that neither consideration of analyses that consider time interval nor analysis such as consolidation analysis that considers time are not adequate, but soil constitutive model that defines the material behavior must be contains time and also in their mathematic equations structure parameters such as time, strain rate and stress rate that vary with time must be taken into account. Present paper analyses show that consolidation analysis by considering time effect obtain less wall deflections by comparison with plastic analyses.However, from present study outcomes can conclude that the plastic analyses also by considering constitutive model that contain time can take into account time effects in stress-strain calculations. On the other hand, responses of plastic analyses by comparison with consolidation analyses always are preservative and show more values. Therefore, in structural designing of bracing of an excavation, reliance on results obtained from plastic analysis is preservative and real values of time-dependent deflections of wall and bottom of excavation via consolidation analyses are obtainable. This paper has recommended that both plastic and consolidation analyses for designing of braced cut were considered by engineers and optimum system between those according to the economically advantages and disadvantages be selected. Because, occasionally reliance on plastic preservative analyses lead to imposition of high values of design and construction costs on a certain project that is revealed by implementation of consolidation analyses that those are not necessary. At the end of the paper, verifications and comparisons are related to the topic of present study have been carried out by authors and the obtained results have been compared with together and then are investigated with the obtained results by present study.

Hybrid simulation which combines experimental and numerical modeling is a powerful and relatively new test method for evaluating the seismic performance of structural systems. In this method only critical components of structure are tested experimentally while the rest of the structure is numerically modeled in the computer. In this method the response of the structure is achieved by numerically integrating the equation of motion of the whole system. Among numerical integration methods, operator splitting (OS) method is of great interest for hybrid simulation, since not only its results are more accurate and stable in comparison with explicit methods but also its application for hybrid simulation is much more easier than implicit methods; the reason is that in OS method it is not required to conduct iteration on experimental element or estimate its tangent stiffness matrix during the simulation, the tasks which limit the application of implicit methods for hybrid simulation. But OS method suffers from the shortcoming that the use of initial stiffness matrix in its corrector step decreases the accuracy of results in nonlinear range. This paper presents a modified form of OS method which is termed MOS integration method in which by proposing a new procedure in the predictor step, the accuracy of this step is increased. When the accuracy of the predictor step increases, the difference between predictor and corrector displacements decreases and as a result the effect of initial stiffness approximation becomes less important. This would finally result in the improved accuracy of the whole simulation, as is shown in the paper.The performance, accuracy and stability characteristics of the proposed integration method were studied through numerical simulations, where it was assumed that the restoring force of the system is achieved experimentally and no information about the experimental stiffness is available. The results showed that for the wide range of considered systems including various natural periods, various ductility ratios and various degrees of freedom, MOS results are more accurate than OS method. This shows that the employed method of the predictor step of MOS method has successfully decreased the length of the corrector step with initial stiffness assumption. All the employed error indices also verified that not only the results of MOS are in great harmony with the reference solution but also its accuracy is improved over regular OS method, especially in simulations involving severe nonlinearity. Furthermore results of multi degree of freedom systems with high frequency modes show that MOS results are quite stable as long as the accuracy of important modes of the system is maintained, which is usually the case.As in a real hybrid simulation, experimental errors also affect the accuracy and stability of integration methods, in this paper a hybrid simulation algorithm is numerically modeled and the effect of actuator time delay on the performance of MOS method is investigated. It was observed that in the presence of actuator delay, which is known to be one of the most important sources of experimental errors in hybrid simulation, MOS integration method has solved the equation of motion in an accurate and stable manner with very small level of errors in comparison with the reference solution.

The two most common causes of embankment failure are embankment overtopping and internal erosion. Internal erosion of soil resulting from seepage flow is the main cause of serious hydraulic structures (dykes, dams) failure, in terms of the risk of flooding areas located downstream. The erosion characteristics are described by the Erosion Rate Index, which measures the increase in erosion rate with respect to an increase in the hydraulic shear stress; and the Initial Shear Stress, which represents the minimum hydraulic shear stress when erosion starts. The Erosion Rate Index ranges from 0 to 6, indicating that the changes in erosion rates in response to changes in hydraulic shear stress can differ by up to 106 times across different soils. Coarse-grained, noncohesive soils, in general, erode more rapidly and have lower Initial Shear Stresses than fine-grained soils. The challenge in predicting failure due to internal erosion is characterizing the material properties relevant to the rate of failure. Therefore, it is very important to improve the erosion resistance of soils using appropriate and cost effective techniques. In order to control internal erosion and treat erodible soil, the important point is to use modern stabilizers instead of traditional ones which are harmful. In this study, polyvinyl acetate polymer material has been used as a treatment for the erodibility of kaolinity clay sand. To conduct this research, kaolinity clay sand has been treated with different percentages of polyvinyl acetate polymer and it has been tested with hole erosion apparatus in different hydraulic gradients. The hole erosion test (HET) is one of several available procedures for characterizing the erodibility of cohesive soils that might be susceptible to internal erosion, in dams and levees. It was first developed in a constant-flow configuration (Lefebvre et al. 1984) and more recently in a constant-head configuration by Wan and Fell (2004). The HET utilizes an internal flow through a hole pre-drilled in the specimen, a flow condition similar to that occurring during piping erosion of embankment dams. In the constant-head configuration, the test head is typically doubled, starting from 50 mm, until progressive erosion of the pre-drilled hole is produced. Measurements of accelerating flow rate through an eroding pre-drilled hole in a test specimen yield estimates of the critical shear stress and erosion rate coefficient. The initial and final eroded hole diameters are used to compute initial and final friction factors, and intermediate hole diameters are then computed according to the flow rates measured during the course of the test. Result showed that the erosion rate of kaolinity clay sand is extremely rapid and polyvinyl acetate polymer stabilizer increased the resistance of kaolinity clay sand to erosion. It was also found out that with the addition of polyvinyl acetate polymer, the erosion type changes from extremely rapid to moderately slow. Adding polyvinyl acetate polymer caused the unconfined compression strength of kaolinity clay sand to increase by 60%.

Surface water contains various type of suspended impurities that cause turbidity and color. Coagulation is the main process of integrating fine particles and turn them into larger particles. In this study, replacement of the modeling methods by time-consuming and expensive experimental techniques such as JAR test has been discussed. For this purpose, two models of Feed forward and radial basis of artificial neural networks and Adaptive network-based fuzzy inference system and the various kinds of fuzzy regression analysis to predict the ultimate extent of turbidity after coagulation and flocculation process in 3 and 4 Tehran water treatment plants, were studied. The coagulant used in the treatment plant was poly-aluminum chloride (PAC) and the type and concentration of coagulant, pH and turbidity of the raw water, was opted from the basic information. Radial basis model due to the possibility of automatic raising of hidden layer’s neurons to achieve performance function with minimum error, is highly capable in simulating the process of coagulating. Unlike Feed forward networks, radial basis networks required a smaller number of neurons, and also had the ability to change parameters to achieve the desired results. Increasing the number of hidden layer’s neurons and normalizing the input data to the network enhanced the predictability of artificial neural networks. The study also generalize Feed forward networks to predict data validation and correction of the increasing of performance function. Due to the uncertainty which caused by human error in the laboratory, adaptive network-based fuzzy inference system and fuzzy regression, in which the data sets in the form of fuzzy, were used. The results showed that artificial neural networks and fuzzy regression analysis had more ability in simulating the coagulation process and turbidity removal in different experimental conditions rather than adaptive network-based fuzzy inference system and had the ability to replace the JAR test with time-consuming and expensive methods. The best network built to predict the filtered water turbidity in this study was feed forward network with two hidden layers and 6 and 8 neurons and Tansig and Purelin transfer functions respectively in the first and second layers, using normalized data with performance function. This network is able to predict the coagulation process with a Correlation Coefficient of 0.96 and 0.99 Agreement Index and root mean square error 0.0106. Best predicting done by regression analysis using fuzzy quadratic function. This function was able to predict the data validation with a correlation coefficient, and Agreement Index and root mean square error, respectively, 0.94, 0.96 and 0.75. adaptive network-based fuzzy inference system with the use of Gaussmf membership functions for raw water turbidity and pH input, and type and Trimf had best efficiency to apply coagulant concentration data into network and estimated the filtered water turbidity with correlation coefficient of 0.89, Agreement Index of 0.91, and squares error of 1.02. This system showed that increasing initial turbidity caused removal efficiency increased and the best impaction of coagulation process for the removal of turbidity would be occurred in the range of pH, 7.6 to 8. The best efficiency in operation condition was determined 99.5% in initial turbidity of 160 NTU, pH=8 and 19 mg/L dosage of PAC coagulant type I.

Understanding the combined effect of soil organic matter (SOM), surfactants and chelatant on the partitioning of polycyclic aromatic compounds and in soil/water systems and on their desorption is important to predict the effectiveness of surfactant-chelatant-enhanced remediation systems. In this paper the effect of soil organic matter’s content and presence of surfactants and a chelatant on desorption of six different polycyclic aromatic hydrocarbons namely acenaphthene, fluorine, phenanthrene, anthracene, fluoranthene, and pyrene was investigated and the results of phenanthrene was reported. It also investigates the effect of coexistence of three differenet heavy metals namely: lead, zinc and nickel on polycyclic aromatic hydrocarbons and their effects on desorption of these compounds. The basic soil was made from a mixture of kaolinite, montmorillonite and sand. Then this basic soil was spiked by two diffrenet level of organic matter through batch experiments to achieve three different soils named S0, S1 and S2 which has 0.33, 1.29 and 2.11 percent organic carbon, respectively. After that, this three different soils was spiked by heavy metals with the same way mentioned before (bathch experiments). As a result, six differenet soils was created under the name of: S0, S0M, S1, S1M, S2, S2M. and finally these six soils were spiked by mentioned polycyclic aromatic hydrocarbons. And finally the whole desorption experiments was done on these mentioned soils. Two surfactants chosen in this paper was triton x 100 and tween 80 and the chelatant was ethylene diamine tetraacitic acid (EDTA). Results showed that, surfactants improved the deorption of both heavy metals and polycyclic aromatic hydrocarbons and it also could be understood that triton x 100 had higher effectiveness than tween 80 in deorption of both heavy metals and polycyclic aromatic hydrocarbons. Furthermore it was found that soil organic matter had preventative effect on desorption of both heavy metals and polycyclic aromatic hydrocarbons. Both soil organic matter and surfactants are amphiphilic substances and because of that it is possible that this result is due to the sorption of surfactants into soil organic matter and consequently caused a reduction in desorption effectiveness of polycyclic aromatic hydrocarbons. and further increase in soil organic matter content caused more reverse effect on surfactants productivity. It was also found that, presence of lead, zinc and nickel could have preventative effect on desorption of polycyclic aromatic hydrocarbons too, and this could be due to some specific interactions like cation л binding between heavy metals and phenanthrene while they coexist in the interface of soil and water. Another reason of heavy metals preventative effect on desorption of polycyclic aromatic hydrocarbons could be due to their indirect effect through which, heavy metals act as an cation bridge between clay particles and organic matter mollecules and by this mean prevent soil organic matter mollecules to be dissolved in water. On the other hand scientists have proved that polycyclic aromatic hydrocarbons have great affinity to partition in to soil organic matter. Therefor by retaining more organic matter in soil through cation bridge mechanism, desorption of phenanthrene was reduced.

Saturated granular soils are possible liquefied when subjected to earthquake loading. This phenomenon is result from generation of excess water pore pressure because of non enough time to water drainage and govern non- Consolidated Condition.When liquefaction is occurred, many forces are generated and undergrounds structures are affected. In this research numerical analysis on buried pipelines in FLAC 2D software are performed and verified duration a comparative process with experimental result from ASCE organization. In present research surveyed effects of various parameters on liquefaction occurrence and probable damages to buried pipelines as dilatancy and friction angle of soil, relative density of back fill around the pipe, diameter and buried depth of pipe and underground water level.Results indicated that uplift of pipe decrease when dilatancy and friction angle of soil increased in constant relative density condition. This result is different for varied relative density. In low and medium relative density by increasing of dilatancy angle, uplift of pipe increase, reach to pick and decrease. But floating decrease with increasing dilatancy angle for high relative density always. Buried pipe in depth trench and increase of dead load result from back fill on pipeline and usage of pipes with small diameter, decrease uplift the pipe in liquefaction occurrence too. Of course don’t expect perform this subjects in all conditions. for example conflict ion to other underground installation, necessary hydraulic gradient for fluids flow or excavation in region with up underground level, don’t make to excavation of deep conduits. The analysis demonstrate that vertical displacement and damages to pipe is decrease if around installed pipe in conduit back fill with non- liquefied soils. In this new analysis all physical properties of soil and pipe in model are without any change except the cohesion and friction angle of soil around the pipe. Cohesion soils are low potential to liquefaction. For this reason we increase this coefficient from zero to 30 kpa and reach the friction angle to 30 degree. Results are demonstrated in a graph that show uplift versus thickness of non- liquefied soil normalized with diameter of pipe.Final parameter that surveyed in this research is effect of underground water level on floating buried pipeline. Results show decrease of underground water level cause to decrease of floating and damages to pipeline. For this purpose add a new water level to base model and run the analysis. In next steppes the underground water level is lesser and results are show in a graph that explain variation of vertical displacement versus water level normalized by thickness of soil model. This work possible by excavation of drainage shaft and drop down water level nearby the pipeline. Of course, look this work isn’t economical proposal for long transmission pipelines as petroleum or water conveyance. But in limit industrial sites as refineries this proposal is an improvement work to prevent any damage and and continual service of lifelines duration of unpredictable phenomenon.

Columns of the moment frames are subjected to high axial forces as well as inelastic rotations during a seismic event. Estimating the boundaries for these simultaneous structural demands on the columns of special moment frames are one the aims of this research. These demands are evaluated by performing a vast number of non-linear time history analyses on some archetype frames. Totally, eight archetype buildings are designed under two levels of spectral accelerations representing the Maximum Credible Earthquake (MCE) and the Design Earthquake (DE). Both geometric and material nonlinearities are taken into account. Far-field earthquake record set -proposed by FEMA P696- is utilized in this study to conduct the required time history analyses. This set includes 44 individual seismic records with different magnitudes and other specifications. Each sample special moment frame is excited by each of the individual records with two different intensity levels referring to DE and MCE respectively. After performing numerous time history analyses, the boundaries and the values for the axial force and the story drift ratio on columns are fairly stablished for the seismic events with MCE and DE intensity levels. It is proved that the columns might experience the axial force around 30% of their yielding capacity as well as the drift ratios up to 6%. Effects of simultaneous changes in axial force and plastic rotation in such columns are neglected in available loading frameworks (protocols, setups, what?!) for these members. On the other hand, existing loading frameworks are introduced quite arbitrarily in different research studies, with no root in the real seismic demands of these structural members. Hence, a statistical approach implemented to extract the loading cycles based on the results of the mentioned non-linear time histories. Therefore, a representative loading protocol is also developed for the column members of special moment frames with the aid of the results of the supportive analyses. This loading protocol includes cycles of varied axial force ratios as well as simultaneous cycles of lateral loading.Providing such a loading regime can pave the way to investigate the behavior of the columns of moment frames by more sophisticated numerical models which cannot be ordinarily employed to perform costly time history analyses under seismic records. The overall response of steel columns may be dominantly affected by the local effects like as local bucking at large deflections. Hence, the response of some archetype individual columns is fairly investigated under the proposed loading protocol by utilizing continuum finite element simulations which are expected to capture these kinds of local effects deliberately. The investigation not only reveales more on the details of the behavior of these members, but also proves the versatility of the proposed loading protocol in comparison with the previous loading procedures. In order to do so, the numerical models of the archetype columns are also examined under the proposed lateral loading protocol. Accordingly, constant levels of axial loading and the results of both cases are compared. It is shown that implementing a constant axial load besides the cyclic lateral cyclic loading may not be an appropriate loading framework and the results would not represent the seismic demands in these members accurately.

Premature failures are sometimes experienced in road pavements. Among the various failure modes, moisture damage is probably the most occurring distress in asphalt pavements. In fact, the continuous presence of water in asphalt layers weakens the bond between aggregate particles and bitumen, ending in stripping of mixes. Several parameters affect the damages of water to asphalt layers. Among these, aggregates type and source, bitumen type and grade, mixture design, construction practice, traffic volume, environment and the additive properties can be named as the most effective parameters.In order to prevent stripping, one of the most effective methods is to use anti-stripping additives. Among the various additives, sulphur, which is a byproduct of petroleum gas production industries, has been known to increase stiffness of bituminous mixes appreciably, provided that it is added properly and at right amounts. However, due to environmental drawbacks of this additive (i.e. emission of disturbing gases) and the too-much-stiffening effects that it imparts to mixes, sulphur alone was banned to be used in road pavements for several decades. In the recent years, combined additives, consisting of sulphur and polymers have been produced and applied into asphalt mixes. It has been proved that these additives have less adverse environmental effects (i.e. reduced emission of gases such as h2s). The effects of these additive types is so that their sulphur component provides stiffness to mixes and their polymer portion imparts some flexibility to mixes and increase the adhesion properties of the mix binders.“ASTM D8” Standard Testing Method.In this research a locally produced sulphur polymer additive, named ‘Googas’, was used and applied in a continuously graded asphalt mix. This new product had lower emissions of h2s gas, compared with the conventional sulphur mixes. In addition, it provided enhanced properties to mixes, compared with previously made only-sulphur-containing mixes. In order to reduce the stiffness of mixes and provide these with more flexibility, CRM (Crumb Rubber Modifier) modified binders were replaces with the conventional penetration grade binder of mixes. CRM binders were prepared containing different amounts of crumb rubber. The preparation was carried out in laboratory using a high shear rate mixer.The results showed that increased amounts of Googas sulphur polymer although resulted in increased compression strength, reduced the moisture resistance of mixes substantially. In fact, it was seen that when asphalt mixes were cooled to ambient temperatures, sulphur tended to change from liquid into solid state, contributing little to bitumen cohesiveness. In contrast, mixes containing CRM binders alone, showed increased tensile properties, as indicated by increased ITS testing results. By analyzing the laboratory results, optimum amounts of the above two additives were determined. In fact, increased amounts of CRM resulted in increased tensile resistance of mixes (i.e. showing a gradual increasing trend). This happened for CRM of up to 18 to 20%. Further increases resulted in lower tensile strengths. Hence, optimized mixes were designed containing both CRM and sulphur polymer additives.

In this paper, a new scheme is presented for controlling the structural vibrations, excited by the external dynamic effects such as the earthquake and etc. The proposed method is an active control technique which is compatible with the structural dynamic behavior. In the other words, the proposed active control method is formulated based on the structural dynamics theories. This approach could be used for designing a control mechanism with multi actuators and multi sensors. For this purpose, the actuator’s forces vector is added to the dynamic equilibrium equations of the motion. The vector of the actuator’s forces is independent of the natural dynamic equilibrium equations of system and the elements of this vector are determined based on the active control strategy. This paper presents an innovate concept to formulate the external control forces which are applied to the main structure by the actuators. For calculating the control forces, each actuator force is modeled as an equivalent viscous damper. If there is m actuator attached to the structure, m actuator force should be determined in the control process. Based on the proposed technique, each actuator force is considered as a viscous force, added to the dynamic equations of motion. Therefore, there is m unknown force in the control system. These m unknown parameters should be calculated at each instant time of the control process which leads to reduce the structural vibration. For determining these m unknown actuator forces, m additional equations is required. Here, the critical damping concept of the structural dynamics theory is utilized to prepare the required equations. For this purpose, the actuator forces are determined so that several lower vibration modes are damped critically. In the other words, m actuator force is calculated if the m initial vibration’s modes are in the critical conditions. By creating critical damping condition for m initial vibration’s mode, a set of m simultaneous equations is achieved. In each time instance of the control process, the m actuator forces are determined by solving this set of simultaneous equations. As a result, the proposed control mechanism is formulated by a simple mathematical formulation. On the other hand, the proposed method does not depend on the type of the dynamic load and it could be applied to control each structure with multi degrees of freedom. It should be noted that running these process in the case of multi actuator is the main originality of this paper. In the other words, a similar control procedure is performed for a system with single actuator. For numerical verification of the proposed method, some criterions such as the maximum displacement are evaluated in a five-story shear building which is excited by the seismic load i.e. the Elcentro Earthquake. This study shows that the proposed active control method has sufficient accuracy and suitable efficiency for decreasing the structural vibrations. According to the numerical results, the maximum drift in the upper floor of this five-story shear building is reduced by 55%. By increasing the number of actuators, the control process with higher efficiency is achieved.

Using reinforced elements to improve geotechnical properties of soil, has been considered by researchers for many years. In recent years, significant progress has been made in the field of improving poor soils and reinforcing them. Soil reinforcement is used as an effective method to improve the soil layers in order to increase the bearing capacity and reduce settlement. Soil-bag system is one of the new polymer products that can be used as a soil reinforcing element in various projects. Soil-bag system was developed in order to increase the bearing capacity of the soil and reduce its settlement. In this study, bed soil models in reinforced and non-reinforced conditions have been investigated using a numerical method. Numerical studies have been carried out in 3 dimensional cases using finite element method. In this method, sand and polymer bag behavior were defined by using Mohr–Coulomb and Elastic-Perfect Plastic models. Also, the effects of soil-bag system in increasing the bearing capacity and reducing settlement were evaluated. The results properly correspond to the ones obtained from numerical studies and field studies carried out by other researchers. The results show that the bearing capacity of the reinforced bed is almost 2 times bigger than that of the non-reinforced bed.One of the resistance-based parameters of soil-bag system is the thickness of polymeric bag. When the thickness of polymeric bag is considered to be 0.5mm, the maximum displacement will reach to 13.1 mm. While if the thickness of polymeric bag becomes double, i.e. if it is considered as 1 mm, the maximum displacement will reach to 11.6 mm. Another resistance-based parameter of soil-bag system, which was examined in this research, is the effect of internal friction angle of soil on the bearing capacity of soil-bag system. The results show that the more the friction angle between soil particles is, the more the resistance of soil-bag system against the external loading will be.The type of filling material mostly depends on the application of soil-bag system and the availability of material. The most important characteristic of soil-bag system is the tension strength of the polymer in the bags. The bags are generally made of polyethylene or polypropylene polymers. Earth reinforcement using soil-bag system causes to increase soil bearing capacity and to minimize the transformation of foundation bed due to the imposed load. The results of simple pressure test on the foundation reinforced by soil-bag system show that when soil-bag system is subject to external load, it exhibits high strength a great portion of which is resulted from the tension force generated in the cover of the polymeric bag.

Open-channel junctions have a broad application in civil and environmental engineering. Formation of a low-pressure zone with recirculating flow (high sedimentation potential) accompanied by a high-velocity zone (high erosion potential) are the most characteristic features of flow in junctions. A large number of researches have been performed to grasp the complicated concept of hydraulic phenomena and correct the related deficiencies in the straight junction of open-channel flows. The interaction between the main and branch flows, causes the main flow to be diverted toward the opposite bank of junction and this interaction creates a separation zone at the downstream corner of the junction. Formation of a three dimensional (3D) separation zone with lower pressure immediately near the branch-side bank is one of the most distinctive characteristics of a flow in open-channel junctions. In addition to, the recirculating flow in this low-pressure zone not only prepares a suitable space for sedimentation which is a common problem in hydraulic structures that can block intakes or junctions, but also increases the velocity near the opposite bank of the main channel and its bed and thereby leads to local erosion. Thus, reducing the sedimentation potential in recirculation zone and eliminating the erosion near the opposite wall of the channel are two major concerns for designers of open-channel junctions. For this purpose, different researches from using submerged vanes in main channel to the geometrical modifications of the junction entrance, have been conducted to improve the flow pattern around the junctions. Therefore, implementing a separating wall in the middle of the branch channel is thoroughly investigated in this research to understand its effect on the flow pattern and also its contribution in reducing the sedimentation and erosion potential in an open-channel junction. Initially, the numerical two-phase model of a previous experimental study, is prepared and its results are validated. Following that, a one-phase model is prepared based on the fact that the difference between maximum and mean elevation of water free surface is less than 10%. According to the negligible (less than 3%) discrepancy between numerical one-phase and two-phase results in predicting the maximum U* after the junction in channel, acceptable similarity between U* contours and U* variation along the flow depth in numerical (one-phase) and experimental studies and considerable increase in computation time of two-phase analysis, one-phase analysis is implemented instead of two-phase one in the rest of this research.Finally, effects of separating wall are evaluated in a large-scaled industrial 90o open-channel junction and some new geometrical efficiency measurements are devised and assessed to improve the wall performance. Among proposed geometrical modifications on the wall head, semicircular profile had the best performance in reducing the maximum velocity after the junction. The results show a considerable improvement in flow pattern which causes a significant reduction in sedimentation and erosion potential in open-channel junctions.

Development of erosion and sedimentation processes due to human activities or natural changes will threaten the stability of the rivers and cause hydraulic and morphological changes. Continuous changes will result in a lot of damages including damage to structures constructed in the rivers. Therefore, preserving the rivers in the equilibrium (regime) state is of great importance. In other words, determination of the stable hydraulic geometry of the rivers is one of the most important factors on which the design, planning, management and training of a river are founded. Two basic approaches have been used to predict the hydraulic geometry of gravel-bed rivers: (1) Those based on empirical regime equations; and (2) those based on the simultaneous solution of the governing equations of channel flow. Currently, there are considerable restrictions with the use of both methods for channel design. The existing experimental hydraulic geometry relationships have been obtained for particular field conditions and based on limited data, and can be used only under the same conditions. Equally, theoretical methods are applicable only to straight or fixed width and with static stability channels. Due to the lack of knowledge regarding the mechanisms controlling width adjustment and meander development, the basic assumptions of a large number of theories, developed in this regard, include a steady and uniform flow as well as stream changes toward the equilibrium state. The main difference between these theories is the hydraulic mechanisms employed by the models to describe how the stream reaches to equilibrium state. In this Paper, an analytical model for assessing the stable condition (static and dynamic stability) and predicting river response to the changes applied (such as hydraulic changes) was proposed. In addition, univariate and bivariate hydraulic geometry relationships were derived to be applied in the rivers with dominant bed load. For this purpose, after reviewing the previous researches in this field, the principles and concepts of the regime and hydraulic geometry were presented. In the next step, a system of equations was solved excluding bank stability constraint (unconstrained model), using the analytical model. Due to the lack of required equations to solve the system, extremal hypotheses were used. According to these theories, the river behavior is justified in order to optimize a specific morphologic parameter. A proper agreement was observed between the developed exponents of hydraulic geometry relationships in this paper and the results of the empirical and analytical hydraulic geometry relationships. This represents the self-adjusting mechanism of alluvial channels by introducing the channel shape factor (bed width/depth ratio) and the inclusion of extremal hypotheses in the flow governing equations (continuity, flow resistance and sediment transport equations). Finally, the developed model was calibrated using the field data of the United Kingdom. The mean relative error of the bankful width and depth calculation is obtained 47% and 35%, respectively. The obtained results confirmed the efficiency of the proposed model.

Reliability analysis of steel structures subject to seawater corrosion is of considerable interest for coastal and offshore marine steel structures. These are often very expensive and have high consequential costs and implications should failure occur. Since corrosion of steel structures causes deterioration of structural strength, usually gradually with time, safety assessment is of considerable importance for new structures (those in the design stage) and also for those which are already in operation.Marine corrosion is a complex phenomenon and subject to various influencing factors each of which has its own inherent uncertainty. In any safety assessment, in principle, the uncertainty of each factor should be studied and taken into account. Since such an action is too difficult, in practice some test programs are normally conducted and all uncertainties caused by different factors are assumed to be included in the relevant corrosion measurements.In addition, in any corrosion reliability analysis for steel structures exposed to seawater, two different models must be taken into consideration: (1) A physical model indicating general corrosion behaviour as a function of exposure time and (2) A stochastic model describing probabilistic treatment of uncertainties observed in real corrosion data. The first has been traditionally treated by invoking a simple power law and in particular a linear relationship. However, using realistic long-term data, validity of such a model has recently been challenged. The second model (i.e. probabilistic modelling of corrosion process) has been dealt with in literature in different approaches, including either taking the corrosion annual rate as a random variable or proposing a stochastic process such as Gamma process. This is usually proposed as a general structural deterioration process. The second approach provides, doubtlessly, better treatment of corrosion uncertainties; however it can be shown unfortunately that the Gamma process is unable to reflect the corrosion uncertainties in some circumstances.In this paper, two sets of corrosion data collected in different seawaters around the world with different temperatures are used. This requires processing of data in such a way that the data sets remain consistent with each other and that outcome is data that can be considered as belonging to one statistical population. Herein, first, a simple algorithm is proposed to transform the whole data to one common temperature. Second, a novel Markov-chain based model is developed which meets long term second-order corrosion statistics (i.e. means and standard deviations of corrosion losses). It is based on a corrosion model that previously has been calibrated extensively to field observations of corrosion and to literature-reported realistic data. Although actual long-term field observations of marine corrosion of steel are scarce, it is shown that particularly for the standard deviation the new model is well capable to be consistent with the long-term data.It is noted that herein, only the corrosion data collected in marine immersion zones are considered (i.e. those taken in splash zones and atmospheric zones are not considered). Further, only general corrosion (i.e. not pitting corrosion) is accounted for herein. These two issues, obviously, have to be addressed separately.

The use of lateral intake is one method of providing water from river. The most important issue in branch channel gets the maximum of water and lowest sediment. The rivers rarely run on straight paths in nature, and most rivers have meandering forms. In a river bend the presence of centrifugal force leads to the formation of secondary flow. As a result water particles near the surface are driven outward. The secondary flow advects the main flow, leading to high velocity at the outer bank of the bend. On the other hand the flow at the bed of a channel is directed toward the inner bank. The interaction of the main flow with the secondary flow forms the so-called helical flow in the bend. This flow system has important consequences in the longitudinal, transverse, vertical velocity distributions, transport of momentum and streamlines at different levels of water. Therefore layout the intake outer bank of bend is one of the ways to reduce sediment input to the lateral intake. Combining the helical flow and complex flow pattern in front of the lateral intake is added complexity of this three- dimensional flow pattern. The flow approaches the intake; it is accelerated laterally by the suction pressure at the end of the branch channel. This causes the flow to divide so that a portion enters the branch channel with the remainder continuing downstream in the main channel. The portion withdrawn by the branch is delineated by a curved shear-layer surface, denoted as the dividing stream surface Because of the stream wise curvature of the dividing stream surface, the diverted flow experiences an imbalance between the transverse pressure gradient and shear and centrifugal forces that initiates a clockwise secondary motion cell. This secondary motion interacts with the separation zone along the inner wall of the branch channel. In design of lateral intakes, determination of appropriate intake location and diversion angle is very important. In this paper, we simulated lateral intake at different location and different angel by using the SSIIM numerical model to investigate dividing stream surface and separation zone at main and branch channel. For this purpose the flow is simulated using standard k-e model and RNG model. For calibration of model we used the result of the Montaseri et.al (2008) investigation. The results show that in the curved channel the dividing stream surface has a completely different structure than the lateral diversion in a straight one. In other words, wide of dividing stream surface near bed is smaller than near surface. Furthermore, in any locations dividing stream surface width near the bed and separation zone has largest dimension at 90 degree diversion angle and has smallest dimension at 30 degree diversion angle. Also, in 135 degree location, dividing stream surface width near the bed has smallest dimension and dividing stream surface width near the surface has largest dimension at any diversion angle.

Failure of a concrete gravity dam will cause inevitable human loss and financial damages. In this study SARIYAR concrete gravity dam, located in turkey was chosen as a case study, to investigate the probability of the dam’s sliding failure in various conditions. The most important reason of sliding failure in a concrete dam is lateral and uplift loads, caused by increase in the level of reservoir water. Different scenarios were considered which might happen to a dam, simulating all the possible water levels of reservoir. Afterwards, the probability of failure and reliability index were calculated with Monte Carlo simulation and FORM method, in all conditions and comparison was carried out between the results. The influence of the Number of Simulations (NOS) in the Monte Carlo method was also discussed. Results showed that, in some cases, the system resistance was much more than the loads, and the limit state function had a significant distance from the samples. In such states, Monte Carlo was unable to calculate the probability of failure with each NOS. However, FORM method could obtain the Reliability Index (b) in these situations. It was found out that these values were far from the reality. With increase in the forces, the degree of precision of the responses from Monte Carlo grew high. The probability of failure generated by FORM method was less than that in reality. The failure of a concrete gravity dam will cause inevitable human loss and financial damages. In this study SARIYAR concrete gravity dam, located in turkey was chosen as a case study, to investigate the probability of the dam’s sliding failure in various conditions. The most important reason in sliding failure of a concrete dam is lateral and uplift loads, caused by increase in the reservoir water level. Different scenarios were considered which might happen to a dam, simulating all the possible reservoir water levels. Thereafter, the probability of failure and reliability index was calculated with Monte Carlo simulation and FORM method, in all conditions and the results were compared to each other. The effect of the Number of Simulations (NOS) in the Monte Carlo method was also discussed. Results showed that, in some cases, the resistance of the system was much more than the loads, and the limit state function had a significant distance from the samples. In such states, Monte Carlo was unable to calculate the probability of failure with each NOS, while FORM method managed to obtain the Reliability Index (b). It became clear that these values were far from the reality.

Structural safety in the design of civil engineering projects has always been significantly important for engineers. One of the failure mechanisms of structures which is recently attended is progressive collapse. Progressive collapse of structures during earthquakes and even explosions near the construction has become a major challenge, creating problems for structures, and may even lead to the destruction of the entire structure. Progressive collapse is defined as extension of primary local failure from an element to another element that finally collapses the entire structure or a major part of it. Potential hazards that cause progressive collapse are fires, gas explosions, accidents, bombs etc. the purpose of this paper is to investigate progressive collapse in steel structures with centrically braced frames, and the influence of parameters such as height, bracing arrangement and type of structural system. In this study, the progressive collapse due to column removal in steel centrically braced frames that are designed seismically according to Iranian guidelines is analyzed using alternate path method and nonlinear dynamic analysis. Also, the progressive collapse due to column and brace removal is simultaneously analyzed in steel centrically braced frames. The analysis of the progressive collapse in moment frame and the comparison of it with centrically braced frames will also be carried out. For this purpose, two five- and ten-story structures with braces in the middle spans, and also two five- and ten-story structures with braces in lateral spans were analyzed using ETABS program. One of the five-story structures was with system of moment frames and the other one with a combinational system of moment frames centrically braced. Thereafter, the progressive collapse was modeled in SAP2000 program for one of the structures with outside frames. Results showed that the removal of a single column only when there is no brace beside the removed column, and also simultaneous removal of columns and braces only in the last floor cause progressive collapse of the structure. Also, the probability of progressive collapse with simultaneous removal of columns and braces will increase when the height of the frames centrically braced increases, and will decrease when the height of the frames laterally braced increases. Also the comparison of centrically braced frames with moment frames showed that centrically braced frames are more resistant to the progressive collapse than the moment frames. However, combinational system of moment frames and centrically braced ones in comparison with the other analyzed systems is the most resistant system to progressive collapse.